Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

12 files changed, 4907 insertions, 0 deletions

diff --git a/Documentation/s390/3270.ChangeLog b/Documentation/s390/3270.ChangeLog
new file mode 100644
index 000000000000..031c36081946
--- /dev/null
+++ b/Documentation/s390/3270.ChangeLog
@@ -0,0 +1,44 @@
+ChangeLog for the UTS Global 3270-support patch
+
+Sep 2002:	Get bootup colors right on 3270 console
+	* In tubttybld.c, substantially revise ESC processing so that
+	  ESC sequences (especially coloring ones) and the strings
+	  they affect work as right as 3270 can get them.  Also, set
+	  screen height to omit the two rows used for input area, in
+	  tty3270_open() in tubtty.c.
+
+Sep 2002:	Dynamically get 3270 input buffer
+	* Oversize 3270 screen widths may exceed GEOM_MAXINPLEN columns,
+	  so get input-area buffer dynamically when sizing the device in
+	  tubmakemin() in tuball.c (if it's the console) or tty3270_open()
+	  in tubtty.c (if needed).  Change tubp->tty_input to be a
+	  pointer rather than an array, in tubio.h.
+
+Sep 2002:	Fix tubfs kmalloc()s
+	* Do read and write lengths correctly in fs3270_read()
+	  and fs3270_write(), whilst never asking kmalloc()
+	  for more than 0x800 bytes.  Affects tubfs.c and tubio.h.
+
+Sep 2002:	Recognize 3270 control unit type 3174
+	* Recognize control-unit type 0x3174 as well as 0x327?.
+	  The IBM 2047 device emulates a 3174 control unit.
+	  Modularize control-unit recognition in tuball.c by
+	  adding and invoking new tub3270_is_ours().
+
+Apr 2002:	Fix 3270 console reboot loop
+	* (Belated log entry) Fixed reboot loop if 3270 console,
+	  in tubtty.c:ttu3270_bh().
+
+Feb 6, 2001:
+	* This changelog is new
+	* tub3270 now supports 3270 console:
+		Specify y for CONFIG_3270 and y for CONFIG_3270_CONSOLE.
+		Support for 3215 will not appear if 3270 console support
+		is chosen.
+		NOTE:  The default is 3270 console support, NOT 3215.
+	* the components are remodularized: added source modules are
+	  tubttybld.c and tubttyscl.c, for screen-building code and
+	  scroll-timeout code.
+	* tub3270 source for this (2.4.0) version is #ifdeffed to
+	  build with both 2.4.0 and 2.2.16.2.
+	* color support and minimal other ESC-sequence support is added.
diff --git a/Documentation/s390/3270.txt b/Documentation/s390/3270.txt
new file mode 100644
index 000000000000..0a044e647d2d
--- /dev/null
+++ b/Documentation/s390/3270.txt
@@ -0,0 +1,274 @@
+IBM 3270 Display System support
+
+This file describes the driver that supports local channel attachment
+of IBM 3270 devices.  It consists of three sections:
+	* Introduction
+	* Installation
+	* Operation
+
+
+INTRODUCTION.
+
+This paper describes installing and operating 3270 devices under
+Linux/390.  A 3270 device is a block-mode rows-and-columns terminal of
+which I'm sure hundreds of millions were sold by IBM and clonemakers
+twenty and thirty years ago.
+
+You may have 3270s in-house and not know it.  If you're using the
+VM-ESA operating system, define a 3270 to your virtual machine by using
+the command "DEF GRAF <hex-address>"  This paper presumes you will be
+defining four 3270s with the CP/CMS commands
+
+	DEF GRAF 620
+	DEF GRAF 621
+	DEF GRAF 622
+	DEF GRAF 623
+
+Your network connection from VM-ESA allows you to use x3270, tn3270, or
+another 3270 emulator, started from an xterm window on your PC or
+workstation.  With the DEF GRAF command, an application such as xterm,
+and this Linux-390 3270 driver, you have another way of talking to your
+Linux box.
+
+This paper covers installation of the driver and operation of a
+dialed-in x3270.
+
+
+INSTALLATION.
+
+You install the driver by installing a patch, doing a kernel build, and
+running the configuration script (config3270.sh, in this directory).
+
+WARNING:  If you are using 3270 console support, you must rerun the
+configuration script every time you change the console's address (perhaps
+by using the condev= parameter in silo's /boot/parmfile).  More precisely,
+you should rerun the configuration script every time your set of 3270s,
+including the console 3270, changes subchannel identifier relative to
+one another.  ReIPL as soon as possible after running the configuration
+script and the resulting /tmp/mkdev3270.
+
+If you have chosen to make tub3270 a module, you add a line to
+/etc/modprobe.conf.  If you are working on a VM virtual machine, you
+can use DEF GRAF to define virtual 3270 devices.
+
+You may generate both 3270 and 3215 console support, or one or the
+other, or neither.  If you generate both, the console type under VM is
+not changed.  Use #CP Q TERM to see what the current console type is.
+Use #CP TERM CONMODE 3270 to change it to 3270.  If you generate only
+3270 console support, then the driver automatically converts your console
+at boot time to a 3270 if it is a 3215.
+
+In brief, these are the steps:
+	1. Install the tub3270 patch
+	2. (If a module) add a line to /etc/modprobe.conf
+	3. (If VM) define devices with DEF GRAF
+	4. Reboot
+	5. Configure
+
+To test that everything works, assuming VM and x3270,
+	1. Bring up an x3270 window.
+	2. Use the DIAL command in that window.
+	3. You should immediately see a Linux login screen.
+
+Here are the installation steps in detail:
+
+	1.  The 3270 driver is a part of the official Linux kernel
+	source.  Build a tree with the kernel source and any necessary
+	patches.  Then do
+		make oldconfig
+		(If you wish to disable 3215 console support, edit
+		.config; change CONFIG_TN3215's value to "n";
+		and rerun "make oldconfig".)
+		make image
+		make modules
+		make modules_install
+
+	2. (Perform this step only if you have configured tub3270 as a
+	module.)  Add a line to /etc/modprobe.conf to automatically
+	load the driver when it's needed.  With this line added,
+	you will see login prompts appear on your 3270s as soon as
+	boot is complete (or with emulated 3270s, as soon as you dial
+	into your vm guest using the command "DIAL <vmguestname>").
+	Since the line-mode major number is 227, the line to add to
+	/etc/modprobe.conf should be:
+		alias char-major-227 tub3270
+
+	3. Define graphic devices to your vm guest machine, if you
+	haven't already.  Define them before you reboot (reipl):
+		DEFINE GRAF 620
+		DEFINE GRAF 621
+		DEFINE GRAF 622
+		DEFINE GRAF 623
+
+	4. Reboot.  The reboot process scans hardware devices, including
+	3270s, and this enables the tub3270 driver once loaded to respond
+	correctly to the configuration requests of the next step.  If
+	you have chosen 3270 console support, your console now behaves
+	as a 3270, not a 3215.
+
+	5. Run the 3270 configuration script config3270.  It is
+	distributed in this same directory, Documentation/s390, as
+	config3270.sh.	Inspect the output script it produces,
+	/tmp/mkdev3270, and then run that script.  This will create the
+	necessary character special device files and make the necessary
+	changes to /etc/inittab.  If you have selected DEVFS, the driver
+	itself creates the device files, and /tmp/mkdev3270 only changes
+	/etc/inittab.
+
+	Then notify /sbin/init that /etc/inittab has changed, by issuing
+	the telinit command with the q operand:
+		cd Documentation/s390
+		sh config3270.sh
+		sh /tmp/mkdev3270
+		telinit q
+
+	This should be sufficient for your first time.	If your 3270
+	configuration has changed and you're reusing config3270, you
+	should follow these steps:
+		Change 3270 configuration
+		Reboot
+		Run config3270 and /tmp/mkdev3270
+		Reboot
+
+Here are the testing steps in detail:
+
+	1. Bring up an x3270 window, or use an actual hardware 3278 or
+	3279, or use the 3270 emulator of your choice.  You would be
+	running the emulator on your PC or workstation.  You would use
+	the command, for example,
+		x3270 vm-esa-domain-name &
+	if you wanted a 3278 Model 4 with 43 rows of 80 columns, the
+	default model number.  The driver does not take advantage of
+	extended attributes.
+
+	The screen you should now see contains a VM logo with input
+	lines near the bottom.  Use TAB to move to the bottom line,
+	probably labeled "COMMAND  ===>".
+
+	2. Use the DIAL command instead of the LOGIN command to connect
+	to one of the virtual 3270s you defined with the DEF GRAF
+	commands:
+		dial my-vm-guest-name
+
+	3. You should immediately see a login prompt from your
+	Linux-390 operating system.  If that does not happen, you would
+	see instead the line "DIALED TO my-vm-guest-name   0620".
+
+	To troubleshoot:  do these things.
+
+	A. Is the driver loaded?  Use the lsmod command (no operands)
+	to find out.  Probably it isn't.  Try loading it manually, with
+	the command "insmod tub3270".  Does that command give error
+	messages?  Ha!  There's your problem.
+
+	B. Is the /etc/inittab file modified as in installation step 3
+	above?  Use the grep command to find out; for instance, issue
+	"grep 3270 /etc/inittab".  Nothing found?  There's your
+	problem!
+
+	C. Are the device special files created, as in installation
+	step 2 above?  Use the ls -l command to find out; for instance,
+	issue "ls -l /dev/3270/tty620".  The output should start with the
+	letter "c" meaning character device and should contain "227, 1"
+	just to the left of the device name.  No such file?  no "c"?
+	Wrong major number?  Wrong minor number?  There's your
+	problem!
+
+	D. Do you get the message
+		 "HCPDIA047E my-vm-guest-name 0620 does not exist"?
+	If so, you must issue the command "DEF GRAF 620" from your VM
+	3215 console and then reboot the system.
+
+
+
+OPERATION.
+
+The driver defines three areas on the 3270 screen:  the log area, the
+input area, and the status area.
+
+The log area takes up all but the bottom two lines of the screen.  The
+driver writes terminal output to it, starting at the top line and going
+down.  When it fills, the status area changes from "Linux Running" to
+"Linux More...".  After a scrolling timeout of (default) 5 sec, the
+screen clears and more output is written, from the top down.
+
+The input area extends from the beginning of the second-to-last screen
+line to the start of the status area.  You type commands in this area
+and hit ENTER to execute them.
+
+The status area initializes to "Linux Running" to give you a warm
+fuzzy feeling.  When the log area fills up and output awaits, it
+changes to "Linux More...".  At this time you can do several things or
+nothing.  If you do nothing, the screen will clear in (default) 5 sec
+and more output will appear.  You may hit ENTER with nothing typed in
+the input area to toggle between "Linux More..." and "Linux Holding",
+which indicates no scrolling will occur.  (If you hit ENTER with "Linux
+Running" and nothing typed, the application receives a newline.)
+
+You may change the scrolling timeout value.  For example, the following
+command line:
+	echo scrolltime=60 > /proc/tty/driver/tty3270
+changes the scrolling timeout value to 60 sec.  Set scrolltime to 0 if
+you wish to prevent scrolling entirely.
+
+Other things you may do when the log area fills up are:  hit PA2 to
+clear the log area and write more output to it, or hit CLEAR to clear
+the log area and the input area and write more output to the log area.
+
+Some of the Program Function (PF) and Program Attention (PA) keys are
+preassigned special functions.  The ones that are not yield an alarm
+when pressed.
+
+PA1 causes a SIGINT to the currently running application.  You may do
+the same thing from the input area, by typing "^C" and hitting ENTER.
+
+PA2 causes the log area to be cleared.  If output awaits, it is then
+written to the log area.
+
+PF3 causes an EOF to be received as input by the application.  You may
+cause an EOF also by typing "^D" and hitting ENTER.
+
+No PF key is preassigned to cause a job suspension, but you may cause a
+job suspension by typing "^Z" and hitting ENTER.  You may wish to
+assign this function to a PF key.  To make PF7 cause job suspension,
+execute the command:
+	echo pf7=^z > /proc/tty/driver/tty3270
+
+If the input you type does not end with the two characters "^n", the
+driver appends a newline character and sends it to the tty driver;
+otherwise the driver strips the "^n" and does not append a newline.
+The IBM 3215 driver behaves similarly.
+
+Pf10 causes the most recent command to be retrieved from the tube's
+command stack (default depth 20) and displayed in the input area.  You
+may hit PF10 again for the next-most-recent command, and so on.  A
+command is entered into the stack only when the input area is not made
+invisible (such as for password entry) and it is not identical to the
+current top entry.  PF10 rotates backward through the command stack;
+PF11 rotates forward.  You may assign the backward function to any PF
+key (or PA key, for that matter), say, PA3, with the command:
+	echo -e pa3=\\033k > /proc/tty/driver/tty3270
+This assigns the string ESC-k to PA3.  Similarly, the string ESC-j
+performs the forward function.  (Rationale:  In bash with vi-mode line
+editing, ESC-k and ESC-j retrieve backward and forward history.
+Suggestions welcome.)
+
+Is a stack size of twenty commands not to your liking?  Change it on
+the fly.  To change to saving the last 100 commands, execute the
+command:
+	echo recallsize=100 > /proc/tty/driver/tty3270
+
+Have a command you issue frequently?  Assign it to a PF or PA key!  Use
+the command
+	echo pf24="mkdir foobar; cd foobar" > /proc/tty/driver/tty3270 
+to execute the commands mkdir foobar and cd foobar immediately when you
+hit PF24.  Want to see the command line first, before you execute it?
+Use the -n option of the echo command:
+	echo -n pf24="mkdir foo; cd foo" > /proc/tty/driver/tty3270
+
+
+
+Happy testing!  I welcome any and all comments about this document, the
+driver, etc etc.
+
+Dick Hitt <rbh00@utsglobal.com>
diff --git a/Documentation/s390/CommonIO b/Documentation/s390/CommonIO
new file mode 100644
index 000000000000..a831d9ae5a5e
--- /dev/null
+++ b/Documentation/s390/CommonIO
@@ -0,0 +1,109 @@
+S/390 common I/O-Layer - command line parameters and /proc entries
+==================================================================
+
+Command line parameters
+-----------------------
+
+* cio_msg = yes | no
+  
+  Determines whether information on found devices and sensed device 
+  characteristics should be shown during startup, i. e. messages of the types 
+  "Detected device 0.0.4711 on subchannel 0.0.0042" and "SenseID: Device
+  0.0.4711 reports: ...".
+
+  Default is off.
+
+
+* cio_ignore = {all} |
+	       {<device> | <range of devices>} |
+	       {!<device> | !<range of devices>}
+
+  The given devices will be ignored by the common I/O-layer; no detection
+  and device sensing will be done on any of those devices. The subchannel to 
+  which the device in question is attached will be treated as if no device was
+  attached.
+
+  An ignored device can be un-ignored later; see the "/proc entries"-section for
+  details.
+
+  The devices must be given either as bus ids (0.0.abcd) or as hexadecimal
+  device numbers (0xabcd or abcd, for 2.4 backward compatibility).
+  You can use the 'all' keyword to ignore all devices.
+  The '!' operator will cause the I/O-layer to _not_ ignore a device.
+  The order on the command line is not important.
+
+  For example, 
+	cio_ignore=0.0.0023-0.0.0042,0.0.4711
+  will ignore all devices ranging from 0.0.0023 to 0.0.0042 and the device
+  0.0.4711, if detected.
+  As another example,
+	cio_ignore=all,!0.0.4711,!0.0.fd00-0.0.fd02
+  will ignore all devices but 0.0.4711, 0.0.fd00, 0.0.fd01, 0.0.fd02.
+
+  By default, no devices are ignored.
+
+
+/proc entries
+-------------
+
+* /proc/cio_ignore
+
+  Lists the ranges of devices (by bus id) which are ignored by common I/O.
+
+  You can un-ignore certain or all devices by piping to /proc/cio_ignore. 
+  "free all" will un-ignore all ignored devices, 
+  "free <device range>, <device range>, ..." will un-ignore the specified
+  devices.
+
+  For example, if devices 0.0.0023 to 0.0.0042 and 0.0.4711 are ignored,
+  - echo free 0.0.0030-0.0.0032 > /proc/cio_ignore
+    will un-ignore devices 0.0.0030 to 0.0.0032 and will leave devices 0.0.0023
+    to 0.0.002f, 0.0.0033 to 0.0.0042 and 0.0.4711 ignored;
+  - echo free 0.0.0041 > /proc/cio_ignore will furthermore un-ignore device
+    0.0.0041;
+  - echo free all > /proc/cio_ignore will un-ignore all remaining ignored 
+    devices.
+
+  When a device is un-ignored, device recognition and sensing is performed and 
+  the device driver will be notified if possible, so the device will become
+  available to the system.
+
+  You can also add ranges of devices to be ignored by piping to 
+  /proc/cio_ignore; "add <device range>, <device range>, ..." will ignore the
+  specified devices.
+
+  Note: Already known devices cannot be ignored.
+
+  For example, if device 0.0.abcd is already known and all other devices
+  0.0.a000-0.0.afff are not known,
+	"echo add 0.0.a000-0.0.accc, 0.0.af00-0.0.afff > /proc/cio_ignore"
+  will add 0.0.a000-0.0.abcc, 0.0.abce-0.0.accc and 0.0.af00-0.0.afff to the
+  list of ignored devices and skip 0.0.abcd.
+
+  The devices can be specified either by bus id (0.0.abcd) or, for 2.4 backward
+  compatibilty, by the device number in hexadecimal (0xabcd or abcd).
+
+
+* /proc/s390dbf/cio_*/ (S/390 debug feature)
+
+  Some views generated by the debug feature to hold various debug outputs.
+
+  - /proc/s390dbf/cio_crw/sprintf
+    Messages from the processing of pending channel report words (machine check
+    handling), which will also show when CONFIG_DEBUG_CRW is defined.
+
+  - /proc/s390dbf/cio_msg/sprintf
+    Various debug messages from the common I/O-layer; generally, messages which 
+    will also show when CONFIG_DEBUG_IO is defined.
+
+  - /proc/s390dbf/cio_trace/hex_ascii
+    Logs the calling of functions in the common I/O-layer and, if applicable, 
+    which subchannel they were called for.
+
+  The level of logging can be changed to be more or less verbose by piping to 
+  /proc/s390dbf/cio_*/level a number between 0 and 6; see the documentation on
+  the S/390 debug feature (Documentation/s390/s390dbf.txt) for details.
+
+* For some of the information present in the /proc filesystem in 2.4 (namely,
+  /proc/subchannels and /proc/chpids), see driver-model.txt.
+  Information formerly in /proc/irq_count is now in /proc/interrupts.
diff --git a/Documentation/s390/DASD b/Documentation/s390/DASD
new file mode 100644
index 000000000000..9963f1e9c98a
--- /dev/null
+++ b/Documentation/s390/DASD
@@ -0,0 +1,73 @@
+DASD device driver
+
+S/390's disk devices (DASDs) are managed by Linux via the DASD device
+driver. It is valid for all types of DASDs and represents them to
+Linux as block devices, namely "dd". Currently the DASD driver uses a
+single major number (254) and 4 minor numbers per volume (1 for the
+physical volume and 3 for partitions). With respect to partitions see
+below. Thus you may have up to 64 DASD devices in your system.
+
+The kernel parameter 'dasd=from-to,...' may be issued arbitrary times
+in the kernel's parameter line or not at all. The 'from' and 'to'
+parameters are to be given in hexadecimal notation without a leading
+0x.
+If you supply kernel parameters the different instances are processed
+in order of appearance and a minor number is reserved for any device
+covered by the supplied range up to 64 volumes. Additional DASDs are
+ignored. If you do not supply the 'dasd=' kernel parameter at all, the 
+DASD driver registers all supported DASDs of your system to a minor
+number in ascending order of the subchannel number.
+
+The driver currently supports ECKD-devices and there are stubs for
+support of the FBA and CKD architectures. For the FBA architecture
+only some smart data structures are missing to make the support
+complete. 
+We performed our testing on 3380 and 3390 type disks of different
+sizes, under VM and on the bare hardware (LPAR), using internal disks
+of the multiprise as well as a RAMAC virtual array. Disks exported by
+an Enterprise Storage Server (Seascape) should work fine as well.
+
+We currently implement one partition per volume, which is the whole
+volume, skipping the first blocks up to the volume label. These are
+reserved for IPL records and IBM's volume label to assure
+accessibility of the DASD from other OSs. In a later stage we will
+provide support of partitions, maybe VTOC oriented or using a kind of
+partition table in the label record.
+
+USAGE
+
+-Low-level format (?CKD only)
+For using an ECKD-DASD as a Linux harddisk you have to low-level
+format the tracks by issuing the BLKDASDFORMAT-ioctl on that
+device. This will erase any data on that volume including IBM volume
+labels, VTOCs etc. The ioctl may take a 'struct format_data *' or
+'NULL' as an argument.  
+typedef struct {
+	int start_unit;
+	int stop_unit;
+	int blksize;
+} format_data_t;
+When a NULL argument is passed to the BLKDASDFORMAT ioctl the whole
+disk is formatted to a blocksize of 1024 bytes. Otherwise start_unit
+and stop_unit are the first and last track to be formatted. If
+stop_unit is -1 it implies that the DASD is formatted from start_unit
+up to the last track. blksize can be any power of two between 512 and
+4096. We recommend no blksize lower than 1024 because the ext2fs uses
+1kB blocks anyway and you gain approx. 50% of capacity increasing your
+blksize from 512 byte to 1kB.
+
+-Make a filesystem
+Then you can mk??fs the filesystem of your choice on that volume or
+partition. For reasons of sanity you should build your filesystem on
+the partition /dev/dd?1 instead of the whole volume. You only lose 3kB	
+but may be sure that you can reuse your data after introduction of a
+real partition table.
+
+BUGS:
+- Performance sometimes is rather low because we don't fully exploit clustering
+
+TODO-List:
+- Add IBM'S Disk layout to genhd
+- Enhance driver to use more than one major number
+- Enable usage as a module
+- Support Cache fast write and DASD fast write (ECKD)
diff --git a/Documentation/s390/Debugging390.txt b/Documentation/s390/Debugging390.txt
new file mode 100644
index 000000000000..adbfe620c061
--- /dev/null
+++ b/Documentation/s390/Debugging390.txt
@@ -0,0 +1,2536 @@
+              
+                          Debugging on Linux for s/390 & z/Architecture
+			               by
+		Denis Joseph Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com)
+		Copyright (C) 2000-2001 IBM Deutschland Entwicklung GmbH, IBM Corporation
+                              Best viewed with fixed width fonts 
+
+Overview of Document:
+=====================
+This document is intended to give an good overview of how to debug 
+Linux for s/390 & z/Architecture it isn't intended as a complete reference & not a
+tutorial on the fundamentals of C & assembly, it dosen't go into
+390 IO in any detail. It is intended to complement the documents in the
+reference section below & any other worthwhile references you get.
+
+It is intended like the Enterprise Systems Architecture/390 Reference Summary
+to be printed out & used as a quick cheat sheet self help style reference when
+problems occur.
+
+Contents
+========
+Register Set
+Address Spaces on Intel Linux
+Address Spaces on Linux for s/390 & z/Architecture
+The Linux for s/390 & z/Architecture Kernel Task Structure
+Register Usage & Stackframes on Linux for s/390 & z/Architecture
+A sample program with comments
+Compiling programs for debugging on Linux for s/390 & z/Architecture
+Figuring out gcc compile errors
+Debugging Tools
+objdump
+strace
+Performance Debugging 
+Debugging under VM
+s/390 & z/Architecture IO Overview
+Debugging IO on s/390 & z/Architecture under VM
+GDB on s/390 & z/Architecture
+Stack chaining in gdb by hand
+Examining core dumps
+ldd
+Debugging modules
+The proc file system
+Starting points for debugging scripting languages etc.
+Dumptool & Lcrash
+SysRq
+References
+Special Thanks
+
+Register Set
+============
+The current architectures have the following registers.
+ 
+16  General propose registers, 32 bit on s/390 64 bit on z/Architecture, r0-r15 or gpr0-gpr15 used for arithmetic & addressing. 
+
+16 Control registers, 32 bit on s/390 64 bit on z/Architecture, ( cr0-cr15 kernel usage only ) used for memory management,
+interrupt control,debugging control etc.
+
+16 Access registers ( ar0-ar15 ) 32 bit on s/390 & z/Architecture
+not used by normal programs but potentially could 
+be used as temporary storage. Their main purpose is their 1 to 1
+association with general purpose registers and are used in
+the kernel for copying data between kernel & user address spaces.
+Access register 0 ( & access register 1 on z/Architecture ( needs 64 bit 
+pointer ) ) is currently used by the pthread library as a pointer to
+the current running threads private area.
+
+16 64 bit floating point registers (fp0-fp15 ) IEEE & HFP floating 
+point format compliant on G5 upwards & a Floating point control reg (FPC) 
+4  64 bit registers (fp0,fp2,fp4 & fp6) HFP only on older machines.
+Note:
+Linux (currently) always uses IEEE & emulates G5 IEEE format on older machines,
+( provided the kernel is configured for this ).
+
+
+The PSW is the most important register on the machine it
+is 64 bit on s/390 & 128 bit on z/Architecture & serves the roles of 
+a program counter (pc), condition code register,memory space designator.
+In IBM standard notation I am counting bit 0 as the MSB.
+It has several advantages over a normal program counter
+in that you can change address translation & program counter 
+in a single instruction. To change address translation,
+e.g. switching address translation off requires that you
+have a logical=physical mapping for the address you are
+currently running at.
+
+      Bit           Value
+s/390 z/Architecture
+0       0     Reserved ( must be 0 ) otherwise specification exception occurs.
+
+1       1     Program Event Recording 1 PER enabled, 
+	      PER is used to facilititate debugging e.g. single stepping.
+
+2-4    2-4    Reserved ( must be 0 ). 
+
+5       5     Dynamic address translation 1=DAT on.
+
+6       6     Input/Output interrupt Mask
+
+7       7     External interrupt Mask used primarily for interprocessor signalling & 
+	      clock interrupts.
+
+8-11  8-11    PSW Key used for complex memory protection mechanism not used under linux
+
+12      12    1 on s/390 0 on z/Architecture
+
+13      13    Machine Check Mask 1=enable machine check interrupts
+
+14      14    Wait State set this to 1 to stop the processor except for interrupts & give 
+	      time to other LPARS used in CPU idle in the kernel to increase overall 
+	      usage of processor resources.
+
+15      15    Problem state ( if set to 1 certain instructions are disabled )
+	      all linux user programs run with this bit 1 
+	      ( useful info for debugging under VM ).
+
+16-17 16-17   Address Space Control
+
+	      00 Primary Space Mode when DAT on
+	      The linux kernel currently runs in this mode, CR1 is affiliated with 
+              this mode & points to the primary segment table origin etc.
+
+	      01 Access register mode this mode is used in functions to 
+	      copy data between kernel & user space.
+
+	      10 Secondary space mode not used in linux however CR7 the
+	      register affiliated with this mode is & this & normally
+	      CR13=CR7 to allow us to copy data between kernel & user space.
+	      We do this as follows:
+	      We set ar2 to 0 to designate its
+	      affiliated gpr ( gpr2 )to point to primary=kernel space.
+	      We set ar4 to 1 to designate its
+	      affiliated gpr ( gpr4 ) to point to secondary=home=user space
+	      & then essentially do a memcopy(gpr2,gpr4,size) to
+	      copy data between the address spaces, the reason we use home space for the
+	      kernel & don't keep secondary space free is that code will not run in 
+	      secondary space.
+
+	      11 Home Space Mode all user programs run in this mode.
+	      it is affiliated with CR13.
+
+18-19 18-19   Condition codes (CC)
+
+20    20      Fixed point overflow mask if 1=FPU exceptions for this event 
+              occur ( normally 0 ) 
+
+21    21      Decimal overflow mask if 1=FPU exceptions for this event occur 
+              ( normally 0 )
+
+22    22      Exponent underflow mask if 1=FPU exceptions for this event occur 
+              ( normally 0 )
+
+23    23      Significance Mask if 1=FPU exceptions for this event occur 
+              ( normally 0 )
+
+24-31 24-30   Reserved Must be 0.
+
+      31      Extended Addressing Mode
+      32      Basic Addressing Mode
+              Used to set addressing mode
+	      PSW 31   PSW 32
+                0         0        24 bit
+                0         1        31 bit
+                1         1        64 bit
+
+32             1=31 bit addressing mode 0=24 bit addressing mode (for backward 
+               compatibility ), linux always runs with this bit set to 1
+
+33-64          Instruction address.
+      33-63    Reserved must be 0
+      64-127   Address
+               In 24 bits mode bits 64-103=0 bits 104-127 Address 
+               In 31 bits mode bits 64-96=0 bits 97-127 Address
+               Note: unlike 31 bit mode on s/390 bit 96 must be zero
+	       when loading the address with LPSWE otherwise a 
+               specification exception occurs, LPSW is fully backward
+               compatible.
+ 	  
+	  
+Prefix Page(s)
+--------------	  
+This per cpu memory area is too intimately tied to the processor not to mention.
+It exists between the real addresses 0-4096 on s/390 & 0-8192 z/Architecture & is exchanged 
+with a 1 page on s/390 or 2 pages on z/Architecture in absolute storage by the set 
+prefix instruction in linux'es startup. 
+This page is mapped to a different prefix for each processor in an SMP configuration
+( assuming the os designer is sane of course :-) ).
+Bytes 0-512 ( 200 hex ) on s/390 & 0-512,4096-4544,4604-5119 currently on z/Architecture 
+are used by the processor itself for holding such information as exception indications & 
+entry points for exceptions.
+Bytes after 0xc00 hex are used by linux for per processor globals on s/390 & z/Architecture 
+( there is a gap on z/Architecure too currently between 0xc00 & 1000 which linux uses ).
+The closest thing to this on traditional architectures is the interrupt
+vector table. This is a good thing & does simplify some of the kernel coding
+however it means that we now cannot catch stray NULL pointers in the
+kernel without hard coded checks.
+
+
+
+Address Spaces on Intel Linux
+=============================
+
+The traditional Intel Linux is approximately mapped as follows forgive
+the ascii art.
+0xFFFFFFFF 4GB Himem                        *****************
+                                            *               *
+                                            * Kernel Space  *
+                                            *               *
+                                            *****************          ****************
+User Space Himem (typically 0xC0000000 3GB )*  User Stack   *          *              *
+				            *****************          *              *
+					    *  Shared Libs  *          * Next Process *          
+                                            *****************          *     to       *  
+					    *               *    <==   *     Run      *  <==
+					    *  User Program *          *              *
+					    *   Data BSS    *          *              *
+                                            *	 Text       *          *              *
+         			            *   Sections    *          *              *
+0x00000000         			    *****************          ****************
+
+Now it is easy to see that on Intel it is quite easy to recognise a kernel address 
+as being one greater than user space himem ( in this case 0xC0000000).
+& addresses of less than this are the ones in the current running program on this
+processor ( if an smp box ).
+If using the virtual machine ( VM ) as a debugger it is quite difficult to
+know which user process is running as the address space you are looking at
+could be from any process in the run queue.
+
+The limitation of Intels addressing technique is that the linux
+kernel uses a very simple real address to virtual addressing technique
+of Real Address=Virtual Address-User Space Himem.
+This means that on Intel the kernel linux can typically only address
+Himem=0xFFFFFFFF-0xC0000000=1GB & this is all the RAM these machines
+can typically use.
+They can lower User Himem to 2GB or lower & thus be
+able to use 2GB of RAM however this shrinks the maximum size
+of User Space from 3GB to 2GB they have a no win limit of 4GB unless
+they go to 64 Bit.
+
+
+On 390 our limitations & strengths make us slightly different.
+For backward compatibility we are only allowed use 31 bits (2GB)
+of our 32 bit addresses,however, we use entirely separate address 
+spaces for the user & kernel.
+
+This means we can support 2GB of non Extended RAM on s/390, & more
+with the Extended memory management swap device & 
+currently 4TB of physical memory currently on z/Architecture.
+
+
+Address Spaces on Linux for s/390 & z/Architecture
+==================================================
+
+Our addressing scheme is as follows
+
+
+Himem 0x7fffffff 2GB on s/390    *****************          ****************
+currently 0x3ffffffffff (2^42)-1 *  User Stack   *          *              *
+on z/Architecture.		 *****************          *              *
+		                 *  Shared Libs  *          *              *      
+                                 *****************          *              *  
+			         *               *          *    Kernel    *  
+		                 *  User Program *          *              *
+		                 *   Data BSS    *          *              *
+                                 *    Text       *          *              *
+            			 *   Sections    *          *              *
+0x00000000                       *****************          ****************
+
+This also means that we need to look at the PSW problem state bit
+or the addressing mode to decide whether we are looking at
+user or kernel space.
+
+Virtual Addresses on s/390 & z/Architecture
+===========================================
+
+A virtual address on s/390 is made up of 3 parts
+The SX ( segment index, roughly corresponding to the PGD & PMD in linux terminology ) 
+being bits 1-11.
+The PX ( page index, corresponding to the page table entry (pte) in linux terminology )
+being bits 12-19. 
+The remaining bits BX (the byte index are the offset in the page )
+i.e. bits 20 to 31.
+
+On z/Architecture in linux we currently make up an address from 4 parts.
+The region index bits (RX) 0-32 we currently use bits 22-32
+The segment index (SX) being bits 33-43
+The page index (PX) being bits  44-51
+The byte index (BX) being bits  52-63
+
+Notes:
+1) s/390 has no PMD so the PMD is really the PGD also.
+A lot of this stuff is defined in pgtable.h.
+
+2) Also seeing as s/390's page indexes are only 1k  in size 
+(bits 12-19 x 4 bytes per pte ) we use 1 ( page 4k )
+to make the best use of memory by updating 4 segment indices 
+entries each time we mess with a PMD & use offsets 
+0,1024,2048 & 3072 in this page as for our segment indexes.
+On z/Architecture our page indexes are now 2k in size
+( bits 12-19 x 8 bytes per pte ) we do a similar trick
+but only mess with 2 segment indices each time we mess with
+a PMD.
+
+3) As z/Architecture supports upto a massive 5-level page table lookup we 
+can only use 3 currently on Linux ( as this is all the generic kernel
+currently supports ) however this may change in future
+this allows us to access ( according to my sums )
+4TB of virtual storage per process i.e.
+4096*512(PTES)*1024(PMDS)*2048(PGD) = 4398046511104 bytes,
+enough for another 2 or 3 of years I think :-).
+to do this we use a region-third-table designation type in
+our address space control registers.
+ 
+
+The Linux for s/390 & z/Architecture Kernel Task Structure
+==========================================================
+Each process/thread under Linux for S390 has its own kernel task_struct
+defined in linux/include/linux/sched.h
+The S390 on initialisation & resuming of a process on a cpu sets
+the __LC_KERNEL_STACK variable in the spare prefix area for this cpu
+( which we use for per processor globals).
+
+The kernel stack pointer is intimately tied with the task stucture for
+each processor as follows.
+
+                      s/390
+            ************************
+            *  1 page kernel stack *
+	    *        ( 4K )        *
+            ************************
+            *   1 page task_struct *        
+            *        ( 4K )        *
+8K aligned  ************************ 
+
+                 z/Architecture
+            ************************
+            *  2 page kernel stack *
+	    *        ( 8K )        *
+            ************************
+            *  2 page task_struct  *        
+            *        ( 8K )        *
+16K aligned ************************ 
+
+What this means is that we don't need to dedicate any register or global variable
+to point to the current running process & can retrieve it with the following
+very simple construct for s/390 & one very similar for z/Architecture.
+
+static inline struct task_struct * get_current(void)
+{
+        struct task_struct *current;
+        __asm__("lhi   %0,-8192\n\t"
+                "nr    %0,15"
+                : "=r" (current) );
+        return current;
+}
+
+i.e. just anding the current kernel stack pointer with the mask -8192.
+Thankfully because Linux dosen't have support for nested IO interrupts
+& our devices have large buffers can survive interrupts being shut for 
+short amounts of time we don't need a separate stack for interrupts.
+
+
+
+
+Register Usage & Stackframes on Linux for s/390 & z/Architecture
+=================================================================
+Overview:
+---------
+This is the code that gcc produces at the top & the bottom of
+each function, it usually is fairly consistent & similar from 
+function to function & if you know its layout you can probalby
+make some headway in finding the ultimate cause of a problem
+after a crash without a source level debugger.
+
+Note: To follow stackframes requires a knowledge of C or Pascal &
+limited knowledge of one assembly language.
+
+It should be noted that there are some differences between the
+s/390 & z/Architecture stack layouts as the z/Architecture stack layout didn't have
+to maintain compatibility with older linkage formats.
+
+Glossary:
+---------
+alloca:
+This is a built in compiler function for runtime allocation
+of extra space on the callers stack which is obviously freed
+up on function exit ( e.g. the caller may choose to allocate nothing
+of a buffer of 4k if required for temporary purposes ), it generates 
+very efficient code ( a few cycles  ) when compared to alternatives 
+like malloc.
+
+automatics: These are local variables on the stack,
+i.e they aren't in registers & they aren't static.
+
+back-chain:
+This is a pointer to the stack pointer before entering a
+framed functions ( see frameless function ) prologue got by 
+deferencing the address of the current stack pointer,
+ i.e. got by accessing the 32 bit value at the stack pointers
+current location.
+
+base-pointer:
+This is a pointer to the back of the literal pool which
+is an area just behind each procedure used to store constants
+in each function.
+
+call-clobbered: The caller probably needs to save these registers if there 
+is something of value in them, on the stack or elsewhere before making a 
+call to another procedure so that it can restore it later.
+
+epilogue:
+The code generated by the compiler to return to the caller.
+
+frameless-function
+A frameless function in Linux for s390 & z/Architecture is one which doesn't 
+need more than the register save area ( 96 bytes on s/390, 160 on z/Architecture )
+given to it by the caller.
+A frameless function never:
+1) Sets up a back chain.
+2) Calls alloca.
+3) Calls other normal functions
+4) Has automatics.
+
+GOT-pointer:
+This is a pointer to the global-offset-table in ELF
+( Executable Linkable Format, Linux'es most common executable format ),
+all globals & shared library objects are found using this pointer.
+
+lazy-binding
+ELF shared libraries are typically only loaded when routines in the shared
+library are actually first called at runtime. This is lazy binding.
+
+procedure-linkage-table
+This is a table found from the GOT which contains pointers to routines
+in other shared libraries which can't be called to by easier means.
+
+prologue:
+The code generated by the compiler to set up the stack frame.
+
+outgoing-args:
+This is extra area allocated on the stack of the calling function if the
+parameters for the callee's cannot all be put in registers, the same
+area can be reused by each function the caller calls.
+
+routine-descriptor:
+A COFF  executable format based concept of a procedure reference 
+actually being 8 bytes or more as opposed to a simple pointer to the routine.
+This is typically defined as follows
+Routine Descriptor offset 0=Pointer to Function
+Routine Descriptor offset 4=Pointer to Table of Contents
+The table of contents/TOC is roughly equivalent to a GOT pointer.
+& it means that shared libraries etc. can be shared between several
+environments each with their own TOC.
+
+ 
+static-chain: This is used in nested functions a concept adopted from pascal 
+by gcc not used in ansi C or C++ ( although quite useful ), basically it
+is a pointer used to reference local variables of enclosing functions.
+You might come across this stuff once or twice in your lifetime.
+
+e.g.
+The function below should return 11 though gcc may get upset & toss warnings 
+about unused variables.
+int FunctionA(int a)
+{
+	int b;
+	FunctionC(int c)
+	{
+		b=c+1;
+	}
+	FunctionC(10);
+	return(b);
+}
+
+
+s/390 & z/Architecture Register usage
+=====================================
+r0       used by syscalls/assembly                  call-clobbered
+r1	 used by syscalls/assembly                  call-clobbered
+r2       argument 0 / return value 0                call-clobbered
+r3       argument 1 / return value 1 (if long long) call-clobbered
+r4       argument 2                                 call-clobbered
+r5       argument 3                                 call-clobbered
+r6	 argument 5                                 saved
+r7       pointer-to arguments 5 to ...              saved      
+r8       this & that                                saved
+r9       this & that                                saved
+r10      static-chain ( if nested function )        saved
+r11      frame-pointer ( if function used alloca )  saved
+r12      got-pointer                                saved
+r13      base-pointer                               saved
+r14      return-address                             saved
+r15      stack-pointer                              saved
+
+f0       argument 0 / return value ( float/double ) call-clobbered
+f2       argument 1                                 call-clobbered
+f4       z/Architecture argument 2                  saved
+f6       z/Architecture argument 3                  saved
+The remaining floating points
+f1,f3,f5 f7-f15 are call-clobbered.
+
+Notes:
+------
+1) The only requirement is that registers which are used
+by the callee are saved, e.g. the compiler is perfectly
+capible of using r11 for purposes other than a frame a
+frame pointer if a frame pointer is not needed.
+2) In functions with variable arguments e.g. printf the calling procedure 
+is identical to one without variable arguments & the same number of 
+parameters. However, the prologue of this function is somewhat more
+hairy owing to it having to move these parameters to the stack to
+get va_start, va_arg & va_end to work.
+3) Access registers are currently unused by gcc but are used in
+the kernel. Possibilities exist to use them at the moment for
+temporary storage but it isn't recommended.
+4) Only 4 of the floating point registers are used for
+parameter passing as older machines such as G3 only have only 4
+& it keeps the stack frame compatible with other compilers.
+However with IEEE floating point emulation under linux on the
+older machines you are free to use the other 12.
+5) A long long or double parameter cannot be have the 
+first 4 bytes in a register & the second four bytes in the 
+outgoing args area. It must be purely in the outgoing args
+area if crossing this boundary.
+6) Floating point parameters are mixed with outgoing args
+on the outgoing args area in the order the are passed in as parameters.
+7) Floating point arguments 2 & 3 are saved in the outgoing args area for 
+z/Architecture
+
+
+Stack Frame Layout
+------------------
+s/390     z/Architecture
+0         0             back chain ( a 0 here signifies end of back chain )
+4         8             eos ( end of stack, not used on Linux for S390 used in other linkage formats )
+8         16            glue used in other s/390 linkage formats for saved routine descriptors etc.
+12        24            glue used in other s/390 linkage formats for saved routine descriptors etc.
+16        32            scratch area
+20        40            scratch area
+24        48            saved r6 of caller function
+28        56            saved r7 of caller function
+32        64            saved r8 of caller function
+36        72            saved r9 of caller function
+40        80            saved r10 of caller function
+44        88            saved r11 of caller function
+48        96            saved r12 of caller function
+52        104           saved r13 of caller function
+56        112           saved r14 of caller function
+60        120           saved r15 of caller function
+64        128           saved f4 of caller function
+72        132           saved f6 of caller function
+80                      undefined
+96        160           outgoing args passed from caller to callee
+96+x      160+x         possible stack alignment ( 8 bytes desirable )
+96+x+y    160+x+y       alloca space of caller ( if used )
+96+x+y+z  160+x+y+z     automatics of caller ( if used )
+0                       back-chain
+
+A sample program with comments.
+===============================
+
+Comments on the function test
+-----------------------------
+1) It didn't need to set up a pointer to the constant pool gpr13 as it isn't used
+( :-( ).
+2) This is a frameless function & no stack is bought.
+3) The compiler was clever enough to recognise that it could return the
+value in r2 as well as use it for the passed in parameter ( :-) ).
+4) The basr ( branch relative & save ) trick works as follows the instruction 
+has a special case with r0,r0 with some instruction operands is understood as 
+the literal value 0, some risc architectures also do this ). So now
+we are branching to the next address & the address new program counter is
+in r13,so now we subtract the size of the function prologue we have executed
++ the size of the literal pool to get to the top of the literal pool
+0040037c int test(int b)
+{                                                          # Function prologue below
+  40037c:	90 de f0 34 	stm	%r13,%r14,52(%r15) # Save registers r13 & r14
+  400380:	0d d0       	basr	%r13,%r0           # Set up pointer to constant pool using
+  400382:	a7 da ff fa 	ahi	%r13,-6            # basr trick
+	return(5+b);
+	                                                   # Huge main program
+  400386:	a7 2a 00 05 	ahi	%r2,5              # add 5 to r2
+
+                                                           # Function epilogue below 
+  40038a:	98 de f0 34 	lm	%r13,%r14,52(%r15) # restore registers r13 & 14
+  40038e:	07 fe       	br	%r14               # return
+}
+
+Comments on the function main
+-----------------------------
+1) The compiler did this function optimally ( 8-) )
+
+Literal pool for main.
+400390:	ff ff ff ec 	.long 0xffffffec
+main(int argc,char *argv[])
+{                                                          # Function prologue below
+  400394:	90 bf f0 2c 	stm	%r11,%r15,44(%r15) # Save necessary registers
+  400398:	18 0f       	lr	%r0,%r15           # copy stack pointer to r0
+  40039a:	a7 fa ff a0 	ahi	%r15,-96           # Make area for callee saving 
+  40039e:	0d d0       	basr	%r13,%r0           # Set up r13 to point to
+  4003a0:	a7 da ff f0 	ahi	%r13,-16           # literal pool
+  4003a4:	50 00 f0 00 	st	%r0,0(%r15)        # Save backchain
+
+	return(test(5));                                   # Main Program Below
+  4003a8:	58 e0 d0 00 	l	%r14,0(%r13)       # load relative address of test from
+						           # literal pool
+  4003ac:	a7 28 00 05 	lhi	%r2,5              # Set first parameter to 5
+  4003b0:	4d ee d0 00 	bas	%r14,0(%r14,%r13)  # jump to test setting r14 as return
+							   # address using branch & save instruction.
+
+							   # Function Epilogue below
+  4003b4:	98 bf f0 8c 	lm	%r11,%r15,140(%r15)# Restore necessary registers.
+  4003b8:	07 fe       	br	%r14               # return to do program exit 
+}
+
+
+Compiler updates
+----------------
+
+main(int argc,char *argv[])
+{
+  4004fc:	90 7f f0 1c       	stm	%r7,%r15,28(%r15)
+  400500:	a7 d5 00 04       	bras	%r13,400508 <main+0xc>
+  400504:	00 40 04 f4       	.long	0x004004f4 
+  # compiler now puts constant pool in code to so it saves an instruction 
+  400508:	18 0f             	lr	%r0,%r15
+  40050a:	a7 fa ff a0       	ahi	%r15,-96
+  40050e:	50 00 f0 00       	st	%r0,0(%r15)
+	return(test(5));
+  400512:	58 10 d0 00       	l	%r1,0(%r13)
+  400516:	a7 28 00 05       	lhi	%r2,5
+  40051a:	0d e1             	basr	%r14,%r1
+  # compiler adds 1 extra instruction to epilogue this is done to
+  # avoid processor pipeline stalls owing to data dependencies on g5 &
+  # above as register 14 in the old code was needed directly after being loaded 
+  # by the lm	%r11,%r15,140(%r15) for the br %14.
+  40051c:	58 40 f0 98       	l	%r4,152(%r15)
+  400520:	98 7f f0 7c       	lm	%r7,%r15,124(%r15)
+  400524:	07 f4             	br	%r4
+}
+
+
+Hartmut ( our compiler developer ) also has been threatening to take out the
+stack backchain in optimised code as this also causes pipeline stalls, you
+have been warned.
+
+64 bit z/Architecture code disassembly
+--------------------------------------
+
+If you understand the stuff above you'll understand the stuff
+below too so I'll avoid repeating myself & just say that 
+some of the instructions have g's on the end of them to indicate
+they are 64 bit & the stack offsets are a bigger, 
+the only other difference you'll find between 32 & 64 bit is that
+we now use f4 & f6 for floating point arguments on 64 bit.
+00000000800005b0 <test>:
+int test(int b)
+{
+	return(5+b);
+    800005b0:	a7 2a 00 05       	ahi	%r2,5
+    800005b4:	b9 14 00 22       	lgfr	%r2,%r2 # downcast to integer
+    800005b8:	07 fe             	br	%r14
+    800005ba:	07 07             	bcr	0,%r7
+
+
+}
+
+00000000800005bc <main>:
+main(int argc,char *argv[])
+{ 
+    800005bc:	eb bf f0 58 00 24 	stmg	%r11,%r15,88(%r15)
+    800005c2:	b9 04 00 1f       	lgr	%r1,%r15
+    800005c6:	a7 fb ff 60       	aghi	%r15,-160
+    800005ca:	e3 10 f0 00 00 24 	stg	%r1,0(%r15)
+	return(test(5));
+    800005d0:	a7 29 00 05       	lghi	%r2,5
+    # brasl allows jumps > 64k & is overkill here bras would do fune
+    800005d4:	c0 e5 ff ff ff ee 	brasl	%r14,800005b0 <test> 
+    800005da:	e3 40 f1 10 00 04 	lg	%r4,272(%r15)
+    800005e0:	eb bf f0 f8 00 04 	lmg	%r11,%r15,248(%r15)
+    800005e6:	07 f4             	br	%r4
+}
+
+
+
+Compiling programs for debugging on Linux for s/390 & z/Architecture
+====================================================================
+-gdwarf-2 now works it should be considered the default debugging
+format for s/390 & z/Architecture as it is more reliable for debugging
+shared libraries,  normal -g debugging works much better now
+Thanks to the IBM java compiler developers bug reports. 
+
+This is typically done adding/appending the flags -g or -gdwarf-2 to the 
+CFLAGS & LDFLAGS variables Makefile of the program concerned.
+
+If using gdb & you would like accurate displays of registers &
+ stack traces compile without optimisation i.e make sure
+that there is no -O2 or similar on the CFLAGS line of the Makefile &
+the emitted gcc commands, obviously this will produce worse code 
+( not advisable for shipment ) but it is an  aid to the debugging process.
+
+This aids debugging because the compiler will copy parameters passed in
+in registers onto the stack so backtracing & looking at passed in
+parameters will work, however some larger programs which use inline functions
+will not compile without optimisation.
+
+Debugging with optimisation has since much improved after fixing
+some bugs, please make sure you are using gdb-5.0 or later developed 
+after Nov'2000.
+
+Figuring out gcc compile errors
+===============================
+If you are getting a lot of syntax errors compiling a program & the problem
+isn't blatantly obvious from the source.
+It often helps to just preprocess the file, this is done with the -E
+option in gcc.
+What this does is that it runs through the very first phase of compilation
+( compilation in gcc is done in several stages & gcc calls many programs to
+achieve its end result ) with the -E option gcc just calls the gcc preprocessor (cpp).
+The c preprocessor does the following, it joins all the files #included together
+recursively ( #include files can #include other files ) & also the c file you wish to compile.
+It puts a fully qualified path of the #included files in a comment & it
+does macro expansion.
+This is useful for debugging because
+1) You can double check whether the files you expect to be included are the ones
+that are being included ( e.g. double check that you aren't going to the i386 asm directory ).
+2) Check that macro definitions aren't clashing with typedefs,
+3) Check that definitons aren't being used before they are being included.
+4) Helps put the line emitting the error under the microscope if it contains macros.
+
+For convenience the Linux kernel's makefile will do preprocessing automatically for you
+by suffixing the file you want built with .i ( instead of .o )
+
+e.g.
+from the linux directory type
+make arch/s390/kernel/signal.i
+this will build
+
+s390-gcc -D__KERNEL__ -I/home1/barrow/linux/include -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
+-fno-strict-aliasing -D__SMP__ -pipe -fno-strength-reduce   -E arch/s390/kernel/signal.c
+> arch/s390/kernel/signal.i  
+
+Now look at signal.i you should see something like.
+
+
+# 1 "/home1/barrow/linux/include/asm/types.h" 1
+typedef unsigned short umode_t;
+typedef __signed__ char __s8;
+typedef unsigned char __u8;
+typedef __signed__ short __s16;
+typedef unsigned short __u16;
+
+If instead you are getting errors further down e.g.
+unknown instruction:2515 "move.l" or better still unknown instruction:2515 
+"Fixme not implemented yet, call Martin" you are probably are attempting to compile some code 
+meant for another architecture or code that is simply not implemented, with a fixme statement
+stuck into the inline assembly code so that the author of the file now knows he has work to do.
+To look at the assembly emitted by gcc just before it is about to call gas ( the gnu assembler )
+use the -S option.
+Again for your convenience the Linux kernel's Makefile will hold your hand &
+do all this donkey work for you also by building the file with the .s suffix.
+e.g.
+from the Linux directory type 
+make arch/s390/kernel/signal.s 
+
+s390-gcc -D__KERNEL__ -I/home1/barrow/linux/include -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
+-fno-strict-aliasing -D__SMP__ -pipe -fno-strength-reduce  -S arch/s390/kernel/signal.c 
+-o arch/s390/kernel/signal.s  
+
+
+This will output something like, ( please note the constant pool & the useful comments
+in the prologue to give you a hand at interpreting it ).
+
+.LC54:
+	.string	"misaligned (__u16 *) in __xchg\n"
+.LC57:
+	.string	"misaligned (__u32 *) in __xchg\n"
+.L$PG1: # Pool sys_sigsuspend
+.LC192:
+	.long	-262401
+.LC193:
+	.long	-1
+.LC194:
+	.long	schedule-.L$PG1
+.LC195:
+	.long	do_signal-.L$PG1
+	.align 4
+.globl sys_sigsuspend
+	.type	 sys_sigsuspend,@function
+sys_sigsuspend:
+#	leaf function           0
+#	automatics              16
+#	outgoing args           0
+#	need frame pointer      0
+#	call alloca             0
+#	has varargs             0
+#	incoming args (stack)   0
+#	function length         168
+	STM	8,15,32(15)
+	LR	0,15
+	AHI	15,-112
+	BASR	13,0
+.L$CO1:	AHI	13,.L$PG1-.L$CO1
+	ST	0,0(15)
+	LR    8,2
+	N     5,.LC192-.L$PG1(13) 
+
+Adding -g to the above output makes the output even more useful
+e.g. typing
+make CC:="s390-gcc -g" kernel/sched.s
+
+which compiles.
+s390-gcc -g -D__KERNEL__ -I/home/barrow/linux-2.3/include -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -fno-strict-aliasing -pipe -fno-strength-reduce   -S kernel/sched.c -o kernel/sched.s 
+
+also outputs stabs ( debugger ) info, from this info you can find out the
+offsets & sizes of various elements in structures.
+e.g. the stab for the structure
+struct rlimit {
+	unsigned long	rlim_cur;
+	unsigned long	rlim_max;
+};
+is
+.stabs "rlimit:T(151,2)=s8rlim_cur:(0,5),0,32;rlim_max:(0,5),32,32;;",128,0,0,0
+from this stab you can see that 
+rlimit_cur starts at bit offset 0 & is 32 bits in size
+rlimit_max starts at bit offset 32 & is 32 bits in size.
+
+
+Debugging Tools:
+================
+
+objdump
+=======
+This is a tool with many options the most useful being ( if compiled with -g).
+objdump --source <victim program or object file> > <victims debug listing >
+
+
+The whole kernel can be compiled like this ( Doing this will make a 17MB kernel
+& a 200 MB listing ) however you have to strip it before building the image
+using the strip command to make it a more reasonable size to boot it.
+
+A source/assembly mixed dump of the kernel can be done with the line
+objdump --source vmlinux > vmlinux.lst
+Also if the file isn't compiled -g this will output as much debugging information
+as it can ( e.g. function names ), however, this is very slow as it spends lots
+of time searching for debugging info, the following self explanitory line should be used 
+instead if the code isn't compiled -g.
+objdump --disassemble-all --syms vmlinux > vmlinux.lst  
+as it is much faster
+
+As hard drive space is valuble most of us use the following approach.
+1) Look at the emitted psw on the console to find the crash address in the kernel.
+2) Look at the file System.map ( in the linux directory ) produced when building 
+the kernel to find the closest address less than the current PSW to find the
+offending function.
+3) use grep or similar to search the source tree looking for the source file
+ with this function if you don't know where it is.
+4) rebuild this object file with -g on, as an example suppose the file was
+( /arch/s390/kernel/signal.o ) 
+5) Assuming the file with the erroneous function is signal.c Move to the base of the 
+Linux source tree.
+6) rm /arch/s390/kernel/signal.o
+7) make /arch/s390/kernel/signal.o
+8) watch the gcc command line emitted
+9) type it in again or alernatively cut & paste it on the console adding the -g option.
+10) objdump --source arch/s390/kernel/signal.o > signal.lst
+This will output the source & the assembly intermixed, as the snippet below shows
+This will unfortunately output addresses which aren't the same
+as the kernel ones you should be able to get around the mental arithmetic
+by playing with the --adjust-vma parameter to objdump.
+
+
+
+
+extern inline void spin_lock(spinlock_t *lp)
+{
+      a0:       18 34           lr      %r3,%r4
+      a2:       a7 3a 03 bc     ahi     %r3,956
+        __asm__ __volatile("    lhi   1,-1\n"
+      a6:       a7 18 ff ff     lhi     %r1,-1
+      aa:       1f 00           slr     %r0,%r0
+      ac:       ba 01 30 00     cs      %r0,%r1,0(%r3)
+      b0:       a7 44 ff fd     jm      aa <sys_sigsuspend+0x2e>
+        saveset = current->blocked;
+      b4:       d2 07 f0 68     mvc     104(8,%r15),972(%r4)
+      b8:       43 cc
+        return (set->sig[0] & mask) != 0;
+} 
+
+6) If debugging under VM go down to that section in the document for more info.
+
+
+I now have a tool which takes the pain out of --adjust-vma
+& you are able to do something like
+make /arch/s390/kernel/traps.lst
+& it automatically generates the correctly relocated entries for
+the text segment in traps.lst.
+This tool is now standard in linux distro's in scripts/makelst
+
+strace:
+-------
+Q. What is it ?
+A. It is a tool for intercepting calls to the kernel & logging them
+to a file & on the screen.
+
+Q. What use is it ?
+A. You can used it to find out what files a particular program opens.
+
+
+
+Example 1
+---------
+If you wanted to know does ping work but didn't have the source 
+strace ping -c 1 127.0.0.1  
+& then look at the man pages for each of the syscalls below,
+( In fact this is sometimes easier than looking at some spagetti
+source which conditionally compiles for several architectures )
+Not everything that it throws out needs to make sense immeadiately
+
+Just looking quickly you can see that it is making up a RAW socket
+for the ICMP protocol.
+Doing an alarm(10) for a 10 second timeout
+& doing a gettimeofday call before & after each read to see 
+how long the replies took, & writing some text to stdout so the user
+has an idea what is going on.
+
+socket(PF_INET, SOCK_RAW, IPPROTO_ICMP) = 3
+getuid()                                = 0
+setuid(0)                               = 0
+stat("/usr/share/locale/C/libc.cat", 0xbffff134) = -1 ENOENT (No such file or directory)
+stat("/usr/share/locale/libc/C", 0xbffff134) = -1 ENOENT (No such file or directory)
+stat("/usr/local/share/locale/C/libc.cat", 0xbffff134) = -1 ENOENT (No such file or directory)
+getpid()                                = 353
+setsockopt(3, SOL_SOCKET, SO_BROADCAST, [1], 4) = 0
+setsockopt(3, SOL_SOCKET, SO_RCVBUF, [49152], 4) = 0
+fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(3, 1), ...}) = 0
+mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40008000
+ioctl(1, TCGETS, {B9600 opost isig icanon echo ...}) = 0
+write(1, "PING 127.0.0.1 (127.0.0.1): 56 d"..., 42PING 127.0.0.1 (127.0.0.1): 56 data bytes
+) = 42
+sigaction(SIGINT, {0x8049ba0, [], SA_RESTART}, {SIG_DFL}) = 0 
+sigaction(SIGALRM, {0x8049600, [], SA_RESTART}, {SIG_DFL}) = 0
+gettimeofday({948904719, 138951}, NULL) = 0
+sendto(3, "\10\0D\201a\1\0\0\17#\2178\307\36"..., 64, 0, {sin_family=AF_INET,
+sin_port=htons(0), sin_addr=inet_addr("127.0.0.1")}, 16) = 64
+sigaction(SIGALRM, {0x8049600, [], SA_RESTART}, {0x8049600, [], SA_RESTART}) = 0
+sigaction(SIGALRM, {0x8049ba0, [], SA_RESTART}, {0x8049600, [], SA_RESTART}) = 0
+alarm(10)                               = 0
+recvfrom(3, "E\0\0T\0005\0\0@\1|r\177\0\0\1\177"..., 192, 0, 
+{sin_family=AF_INET, sin_port=htons(50882), sin_addr=inet_addr("127.0.0.1")}, [16]) = 84
+gettimeofday({948904719, 160224}, NULL) = 0
+recvfrom(3, "E\0\0T\0006\0\0\377\1\275p\177\0"..., 192, 0, 
+{sin_family=AF_INET, sin_port=htons(50882), sin_addr=inet_addr("127.0.0.1")}, [16]) = 84
+gettimeofday({948904719, 166952}, NULL) = 0
+write(1, "64 bytes from 127.0.0.1: icmp_se"..., 
+5764 bytes from 127.0.0.1: icmp_seq=0 ttl=255 time=28.0 ms
+
+Example 2
+---------
+strace passwd 2>&1 | grep open
+produces the following output
+open("/etc/ld.so.cache", O_RDONLY)      = 3
+open("/opt/kde/lib/libc.so.5", O_RDONLY) = -1 ENOENT (No such file or directory)
+open("/lib/libc.so.5", O_RDONLY)        = 3
+open("/dev", O_RDONLY)                  = 3
+open("/var/run/utmp", O_RDONLY)         = 3
+open("/etc/passwd", O_RDONLY)           = 3
+open("/etc/shadow", O_RDONLY)           = 3
+open("/etc/login.defs", O_RDONLY)       = 4
+open("/dev/tty", O_RDONLY)              = 4 
+
+The 2>&1 is done to redirect stderr to stdout & grep is then filtering this input 
+through the pipe for each line containing the string open.
+
+
+Example 3
+---------
+Getting sophistocated
+telnetd crashes on & I don't know why
+Steps
+-----
+1) Replace the following line in /etc/inetd.conf
+telnet  stream  tcp     nowait  root    /usr/sbin/in.telnetd -h 
+with
+telnet  stream  tcp     nowait  root    /blah
+
+2) Create the file /blah with the following contents to start tracing telnetd 
+#!/bin/bash
+/usr/bin/strace -o/t1 -f /usr/sbin/in.telnetd -h 
+3) chmod 700 /blah to make it executable only to root
+4)
+killall -HUP inetd
+or ps aux | grep inetd
+get inetd's process id
+& kill -HUP inetd to restart it.
+
+Important options
+-----------------
+-o is used to tell strace to output to a file in our case t1 in the root directory
+-f is to follow children i.e.
+e.g in our case above telnetd will start the login process & subsequently a shell like bash.
+You will be able to tell which is which from the process ID's listed on the left hand side
+of the strace output.
+-p<pid> will tell strace to attach to a running process, yup this can be done provided
+ it isn't being traced or debugged already & you have enough privileges,
+the reason 2 processes cannot trace or debug the same program is that strace
+becomes the parent process of the one being debugged & processes ( unlike people )
+can have only one parent.
+
+
+However the file /t1 will get big quite quickly
+to test it telnet 127.0.0.1
+
+now look at what files in.telnetd execve'd
+413   execve("/usr/sbin/in.telnetd", ["/usr/sbin/in.telnetd", "-h"], [/* 17 vars */]) = 0
+414   execve("/bin/login", ["/bin/login", "-h", "localhost", "-p"], [/* 2 vars */]) = 0 
+
+Whey it worked!.
+
+
+Other hints:
+------------
+If the program is not very interactive ( i.e. not much keyboard input )
+& is crashing in one architecture but not in another you can do 
+an strace of both programs under as identical a scenario as you can
+on both architectures outputting to a file then.
+do a diff of the two traces using the diff program
+i.e.
+diff output1 output2
+& maybe you'll be able to see where the call paths differed, this
+is possibly near the cause of the crash. 
+
+More info
+---------
+Look at man pages for strace & the various syscalls
+e.g. man strace, man alarm, man socket.
+
+
+Performance Debugging
+=====================
+gcc is capible of compiling in profiling code just add the -p option
+to the CFLAGS, this obviously affects program size & performance.
+This can be used by the gprof gnu profiling tool or the
+gcov the gnu code coverage tool ( code coverage is a means of testing
+code quality by checking if all the code in an executable in exercised by
+a tester ).
+
+
+Using top to find out where processes are sleeping in the kernel
+----------------------------------------------------------------
+To do this copy the System.map from the root directory where
+the linux kernel was built to the /boot directory on your 
+linux machine.
+Start top
+Now type fU<return>
+You should see a new field called WCHAN which
+tells you where each process is sleeping here is a typical output.
+ 
+ 6:59pm  up 41 min,  1 user,  load average: 0.00, 0.00, 0.00
+28 processes: 27 sleeping, 1 running, 0 zombie, 0 stopped
+CPU states:  0.0% user,  0.1% system,  0.0% nice, 99.8% idle
+Mem:   254900K av,   45976K used,  208924K free,       0K shrd,   28636K buff
+Swap:       0K av,       0K used,       0K free                    8620K cached
+
+  PID USER     PRI  NI  SIZE  RSS SHARE WCHAN     STAT  LIB %CPU %MEM   TIME COMMAND
+  750 root      12   0   848  848   700 do_select S       0  0.1  0.3   0:00 in.telnetd
+  767 root      16   0  1140 1140   964           R       0  0.1  0.4   0:00 top
+    1 root       8   0   212  212   180 do_select S       0  0.0  0.0   0:00 init
+    2 root       9   0     0    0     0 down_inte SW      0  0.0  0.0   0:00 kmcheck
+
+The time command
+----------------
+Another related command is the time command which gives you an indication
+of where a process is spending the majority of its time.
+e.g.
+time ping -c 5 nc
+outputs
+real	0m4.054s
+user	0m0.010s
+sys	0m0.010s
+
+Debugging under VM
+==================
+
+Notes
+-----
+Addresses & values in the VM debugger are always hex never decimal
+Address ranges are of the format <HexValue1>-<HexValue2> or <HexValue1>.<HexValue2> 
+e.g. The address range  0x2000 to 0x3000 can be described described as
+2000-3000 or 2000.1000
+
+The VM Debugger is case insensitive.
+
+VM's strengths are usually other debuggers weaknesses you can get at any resource
+no matter how sensitive e.g. memory management resources,change address translation
+in the PSW. For kernel hacking you will reap dividends if you get good at it.
+
+The VM Debugger displays operators but not operands, probably because some
+of it was written when memory was expensive & the programmer was probably proud that
+it fitted into 2k of memory & the programmers & didn't want to shock hardcore VM'ers by
+changing the interface :-), also the debugger displays useful information on the same line & 
+the author of the code probably felt that it was a good idea not to go over 
+the 80 columns on the screen. 
+
+As some of you are probably in a panic now this isn't as unintuitive as it may seem
+as the 390 instructions are easy to decode mentally & you can make a good guess at a lot 
+of them as all the operands are nibble ( half byte aligned ) & if you have an objdump listing
+also it is quite easy to follow, if you don't have an objdump listing keep a copy of
+the s/390 Reference Summary & look at between pages 2 & 7 or alternatively the
+s/390 principles of operation.
+e.g. even I can guess that 
+0001AFF8' LR    180F        CC 0
+is a ( load register ) lr r0,r15 
+
+Also it is very easy to tell the length of a 390 instruction from the 2 most significant
+bits in the instruction ( not that this info is really useful except if you are trying to
+make sense of a hexdump of code ).
+Here is a table
+Bits                    Instruction Length
+------------------------------------------
+00                          2 Bytes
+01                          4 Bytes
+10                          4 Bytes
+11                          6 Bytes
+
+
+
+
+The debugger also displays other useful info on the same line such as the
+addresses being operated on destination addresses of branches & condition codes.
+e.g.  
+00019736' AHI   A7DAFF0E    CC 1
+000198BA' BRC   A7840004 -> 000198C2'   CC 0
+000198CE' STM   900EF068 >> 0FA95E78    CC 2
+
+
+
+Useful VM debugger commands
+---------------------------
+
+I suppose I'd better mention this before I start
+to list the current active traces do 
+Q TR
+there can be a maximum of 255 of these per set
+( more about trace sets later ).
+To stop traces issue a
+TR END.
+To delete a particular breakpoint issue
+TR DEL <breakpoint number>
+
+The PA1 key drops to CP mode so you can issue debugger commands,
+Doing alt c (on my 3270 console at least ) clears the screen. 
+hitting b <enter> comes back to the running operating system
+from cp mode ( in our case linux ).
+It is typically useful to add shortcuts to your profile.exec file
+if you have one ( this is roughly equivalent to autoexec.bat in DOS ).
+file here are a few from mine.
+/* this gives me command history on issuing f12 */
+set pf12 retrieve 
+/* this continues */
+set pf8 imm b
+/* goes to trace set a */
+set pf1 imm tr goto a
+/* goes to trace set b */
+set pf2 imm tr goto b
+/* goes to trace set c */
+set pf3 imm tr goto c
+
+
+
+Instruction Tracing
+-------------------
+Setting a simple breakpoint
+TR I PSWA <address>
+To debug a particular function try
+TR I R <function address range>
+TR I on its own will single step.
+TR I DATA <MNEMONIC> <OPTIONAL RANGE> will trace for particular mnemonics
+e.g.
+TR I DATA 4D R 0197BC.4000
+will trace for BAS'es ( opcode 4D ) in the range 0197BC.4000
+if you were inclined you could add traces for all branch instructions &
+suffix them with the run prefix so you would have a backtrace on screen 
+when a program crashes.
+TR BR <INTO OR FROM> will trace branches into or out of an address.
+e.g.
+TR BR INTO 0 is often quite useful if a program is getting awkward & deciding
+to branch to 0 & crashing as this will stop at the address before in jumps to 0.
+TR I R <address range> RUN cmd d g
+single steps a range of addresses but stays running &
+displays the gprs on each step.
+
+
+
+Displaying & modifying Registers
+--------------------------------
+D G will display all the gprs
+Adding a extra G to all the commands is necessary to access the full 64 bit 
+content in VM on z/Architecture obviously this isn't required for access registers
+as these are still 32 bit.
+e.g. DGG instead of DG 
+D X will display all the control registers
+D AR will display all the access registers
+D AR4-7 will display access registers 4 to 7
+CPU ALL D G will display the GRPS of all CPUS in the configuration
+D PSW will display the current PSW
+st PSW 2000 will put the value 2000 into the PSW &
+cause crash your machine.
+D PREFIX displays the prefix offset
+
+
+Displaying Memory
+-----------------
+To display memory mapped using the current PSW's mapping try
+D <range>
+To make VM display a message each time it hits a particular address & continue try
+D I<range> will disassemble/display a range of instructions.
+ST addr 32 bit word will store a 32 bit aligned address
+D T<range> will display the EBCDIC in an address ( if you are that way inclined )
+D R<range> will display real addresses ( without DAT ) but with prefixing.
+There are other complex options to display if you need to get at say home space
+but are in primary space the easiest thing to do is to temporarily
+modify the PSW to the other addressing mode, display the stuff & then
+restore it.
+
+
+ 
+Hints
+-----
+If you want to issue a debugger command without halting your virtual machine with the
+PA1 key try prefixing the command with #CP e.g.
+#cp tr i pswa 2000
+also suffixing most debugger commands with RUN will cause them not
+to stop just display the mnemonic at the current instruction on the console.
+If you have several breakpoints you want to put into your program &
+you get fed up of cross referencing with System.map
+you can do the following trick for several symbols.
+grep do_signal System.map 
+which emits the following among other things
+0001f4e0 T do_signal 
+now you can do
+
+TR I PSWA 0001f4e0 cmd msg * do_signal
+This sends a message to your own console each time do_signal is entered.
+( As an aside I wrote a perl script once which automatically generated a REXX
+script with breakpoints on every kernel procedure, this isn't a good idea
+because there are thousands of these routines & VM can only set 255 breakpoints
+at a time so you nearly had to spend as long pruning the file down as you would 
+entering the msg's by hand ),however, the trick might be useful for a single object file.
+On linux'es 3270 emulator x3270 there is a very useful option under the file ment
+Save Screens In File this is very good of keeping a copy of traces. 
+
+From CMS help <command name> will give you online help on a particular command. 
+e.g. 
+HELP DISPLAY
+
+Also CP has a file called profile.exec which automatically gets called
+on startup of CMS ( like autoexec.bat ), keeping on a DOS analogy session
+CP has a feature similar to doskey, it may be useful for you to
+use profile.exec to define some keystrokes. 
+e.g.
+SET PF9 IMM B
+This does a single step in VM on pressing F8. 
+SET PF10  ^
+This sets up the ^ key.
+which can be used for ^c (ctrl-c),^z (ctrl-z) which can't be typed directly into some 3270 consoles.
+SET PF11 ^-
+This types the starting keystrokes for a sysrq see SysRq below.
+SET PF12 RETRIEVE
+This retrieves command history on pressing F12.
+
+
+Sometimes in VM the display is set up to scroll automatically this
+can be very annoying if there are messages you wish to look at
+to stop this do
+TERM MORE 255 255
+This will nearly stop automatic screen updates, however it will
+cause a denial of service if lots of messages go to the 3270 console,
+so it would be foolish to use this as the default on a production machine.
+ 
+
+Tracing particular processes
+----------------------------
+The kernel's text segment is intentionally at an address in memory that it will
+very seldom collide with text segments of user programs ( thanks Martin ),
+this simplifies debugging the kernel.
+However it is quite common for user processes to have addresses which collide
+this can make debugging a particular process under VM painful under normal
+circumstances as the process may change when doing a 
+TR I R <address range>.
+Thankfully after reading VM's online help I figured out how to debug
+I particular process.
+
+Your first problem is to find the STD ( segment table designation )
+of the program you wish to debug.
+There are several ways you can do this here are a few
+1) objdump --syms <program to be debugged> | grep main
+To get the address of main in the program.
+tr i pswa <address of main>
+Start the program, if VM drops to CP on what looks like the entry
+point of the main function this is most likely the process you wish to debug.
+Now do a D X13 or D XG13 on z/Architecture.
+On 31 bit the STD is bits 1-19 ( the STO segment table origin ) 
+& 25-31 ( the STL segment table length ) of CR13.
+now type
+TR I R STD <CR13's value> 0.7fffffff
+e.g.
+TR I R STD 8F32E1FF 0.7fffffff
+Another very useful variation is
+TR STORE INTO STD <CR13's value> <address range>
+for finding out when a particular variable changes.
+
+An alternative way of finding the STD of a currently running process 
+is to do the following, ( this method is more complex but
+could be quite convient if you aren't updating the kernel much &
+so your kernel structures will stay constant for a reasonable period of
+time ).
+
+grep task /proc/<pid>/status
+from this you should see something like
+task: 0f160000 ksp: 0f161de8 pt_regs: 0f161f68
+This now gives you a pointer to the task structure.
+Now make CC:="s390-gcc -g" kernel/sched.s
+To get the task_struct stabinfo.
+( task_struct is defined in include/linux/sched.h ).
+Now we want to look at
+task->active_mm->pgd
+on my machine the active_mm in the task structure stab is
+active_mm:(4,12),672,32
+its offset is 672/8=84=0x54
+the pgd member in the mm_struct stab is
+pgd:(4,6)=*(29,5),96,32
+so its offset is 96/8=12=0xc
+
+so we'll
+hexdump -s 0xf160054 /dev/mem | more
+i.e. task_struct+active_mm offset
+to look at the active_mm member
+f160054 0fee cc60 0019 e334 0000 0000 0000 0011
+hexdump -s 0x0feecc6c /dev/mem | more
+i.e. active_mm+pgd offset
+feecc6c 0f2c 0000 0000 0001 0000 0001 0000 0010
+we get something like
+now do 
+TR I R STD <pgd|0x7f> 0.7fffffff
+i.e. the 0x7f is added because the pgd only
+gives the page table origin & we need to set the low bits
+to the maximum possible segment table length.
+TR I R STD 0f2c007f 0.7fffffff
+on z/Architecture you'll probably need to do
+TR I R STD <pgd|0x7> 0.ffffffffffffffff
+to set the TableType to 0x1 & the Table length to 3.
+
+
+
+Tracing Program Exceptions
+--------------------------
+If you get a crash which says something like
+illegal operation or specification exception followed by a register dump
+You can restart linux & trace these using the tr prog <range or value> trace option.
+
+
+
+The most common ones you will normally be tracing for is
+1=operation exception
+2=privileged operation exception
+4=protection exception
+5=addressing exception
+6=specification exception
+10=segment translation exception
+11=page translation exception
+
+The full list of these is on page 22 of the current s/390 Reference Summary.
+e.g.
+tr prog 10 will trace segment translation exceptions.
+tr prog on its own will trace all program interruption codes.
+
+Trace Sets
+----------
+On starting VM you are initially in the INITIAL trace set.
+You can do a Q TR to verify this.
+If you have a complex tracing situation where you wish to wait for instance 
+till a driver is open before you start tracing IO, but know in your
+heart that you are going to have to make several runs through the code till you
+have a clue whats going on. 
+
+What you can do is
+TR I PSWA <Driver open address>
+hit b to continue till breakpoint
+reach the breakpoint
+now do your
+TR GOTO B 
+TR IO 7c08-7c09 inst int run 
+or whatever the IO channels you wish to trace are & hit b
+
+To got back to the initial trace set do
+TR GOTO INITIAL
+& the TR I PSWA <Driver open address> will be the only active breakpoint again.
+
+
+Tracing linux syscalls under VM
+-------------------------------
+Syscalls are implemented on Linux for S390 by the Supervisor call instruction (SVC) there 256 
+possibilities of these as the instruction is made up of a  0xA opcode & the second byte being
+the syscall number. They are traced using the simple command.
+TR SVC  <Optional value or range>
+the syscalls are defined in linux/include/asm-s390/unistd.h
+e.g. to trace all file opens just do
+TR SVC 5 ( as this is the syscall number of open )
+
+
+SMP Specific commands
+---------------------
+To find out how many cpus you have
+Q CPUS displays all the CPU's available to your virtual machine
+To find the cpu that the current cpu VM debugger commands are being directed at do
+Q CPU to change the current cpu cpu VM debugger commands are being directed at do
+CPU <desired cpu no>
+
+On a SMP guest issue a command to all CPUs try prefixing the command with cpu all.
+To issue a command to a particular cpu try cpu <cpu number> e.g.
+CPU 01 TR I R 2000.3000
+If you are running on a guest with several cpus & you have a IO related problem
+& cannot follow the flow of code but you know it isnt smp related.
+from the bash prompt issue
+shutdown -h now or halt.
+do a Q CPUS to find out how many cpus you have
+detach each one of them from cp except cpu 0 
+by issuing a 
+DETACH CPU 01-(number of cpus in configuration)
+& boot linux again.
+TR SIGP will trace inter processor signal processor instructions.
+DEFINE CPU 01-(number in configuration) 
+will get your guests cpus back.
+
+
+Help for displaying ascii textstrings
+-------------------------------------
+On the very latest VM Nucleus'es VM can now display ascii
+( thanks Neale for the hint ) by doing
+D TX<lowaddr>.<len>
+e.g.
+D TX0.100
+
+Alternatively
+=============
+Under older VM debuggers ( I love EBDIC too ) you can use this little program I wrote which
+will convert a command line of hex digits to ascii text which can be compiled under linux & 
+you can copy the hex digits from your x3270 terminal to your xterm if you are debugging
+from a linuxbox.
+
+This is quite useful when looking at a parameter passed in as a text string
+under VM ( unless you are good at decoding ASCII in your head ).
+
+e.g. consider tracing an open syscall
+TR SVC 5
+We have stopped at a breakpoint
+000151B0' SVC   0A05     -> 0001909A'   CC 0
+
+D 20.8 to check the SVC old psw in the prefix area & see was it from userspace
+( for the layout of the prefix area consult P18 of the s/390 390 Reference Summary 
+if you have it available ).
+V00000020  070C2000 800151B2
+The problem state bit wasn't set &  it's also too early in the boot sequence
+for it to be a userspace SVC if it was we would have to temporarily switch the 
+psw to user space addressing so we could get at the first parameter of the open in
+gpr2.
+Next do a 
+D G2
+GPR  2 =  00014CB4
+Now display what gpr2 is pointing to
+D 00014CB4.20
+V00014CB4  2F646576 2F636F6E 736F6C65 00001BF5
+V00014CC4  FC00014C B4001001 E0001000 B8070707
+Now copy the text till the first 00 hex ( which is the end of the string
+to an xterm & do hex2ascii on it.
+hex2ascii 2F646576 2F636F6E 736F6C65 00 
+outputs
+Decoded Hex:=/ d e v / c o n s o l e 0x00 
+We were opening the console device,
+
+You can compile the code below yourself for practice :-),
+/*
+ *    hex2ascii.c
+ *    a useful little tool for converting a hexadecimal command line to ascii
+ *
+ *    Author(s): Denis Joseph Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com)
+ *    (C) 2000 IBM Deutschland Entwicklung GmbH, IBM Corporation.
+ */   
+#include <stdio.h>
+
+int main(int argc,char *argv[])
+{
+  int cnt1,cnt2,len,toggle=0;
+  int startcnt=1;
+  unsigned char c,hex;
+  
+  if(argc>1&&(strcmp(argv[1],"-a")==0))
+     startcnt=2;
+  printf("Decoded Hex:=");
+  for(cnt1=startcnt;cnt1<argc;cnt1++)
+  {
+    len=strlen(argv[cnt1]);
+    for(cnt2=0;cnt2<len;cnt2++)
+    {
+       c=argv[cnt1][cnt2];
+       if(c>='0'&&c<='9')
+	  c=c-'0';
+       if(c>='A'&&c<='F')
+	  c=c-'A'+10;
+       if(c>='a'&&c<='f')
+	  c=c-'a'+10;
+       switch(toggle)
+       {
+	  case 0:
+	     hex=c<<4;
+	     toggle=1;
+	  break;
+	  case 1:
+	     hex+=c;
+	     if(hex<32||hex>127)
+	     {
+		if(startcnt==1)
+		   printf("0x%02X ",(int)hex);
+		else
+		   printf(".");
+	     }
+	     else
+	     {
+	       printf("%c",hex);
+	       if(startcnt==1)
+		  printf(" ");
+	     }
+	     toggle=0;
+	  break;
+       }
+    }
+  }
+  printf("\n");
+}
+
+
+
+
+Stack tracing under VM
+----------------------
+A basic backtrace
+-----------------
+
+Here are the tricks I use 9 out of 10 times it works pretty well,
+
+When your backchain reaches a dead end
+--------------------------------------
+This can happen when an exception happens in the kernel & the kernel is entered twice
+if you reach the NULL pointer at the end of the back chain you should be
+able to sniff further back if you follow the following tricks.
+1) A kernel address should be easy to recognise since it is in
+primary space & the problem state bit isn't set & also
+The Hi bit of the address is set.
+2) Another backchain should also be easy to recognise since it is an 
+address pointing to another address approximately 100 bytes or 0x70 hex
+behind the current stackpointer.
+
+
+Here is some practice.
+boot the kernel & hit PA1 at some random time
+d g to display the gprs, this should display something like
+GPR  0 =  00000001  00156018  0014359C  00000000
+GPR  4 =  00000001  001B8888  000003E0  00000000
+GPR  8 =  00100080  00100084  00000000  000FE000
+GPR 12 =  00010400  8001B2DC  8001B36A  000FFED8
+Note that GPR14 is a return address but as we are real men we are going to
+trace the stack.
+display 0x40 bytes after the stack pointer.
+
+V000FFED8  000FFF38 8001B838 80014C8E 000FFF38
+V000FFEE8  00000000 00000000 000003E0 00000000
+V000FFEF8  00100080 00100084 00000000 000FE000
+V000FFF08  00010400 8001B2DC 8001B36A 000FFED8
+
+
+Ah now look at whats in sp+56 (sp+0x38) this is 8001B36A our saved r14 if
+you look above at our stackframe & also agrees with GPR14.
+
+now backchain 
+d 000FFF38.40
+we now are taking the contents of SP to get our first backchain.
+
+V000FFF38  000FFFA0 00000000 00014995 00147094
+V000FFF48  00147090 001470A0 000003E0 00000000
+V000FFF58  00100080 00100084 00000000 001BF1D0
+V000FFF68  00010400 800149BA 80014CA6 000FFF38
+
+This displays a 2nd return address of 80014CA6
+
+now do d 000FFFA0.40 for our 3rd backchain
+
+V000FFFA0  04B52002 0001107F 00000000 00000000
+V000FFFB0  00000000 00000000 FF000000 0001107F
+V000FFFC0  00000000 00000000 00000000 00000000
+V000FFFD0  00010400 80010802 8001085A 000FFFA0
+
+
+our 3rd return address is 8001085A
+
+as the 04B52002 looks suspiciously like rubbish it is fair to assume that the kernel entry routines
+for the sake of optimisation dont set up a backchain.
+
+now look at System.map to see if the addresses make any sense.
+
+grep -i 0001b3 System.map
+outputs among other things
+0001b304 T cpu_idle 
+so 8001B36A
+is cpu_idle+0x66 ( quiet the cpu is asleep, don't wake it )
+
+
+grep -i 00014 System.map 
+produces among other things
+00014a78 T start_kernel  
+so 0014CA6 is start_kernel+some hex number I can't add in my head.
+
+grep -i 00108 System.map 
+this produces
+00010800 T _stext
+so   8001085A is _stext+0x5a
+
+Congrats you've done your first backchain.
+
+
+
+s/390 & z/Architecture IO Overview
+==================================
+
+I am not going to give a course in 390 IO architecture as this would take me quite a
+while & I'm no expert. Instead I'll give a 390 IO architecture summary for Dummies if you have 
+the s/390 principles of operation available read this instead. If nothing else you may find a few 
+useful keywords in here & be able to use them on a web search engine like altavista to find 
+more useful information.
+
+Unlike other bus architectures modern 390 systems do their IO using mostly
+fibre optics & devices such as tapes & disks can be shared between several mainframes,
+also S390 can support upto 65536 devices while a high end PC based system might be choking 
+with around 64. Here is some of the common IO terminology
+
+Subchannel:
+This is the logical number most IO commands use to talk to an IO device there can be upto
+0x10000 (65536) of these in a configuration typically there is a few hundred. Under VM
+for simplicity they are allocated contiguously, however on the native hardware they are not
+they typically stay consistent between boots provided no new hardware is inserted or removed.
+Under Linux for 390 we use these as IRQ's & also when issuing an IO command (CLEAR SUBCHANNEL,
+HALT SUBCHANNEL,MODIFY SUBCHANNEL,RESUME SUBCHANNEL,START SUBCHANNEL,STORE SUBCHANNEL & 
+TEST SUBCHANNEL ) we use this as the ID of the device we wish to talk to, the most
+important of these instructions are START SUBCHANNEL ( to start IO ), TEST SUBCHANNEL ( to check
+whether the IO completed successfully ), & HALT SUBCHANNEL ( to kill IO ), a subchannel
+can have up to 8 channel paths to a device this offers redunancy if one is not available.
+
+
+Device Number:
+This number remains static & Is closely tied to the hardware, there are 65536 of these
+also they are made up of a CHPID ( Channel Path ID, the most significant 8 bits ) 
+& another lsb 8 bits. These remain static even if more devices are inserted or removed
+from the hardware, there is a 1 to 1 mapping between Subchannels & Device Numbers provided
+devices arent inserted or removed.
+
+Channel Control Words:
+CCWS are linked lists of instructions initially pointed to by an operation request block (ORB),
+which is initially given to Start Subchannel (SSCH) command along with the subchannel number
+for the IO subsystem to process while the CPU continues executing normal code.
+These come in two flavours, Format 0 ( 24 bit for backward )
+compatibility & Format 1 ( 31 bit ). These are typically used to issue read & write 
+( & many other instructions ) they consist of a length field & an absolute address field.
+For each IO typically get 1 or 2 interrupts one for channel end ( primary status ) when the
+channel is idle & the second for device end ( secondary status ) sometimes you get both
+concurrently, you check how the IO went on by issuing a TEST SUBCHANNEL at each interrupt,
+from which you receive an Interruption response block (IRB). If you get channel & device end 
+status in the IRB without channel checks etc. your IO probably went okay. If you didn't you
+probably need a doctorto examine the IRB & extended status word etc.
+If an error occurs more sophistocated control units have a facitity known as
+concurrent sense this means that if an error occurs Extended sense information will
+be presented in the Extended status word in the IRB if not you have to issue a
+subsequent SENSE CCW command after the test subchannel. 
+
+
+TPI( Test pending interrupt) can also be used for polled IO but in multitasking multiprocessor
+systems it isn't recommended except for checking special cases ( i.e. non looping checks for
+pending IO etc. ).
+
+Store Subchannel & Modify Subchannel can be used to examine & modify operating characteristics
+of a subchannel ( e.g. channel paths ).
+
+Other IO related Terms:
+Sysplex: S390's Clustering Technology
+QDIO: S390's new high speed IO architecture to support devices such as gigabit ethernet,
+this architecture is also designed to be forward compatible with up & coming 64 bit machines.
+
+
+General Concepts 
+
+Input Output Processors (IOP's) are responsible for communicating between
+the mainframe CPU's & the channel & relieve the mainframe CPU's from the
+burden of communicating with IO devices directly, this allows the CPU's to 
+concentrate on data processing. 
+
+IOP's can use one or more links ( known as channel paths ) to talk to each 
+IO device. It first checks for path availability & chooses an available one,
+then starts ( & sometimes terminates IO ).
+There are two types of channel path ESCON & the Paralell IO interface.
+
+IO devices are attached to control units, control units provide the
+logic to interface the channel paths & channel path IO protocols to 
+the IO devices, they can be integrated with the devices or housed separately
+& often talk to several similar devices ( typical examples would be raid 
+controllers or a control unit which connects to 1000 3270 terminals ).
+
+
+    +---------------------------------------------------------------+
+    | +-----+ +-----+ +-----+ +-----+  +----------+  +----------+   |
+    | | CPU | | CPU | | CPU | | CPU |  |  Main    |  | Expanded |   |
+    | |     | |     | |     | |     |  |  Memory  |  |  Storage |   |
+    | +-----+ +-----+ +-----+ +-----+  +----------+  +----------+   | 
+    |---------------------------------------------------------------+
+    |   IOP        |      IOP      |       IOP                      |
+    |---------------------------------------------------------------
+    | C | C | C | C | C | C | C | C | C | C | C | C | C | C | C | C | 
+    ----------------------------------------------------------------
+         ||                                              ||
+         ||  Bus & Tag Channel Path                      || ESCON
+         ||  ======================                      || Channel
+         ||  ||                  ||                      || Path
+    +----------+               +----------+         +----------+
+    |          |               |          |         |          |
+    |    CU    |               |    CU    |         |    CU    |
+    |          |               |          |         |          |
+    +----------+               +----------+         +----------+
+       |      |                     |                |       |
++----------+ +----------+      +----------+   +----------+ +----------+
+|I/O Device| |I/O Device|      |I/O Device|   |I/O Device| |I/O Device|
++----------+ +----------+      +----------+   +----------+ +----------+
+  CPU = Central Processing Unit    
+  C = Channel                      
+  IOP = IP Processor               
+  CU = Control Unit
+
+The 390 IO systems come in 2 flavours the current 390 machines support both
+
+The Older 360 & 370 Interface,sometimes called the paralell I/O interface,
+sometimes called Bus-and Tag & sometimes Original Equipment Manufacturers
+Interface (OEMI).
+
+This byte wide paralell channel path/bus has parity & data on the "Bus" cable 
+& control lines on the "Tag" cable. These can operate in byte multiplex mode for
+sharing between several slow devices or burst mode & monopolize the channel for the
+whole burst. Upto 256 devices can be addressed  on one of these cables. These cables are
+about one inch in diameter. The maximum unextended length supported by these cables is
+125 Meters but this can be extended up to 2km with a fibre optic channel extended 
+such as a 3044. The maximum burst speed supported is 4.5 megabytes per second however
+some really old processors support only transfer rates of 3.0, 2.0 & 1.0 MB/sec.
+One of these paths can be daisy chained to up to 8 control units.
+
+
+ESCON if fibre optic it is also called FICON 
+Was introduced by IBM in 1990. Has 2 fibre optic cables & uses either leds or lasers
+for communication at a signaling rate of upto 200 megabits/sec. As 10bits are transferred
+for every 8 bits info this drops to 160 megabits/sec & to 18.6 Megabytes/sec once
+control info & CRC are added. ESCON only operates in burst mode.
+ 
+ESCONs typical max cable length is 3km for the led version & 20km for the laser version
+known as XDF ( extended distance facility ). This can be further extended by using an
+ESCON director which triples the above mentioned ranges. Unlike Bus & Tag as ESCON is
+serial it uses a packet switching architecture the standard Bus & Tag control protocol
+is however present within the packets. Upto 256 devices can be attached to each control 
+unit that uses one of these interfaces.
+
+Common 390 Devices include:
+Network adapters typically OSA2,3172's,2116's & OSA-E gigabit ethernet adapters,
+Consoles 3270 & 3215 ( a teletype emulated under linux for a line mode console ).
+DASD's direct access storage devices ( otherwise known as hard disks ).
+Tape Drives.
+CTC ( Channel to Channel Adapters ),
+ESCON or Paralell Cables used as a very high speed serial link
+between 2 machines. We use 2 cables under linux to do a bi-directional serial link.
+
+
+Debugging IO on s/390 & z/Architecture under VM
+===============================================
+
+Now we are ready to go on with IO tracing commands under VM
+
+A few self explanatory queries:
+Q OSA
+Q CTC
+Q DISK ( This command is CMS specific )
+Q DASD
+
+
+
+
+
+
+Q OSA on my machine returns
+OSA  7C08 ON OSA   7C08 SUBCHANNEL = 0000
+OSA  7C09 ON OSA   7C09 SUBCHANNEL = 0001
+OSA  7C14 ON OSA   7C14 SUBCHANNEL = 0002
+OSA  7C15 ON OSA   7C15 SUBCHANNEL = 0003
+
+If you have a guest with certain priviliges you may be able to see devices
+which don't belong to you to avoid this do add the option V.
+e.g.
+Q V OSA
+
+Now using the device numbers returned by this command we will
+Trace the io starting up on the first device 7c08 & 7c09
+In our simplest case we can trace the 
+start subchannels
+like TR SSCH 7C08-7C09
+or the halt subchannels
+or TR HSCH 7C08-7C09
+MSCH's ,STSCH's I think you can guess the rest
+
+Ingo's favourite trick is tracing all the IO's & CCWS & spooling them into the reader of another
+VM guest so he can ftp the logfile back to his own machine.I'll do a small bit of this & give you
+ a look at the output.
+
+1) Spool stdout to VM reader
+SP PRT TO (another vm guest ) or * for the local vm guest
+2) Fill the reader with the trace
+TR IO 7c08-7c09 INST INT CCW PRT RUN
+3) Start up linux 
+i 00c  
+4) Finish the trace
+TR END
+5) close the reader
+C PRT
+6) list reader contents
+RDRLIST
+7) copy it to linux4's minidisk 
+RECEIVE / LOG TXT A1 ( replace
+8)
+filel & press F11 to look at it
+You should see someting like.
+
+00020942' SSCH  B2334000    0048813C    CC 0    SCH 0000    DEV 7C08
+          CPA 000FFDF0   PARM 00E2C9C4    KEY 0  FPI C0  LPM 80
+          CCW    000FFDF0  E4200100 00487FE8   0000  E4240100 ........
+          IDAL                                      43D8AFE8
+          IDAL                                      0FB76000
+00020B0A'   I/O DEV 7C08 -> 000197BC'   SCH 0000   PARM 00E2C9C4
+00021628' TSCH  B2354000 >> 00488164    CC 0    SCH 0000    DEV 7C08
+          CCWA 000FFDF8   DEV STS 0C  SCH STS 00  CNT 00EC
+           KEY 0   FPI C0  CC 0   CTLS 4007
+00022238' STSCH B2344000 >> 00488108    CC 0    SCH 0000    DEV 7C08
+
+If you don't like messing up your readed ( because you possibly booted from it )
+you can alternatively spool it to another readers guest.
+
+
+Other common VM device related commands
+---------------------------------------------
+These commands are listed only because they have
+been of use to me in the past & may be of use to
+you too. For more complete info on each of the commands
+use type HELP <command> from CMS.
+detaching devices
+DET <devno range>
+ATT <devno range> <guest> 
+attach a device to guest * for your own guest
+READY <devno> cause VM to issue a fake interrupt.
+
+The VARY command is normally only available to VM administrators.
+VARY ON PATH <path> TO <devno range>
+VARY OFF PATH <PATH> FROM <devno range>
+This is used to switch on or off channel paths to devices.
+
+Q CHPID <channel path ID>
+This displays state of devices using this channel path
+D SCHIB <subchannel>
+This displays the subchannel information SCHIB block for the device.
+this I believe is also only available to administrators.
+DEFINE CTC <devno>
+defines a virtual CTC channel to channel connection
+2 need to be defined on each guest for the CTC driver to use.
+COUPLE  devno userid remote devno
+Joins a local virtual device to a remote virtual device
+( commonly used for the CTC driver ).
+
+Building a VM ramdisk under CMS which linux can use
+def vfb-<blocksize> <subchannel> <number blocks>
+blocksize is commonly 4096 for linux.
+Formatting it
+format <subchannel> <driver letter e.g. x> (blksize <blocksize>
+
+Sharing a disk between multiple guests
+LINK userid devno1 devno2 mode password
+
+
+
+GDB on S390
+===========
+N.B. if compiling for debugging gdb works better without optimisation 
+( see Compiling programs for debugging )
+
+invocation
+----------
+gdb <victim program> <optional corefile>
+
+Online help
+-----------
+help: gives help on commands
+e.g.
+help
+help display
+Note gdb's online help is very good use it.
+
+
+Assembly
+--------
+info registers: displays registers other than floating point.
+info all-registers: displays floating points as well.
+disassemble: dissassembles
+e.g.
+disassemble without parameters will disassemble the current function
+disassemble $pc $pc+10 
+
+Viewing & modifying variables
+-----------------------------
+print or p: displays variable or register
+e.g. p/x $sp will display the stack pointer
+
+display: prints variable or register each time program stops
+e.g.
+display/x $pc will display the program counter
+display argc
+
+undisplay : undo's display's
+
+info breakpoints: shows all current breakpoints
+
+info stack: shows stack back trace ( if this dosent work too well, I'll show you the
+stacktrace by hand below ).
+
+info locals: displays local variables.
+
+info args: display current procedure arguments.
+
+set args: will set argc & argv each time the victim program is invoked.
+
+set <variable>=value
+set argc=100
+set $pc=0
+
+
+
+Modifying execution
+-------------------
+step: steps n lines of sourcecode
+step steps 1 line.
+step 100 steps 100 lines of code.
+
+next: like step except this will not step into subroutines
+
+stepi: steps a single machine code instruction.
+e.g. stepi 100
+
+nexti: steps a single machine code instruction but will not step into subroutines.
+
+finish: will run until exit of the current routine
+
+run: (re)starts a program
+
+cont: continues a program
+
+quit: exits gdb.
+
+
+breakpoints
+------------
+
+break
+sets a breakpoint
+e.g.
+
+break main
+
+break *$pc
+
+break *0x400618
+
+heres a really useful one for large programs
+rbr
+Set a breakpoint for all functions matching REGEXP
+e.g.
+rbr 390
+will set a breakpoint with all functions with 390 in their name.
+
+info breakpoints
+lists all breakpoints
+
+delete: delete breakpoint by number or delete them all
+e.g.
+delete 1 will delete the first breakpoint
+delete will delete them all
+
+watch: This will set a watchpoint ( usually hardware assisted ),
+This will watch a variable till it changes
+e.g.
+watch cnt, will watch the variable cnt till it changes.
+As an aside unfortunately gdb's, architecture independent watchpoint code
+is inconsistent & not very good, watchpoints usually work but not always.
+
+info watchpoints: Display currently active watchpoints
+
+condition: ( another useful one )
+Specify breakpoint number N to break only if COND is true.
+Usage is `condition N COND', where N is an integer and COND is an
+expression to be evaluated whenever breakpoint N is reached.
+
+
+
+User defined functions/macros
+-----------------------------
+define: ( Note this is very very useful,simple & powerful )
+usage define <name> <list of commands> end
+
+examples which you should consider putting into .gdbinit in your home directory
+define d
+stepi
+disassemble $pc $pc+10
+end
+
+define e
+nexti
+disassemble $pc $pc+10
+end
+
+
+Other hard to classify stuff
+----------------------------
+signal n:
+sends the victim program a signal.
+e.g. signal 3 will send a SIGQUIT.
+
+info signals:
+what gdb does when the victim receives certain signals.
+
+list:
+e.g.
+list lists current function source
+list 1,10 list first 10 lines of curret file.
+list test.c:1,10
+
+
+directory:
+Adds directories to be searched for source if gdb cannot find the source.
+(note it is a bit sensititive about slashes ) 
+e.g. To add the root of the filesystem to the searchpath do
+directory //
+
+
+call <function>
+This calls a function in the victim program, this is pretty powerful
+e.g.
+(gdb) call printf("hello world")
+outputs:
+$1 = 11 
+
+You might now be thinking that the line above didn't work, something extra had to be done.
+(gdb) call fflush(stdout)
+hello world$2 = 0
+As an aside the debugger also calls malloc & free under the hood 
+to make space for the "hello world" string.
+
+
+
+hints
+-----
+1) command completion works just like bash 
+( if you are a bad typist like me this really helps )
+e.g. hit br <TAB> & cursor up & down :-).
+
+2) if you have a debugging problem that takes a few steps to recreate
+put the steps into a file called .gdbinit in your current working directory
+if you have defined a few extra useful user defined commands put these in 
+your home directory & they will be read each time gdb is launched.
+
+A typical .gdbinit file might be.
+break main
+run
+break runtime_exception
+cont 
+
+
+stack chaining in gdb by hand
+-----------------------------
+This is done using a the same trick described for VM 
+p/x (*($sp+56))&0x7fffffff get the first backchain.
+
+For z/Architecture
+Replace 56 with 112 & ignore the &0x7fffffff
+in the macros below & do nasty casts to longs like the following
+as gdb unfortunately deals with printed arguments as ints which
+messes up everything.
+i.e. here is a 3rd backchain dereference
+p/x *(long *)(***(long ***)$sp+112)
+
+
+this outputs 
+$5 = 0x528f18 
+on my machine.
+Now you can use 
+info symbol (*($sp+56))&0x7fffffff 
+you might see something like.
+rl_getc + 36 in section .text  telling you what is located at address 0x528f18
+Now do.
+p/x (*(*$sp+56))&0x7fffffff 
+This outputs
+$6 = 0x528ed0
+Now do.
+info symbol (*(*$sp+56))&0x7fffffff
+rl_read_key + 180 in section .text
+now do
+p/x (*(**$sp+56))&0x7fffffff
+& so on.
+
+Disassembling instructions without debug info
+---------------------------------------------
+gdb typically compains if there is a lack of debugging
+symbols in  the disassemble command with 
+"No function contains specified address." to get around
+this do 
+x/<number lines to disassemble>xi <address>
+e.g.
+x/20xi 0x400730
+
+
+
+Note: Remember gdb has history just like bash you don't need to retype the
+whole line just use the up & down arrows.
+
+
+
+For more info
+-------------
+From your linuxbox do 
+man gdb or info gdb.
+
+core dumps
+----------
+What a core dump ?,
+A core dump is a file generated by the kernel ( if allowed ) which contains the registers,
+& all active pages of the program which has crashed.
+From this file gdb will allow you to look at the registers & stack trace & memory of the
+program as if it just crashed on your system, it is usually called core & created in the
+current working directory.
+This is very useful in that a customer can mail a core dump to a technical support department
+& the technical support department can reconstruct what happened.
+Provided the have an identical copy of this program with debugging symbols compiled in & 
+the source base of this build is available.
+In short it is far more useful than something like a crash log could ever hope to be.
+
+In theory all that is missing to restart a core dumped program is a kernel patch which
+will do the following.
+1) Make a new kernel task structure
+2) Reload all the dumped pages back into the kernel's memory management structures.
+3) Do the required clock fixups
+4) Get all files & network connections for the process back into an identical state ( really difficult ).
+5) A few more difficult things I haven't thought of.
+
+
+
+Why have I never seen one ?.
+Probably because you haven't used the command 
+ulimit -c unlimited in bash
+to allow core dumps, now do 
+ulimit -a 
+to verify that the limit was accepted.
+
+A sample core dump
+To create this I'm going to do
+ulimit -c unlimited
+gdb 
+to launch gdb (my victim app. ) now be bad & do the following from another 
+telnet/xterm session to the same machine
+ps -aux | grep gdb
+kill -SIGSEGV <gdb's pid>
+or alternatively use killall -SIGSEGV gdb if you have the killall command.
+Now look at the core dump.
+./gdb ./gdb core
+Displays the following
+GNU gdb 4.18
+Copyright 1998 Free Software Foundation, Inc.
+GDB is free software, covered by the GNU General Public License, and you are
+welcome to change it and/or distribute copies of it under certain conditions.
+Type "show copying" to see the conditions.
+There is absolutely no warranty for GDB.  Type "show warranty" for details.
+This GDB was configured as "s390-ibm-linux"...
+Core was generated by `./gdb'.
+Program terminated with signal 11, Segmentation fault.
+Reading symbols from /usr/lib/libncurses.so.4...done.
+Reading symbols from /lib/libm.so.6...done.
+Reading symbols from /lib/libc.so.6...done.
+Reading symbols from /lib/ld-linux.so.2...done.
+#0  0x40126d1a in read () from /lib/libc.so.6
+Setting up the environment for debugging gdb.
+Breakpoint 1 at 0x4dc6f8: file utils.c, line 471.
+Breakpoint 2 at 0x4d87a4: file top.c, line 2609.
+(top-gdb) info stack
+#0  0x40126d1a in read () from /lib/libc.so.6
+#1  0x528f26 in rl_getc (stream=0x7ffffde8) at input.c:402
+#2  0x528ed0 in rl_read_key () at input.c:381
+#3  0x5167e6 in readline_internal_char () at readline.c:454
+#4  0x5168ee in readline_internal_charloop () at readline.c:507
+#5  0x51692c in readline_internal () at readline.c:521
+#6  0x5164fe in readline (prompt=0x7ffff810 "\177�ÿ�øx\177�ÿ�÷�Ø\177�ÿ�øx�À")
+    at readline.c:349
+#7  0x4d7a8a in command_line_input (prrompt=0x564420 "(gdb) ", repeat=1,
+    annotation_suffix=0x4d6b44 "prompt") at top.c:2091
+#8  0x4d6cf0 in command_loop () at top.c:1345
+#9  0x4e25bc in main (argc=1, argv=0x7ffffdf4) at main.c:635
+
+
+LDD
+===
+This is a program which lists the shared libraries which a library needs,
+Note you also get the relocations of the shared library text segments which
+help when using objdump --source.
+e.g.
+ ldd ./gdb
+outputs
+libncurses.so.4 => /usr/lib/libncurses.so.4 (0x40018000)
+libm.so.6 => /lib/libm.so.6 (0x4005e000)
+libc.so.6 => /lib/libc.so.6 (0x40084000)
+/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)
+
+
+Debugging shared libraries
+==========================
+Most programs use shared libraries, however it can be very painful
+when you single step instruction into a function like printf for the 
+first time & you end up in functions like _dl_runtime_resolve this is
+the ld.so doing lazy binding, lazy binding is a concept in ELF where 
+shared library functions are not loaded into memory unless they are 
+actually used, great for saving memory but a pain to debug.
+To get around this either relink the program -static or exit gdb type 
+export LD_BIND_NOW=true this will stop lazy binding & restart the gdb'ing 
+the program in question.
+ 
+
+
+Debugging modules
+=================
+As modules are dynamically loaded into the kernel their address can be
+anywhere to get around this use the -m option with insmod to emit a load
+map which can be piped into a file if required.
+
+The proc file system
+====================
+What is it ?.
+It is a filesystem created by the kernel with files which are created on demand
+by the kernel if read, or can be used to modify kernel parameters,
+it is a powerful concept.
+
+e.g.
+
+cat /proc/sys/net/ipv4/ip_forward 
+On my machine outputs 
+0 
+telling me ip_forwarding is not on to switch it on I can do
+echo 1 >  /proc/sys/net/ipv4/ip_forward
+cat it again
+cat /proc/sys/net/ipv4/ip_forward 
+On my machine now outputs
+1
+IP forwarding is on.
+There is a lot of useful info in here best found by going in & having a look around,
+so I'll take you through some entries I consider important.
+
+All the processes running on the machine have there own entry defined by
+/proc/<pid>
+So lets have a look at the init process
+cd /proc/1
+
+cat cmdline
+emits
+init [2]
+
+cd /proc/1/fd
+This contains numerical entries of all the open files,
+some of these you can cat e.g. stdout (2)
+
+cat /proc/29/maps
+on my machine emits
+
+00400000-00478000 r-xp 00000000 5f:00 4103       /bin/bash
+00478000-0047e000 rw-p 00077000 5f:00 4103       /bin/bash
+0047e000-00492000 rwxp 00000000 00:00 0
+40000000-40015000 r-xp 00000000 5f:00 14382      /lib/ld-2.1.2.so
+40015000-40016000 rw-p 00014000 5f:00 14382      /lib/ld-2.1.2.so
+40016000-40017000 rwxp 00000000 00:00 0
+40017000-40018000 rw-p 00000000 00:00 0
+40018000-4001b000 r-xp 00000000 5f:00 14435      /lib/libtermcap.so.2.0.8
+4001b000-4001c000 rw-p 00002000 5f:00 14435      /lib/libtermcap.so.2.0.8
+4001c000-4010d000 r-xp 00000000 5f:00 14387      /lib/libc-2.1.2.so
+4010d000-40111000 rw-p 000f0000 5f:00 14387      /lib/libc-2.1.2.so
+40111000-40114000 rw-p 00000000 00:00 0
+40114000-4011e000 r-xp 00000000 5f:00 14408      /lib/libnss_files-2.1.2.so
+4011e000-4011f000 rw-p 00009000 5f:00 14408      /lib/libnss_files-2.1.2.so
+7fffd000-80000000 rwxp ffffe000 00:00 0
+
+
+Showing us the shared libraries init uses where they are in memory
+& memory access permissions for each virtual memory area.
+
+/proc/1/cwd is a softlink to the current working directory.
+/proc/1/root is the root of the filesystem for this process. 
+
+/proc/1/mem is the current running processes memory which you
+can read & write to like a file.
+strace uses this sometimes as it is a bit faster than the
+rather inefficent ptrace interface for peeking at DATA.
+
+
+cat status 
+
+Name:   init
+State:  S (sleeping)
+Pid:    1
+PPid:   0
+Uid:    0       0       0       0
+Gid:    0       0       0       0
+Groups:
+VmSize:      408 kB
+VmLck:         0 kB
+VmRSS:       208 kB
+VmData:       24 kB
+VmStk:         8 kB
+VmExe:       368 kB
+VmLib:         0 kB
+SigPnd: 0000000000000000
+SigBlk: 0000000000000000
+SigIgn: 7fffffffd7f0d8fc
+SigCgt: 00000000280b2603
+CapInh: 00000000fffffeff
+CapPrm: 00000000ffffffff
+CapEff: 00000000fffffeff
+
+User PSW:    070de000 80414146
+task: 004b6000 tss: 004b62d8 ksp: 004b7ca8 pt_regs: 004b7f68
+User GPRS:
+00000400  00000000  0000000b  7ffffa90
+00000000  00000000  00000000  0045d9f4
+0045cafc  7ffffa90  7fffff18  0045cb08
+00010400  804039e8  80403af8  7ffff8b0
+User ACRS:
+00000000  00000000  00000000  00000000
+00000001  00000000  00000000  00000000
+00000000  00000000  00000000  00000000
+00000000  00000000  00000000  00000000
+Kernel BackChain  CallChain    BackChain  CallChain
+       004b7ca8   8002bd0c     004b7d18   8002b92c
+       004b7db8   8005cd50     004b7e38   8005d12a
+       004b7f08   80019114                     
+Showing among other things memory usage & status of some signals &
+the processes'es registers from the kernel task_structure
+as well as a backchain which may be useful if a process crashes
+in the kernel for some unknown reason.
+
+Some driver debugging techniques
+================================
+debug feature
+-------------
+Some of our drivers now support a "debug feature" in
+/proc/s390dbf see s390dbf.txt in the linux/Documentation directory
+for more info.
+e.g. 
+to switch on the lcs "debug feature"
+echo 5 > /proc/s390dbf/lcs/level
+& then after the error occurred.
+cat /proc/s390dbf/lcs/sprintf >/logfile
+the logfile now contains some information which may help
+tech support resolve a problem in the field.
+
+
+
+high level debugging network drivers
+------------------------------------
+ifconfig is a quite useful command
+it gives the current state of network drivers.
+
+If you suspect your network device driver is dead
+one way to check is type 
+ifconfig <network device> 
+e.g. tr0
+You should see something like
+tr0       Link encap:16/4 Mbps Token Ring (New)  HWaddr 00:04:AC:20:8E:48
+          inet addr:9.164.185.132  Bcast:9.164.191.255  Mask:255.255.224.0
+          UP BROADCAST RUNNING MULTICAST  MTU:2000  Metric:1
+          RX packets:246134 errors:0 dropped:0 overruns:0 frame:0
+          TX packets:5 errors:0 dropped:0 overruns:0 carrier:0
+          collisions:0 txqueuelen:100
+
+if the device doesn't say up
+try
+/etc/rc.d/init.d/network start 
+( this starts the network stack & hopefully calls ifconfig tr0 up ).
+ifconfig looks at the output of /proc/net/dev & presents it in a more presentable form
+Now ping the device from a machine in the same subnet.
+if the RX packets count & TX packets counts don't increment you probably
+have problems.
+next 
+cat /proc/net/arp
+Do you see any hardware addresses in the cache if not you may have problems.
+Next try
+ping -c 5 <broadcast_addr> i.e. the Bcast field above in the output of
+ifconfig. Do you see any replies from machines other than the local machine
+if not you may have problems. also if the TX packets count in ifconfig
+hasn't incremented either you have serious problems in your driver 
+(e.g. the txbusy field of the network device being stuck on ) 
+or you may have multiple network devices connected.
+
+
+chandev
+-------
+There is a new device layer for channel devices, some
+drivers e.g. lcs are registered with this layer.
+If the device uses the channel device layer you'll be
+able to find what interrupts it uses & the current state 
+of the device.
+See the manpage chandev.8 &type cat /proc/chandev for more info.
+
+
+
+Starting points for debugging scripting languages etc.
+======================================================
+
+bash/sh
+
+bash -x <scriptname>
+e.g. bash -x /usr/bin/bashbug
+displays the following lines as it executes them.
++ MACHINE=i586
++ OS=linux-gnu
++ CC=gcc
++ CFLAGS= -DPROGRAM='bash' -DHOSTTYPE='i586' -DOSTYPE='linux-gnu' -DMACHTYPE='i586-pc-linux-gnu' -DSHELL -DHAVE_CONFIG_H   -I. -I. -I./lib -O2 -pipe
++ RELEASE=2.01
++ PATCHLEVEL=1
++ RELSTATUS=release
++ MACHTYPE=i586-pc-linux-gnu   
+
+perl -d <scriptname> runs the perlscript in a fully intercative debugger
+<like gdb>.
+Type 'h' in the debugger for help.
+
+for debugging java type
+jdb <filename> another fully interactive gdb style debugger.
+& type ? in the debugger for help.
+
+
+
+Dumptool & Lcrash ( lkcd )
+==========================
+Michael Holzheu & others here at IBM have a fairly mature port of 
+SGI's lcrash tool which allows one to look at kernel structures in a
+running kernel.
+
+It also complements a tool called dumptool which dumps all the kernel's
+memory pages & registers to either a tape or a disk.
+This can be used by tech support or an ambitious end user do
+post mortem debugging of a machine like gdb core dumps.
+
+Going into how to use this tool in detail will be explained
+in other documentation supplied by IBM with the patches & the 
+lcrash homepage http://oss.sgi.com/projects/lkcd/ & the lcrash manpage.
+
+How they work
+-------------
+Lcrash is a perfectly normal program,however, it requires 2 
+additional files, Kerntypes which is built using a patch to the 
+linux kernel sources in the linux root directory & the System.map.
+
+Kerntypes is an an objectfile whose sole purpose in life
+is to provide stabs debug info to lcrash, to do this
+Kerntypes is built from kerntypes.c which just includes the most commonly
+referenced header files used when debugging, lcrash can then read the
+.stabs section of this file.
+
+Debugging a live system it uses /dev/mem
+alternatively for post mortem debugging it uses the data 
+collected by dumptool.
+
+
+
+SysRq
+=====
+This is now supported by linux for s/390 & z/Architecture.
+To enable it do compile the kernel with 
+Kernel Hacking -> Magic SysRq Key Enabled
+echo "1" > /proc/sys/kernel/sysrq
+also type
+echo "8" >/proc/sys/kernel/printk
+To make printk output go to console.
+On 390 all commands are prefixed with
+^-
+e.g.
+^-t will show tasks.
+^-? or some unknown command will display help.
+The sysrq key reading is very picky ( I have to type the keys in an
+ xterm session & paste them  into the x3270 console )
+& it may be wise to predefine the keys as described in the VM hints above
+
+This is particularly useful for syncing disks unmounting & rebooting
+if the machine gets partially hung.
+
+Read Documentation/sysrq.txt for more info
+
+References:
+===========
+Enterprise Systems Architecture Reference Summary
+Enterprise Systems Architecture Principles of Operation
+Hartmut Penners s390 stack frame sheet.
+IBM Mainframe Channel Attachment a technology brief from a CISCO webpage
+Various bits of man & info pages of Linux.
+Linux & GDB source.
+Various info & man pages.
+CMS Help on tracing commands.
+Linux for s/390 Elf Application Binary Interface
+Linux for z/Series Elf Application Binary Interface ( Both Highly Recommended )
+z/Architecture Principles of Operation SA22-7832-00
+Enterprise Systems Architecture/390 Reference Summary SA22-7209-01 & the
+Enterprise Systems Architecture/390 Principles of Operation SA22-7201-05
+
+Special Thanks
+==============
+Special thanks to Neale Ferguson who maintains a much
+prettier HTML version of this page at
+http://penguinvm.princeton.edu/notes.html#Debug390
+Bob Grainger Stefan Bader & others for reporting bugs
diff --git a/Documentation/s390/TAPE b/Documentation/s390/TAPE
new file mode 100644
index 000000000000..c639aa5603ff
--- /dev/null
+++ b/Documentation/s390/TAPE
@@ -0,0 +1,122 @@
+Channel attached Tape device driver 
+
+-----------------------------WARNING-----------------------------------------
+This driver is considered to be EXPERIMENTAL. Do NOT use it in 
+production environments. Feel free to test it and report problems back to us. 
+-----------------------------------------------------------------------------
+
+The LINUX for zSeries tape device driver manages channel attached tape drives 
+which are compatible to IBM 3480 or IBM 3490 magnetic tape subsystems. This 
+includes various models of these devices (for example the 3490E). 
+
+
+Tape driver features 
+
+The device driver supports a maximum of 128 tape devices. 
+No official LINUX device major number is assigned to the zSeries tape device 
+driver. It allocates major numbers dynamically and reports them on system 
+startup. 
+Typically it will get major number 254 for both the character device front-end 
+and the block device front-end. 
+
+The tape device driver needs no kernel parameters. All supported devices 
+present are detected on driver initialization at system startup or module load.
+The devices detected are ordered by their subchannel numbers. The device with 
+the lowest subchannel number becomes device 0, the next one will be device 1 
+and so on. 
+
+
+Tape character device front-end 
+
+The usual way to read or write to the tape device is through the character 
+device front-end. The zSeries tape device driver provides two character devices
+for each physical device -- the first of these will rewind automatically when 
+it is closed, the second will not rewind automatically. 
+
+The character device nodes are named /dev/rtibm0 (rewinding) and /dev/ntibm0 
+(non-rewinding) for the first device, /dev/rtibm1 and /dev/ntibm1 for the 
+second, and so on. 
+
+The character device front-end can be used as any other LINUX tape device. You 
+can write to it and read from it using LINUX facilities such as GNU tar. The 
+tool mt can be used to perform control operations, such as rewinding the tape 
+or skipping a file. 
+
+Most LINUX tape software should work with either tape character device. 
+
+
+Tape block device front-end 
+
+The tape device may also be accessed as a block device in read-only mode. 
+This could be used for software installation in the same way as it is used with 
+other operation systems on the zSeries platform (and most LINUX 
+distributions are shipped on compact disk using ISO9660 filesystems). 
+
+One block device node is provided for each physical device. These are named 
+/dev/btibm0 for the first device, /dev/btibm1 for the second and so on. 
+You should only use the ISO9660 filesystem on LINUX for zSeries tapes because 
+the physical tape devices cannot perform fast seeks and the ISO9660 system is 
+optimized for this situation. 
+
+
+Tape block device example 
+
+In this example a tape with an ISO9660 filesystem is created using the first 
+tape device. ISO9660 filesystem support must be built into your system kernel
+for this. 
+The mt command is used to issue tape commands and the mkisofs command to 
+create an ISO9660 filesystem: 
+
+- create a LINUX directory (somedir) with the contents of the filesystem 
+     mkdir somedir
+     cp contents somedir 
+
+- insert a tape 
+
+- ensure the tape is at the beginning 
+     mt -f /dev/ntibm0 rewind 
+
+- set the blocksize of the character driver. The blocksize 2048 bytes
+  is commonly used on ISO9660 CD-Roms
+     mt -f /dev/ntibm0 setblk 2048 
+
+- write the filesystem to the character device driver 
+     mkisofs -o /dev/ntibm0 somedir 
+
+- rewind the tape again 
+     mt -f /dev/ntibm0 rewind 
+
+- Now you can mount your new filesystem as a block device: 
+     mount -t iso9660 -o ro,block=2048 /dev/btibm0 /mnt 
+
+TODO List 
+
+   - Driver has to be stabilized still
+
+BUGS 
+
+This driver is considered BETA, which means some weaknesses may still
+be in it.
+If an error occurs which cannot be handled by the code you will get a 
+sense-data dump.In that case please do the following: 
+
+1. set the tape driver debug level to maximum: 
+     echo 6 >/proc/s390dbf/tape/level 
+
+2. re-perform the actions which produced the bug. (Hopefully the bug will 
+   reappear.) 
+
+3. get a snapshot from the debug-feature: 
+     cat /proc/s390dbf/tape/hex_ascii >somefile 
+
+4. Now put the snapshot together with a detailed description of the situation 
+   that led to the bug: 
+ - Which tool did you use? 
+ - Which hardware do you have? 
+ - Was your tape unit online? 
+ - Is it a shared tape unit? 
+
+5. Send an email with your bug report to: 
+     mailto:Linux390@de.ibm.com 
+
+
diff --git a/Documentation/s390/cds.txt b/Documentation/s390/cds.txt
new file mode 100644
index 000000000000..d9397170fb36
--- /dev/null
+++ b/Documentation/s390/cds.txt
@@ -0,0 +1,513 @@
+Linux for S/390 and zSeries
+
+Common Device Support (CDS)
+Device Driver I/O Support Routines
+
+Authors : Ingo Adlung
+	  Cornelia Huck
+
+Copyright, IBM Corp. 1999-2002
+
+Introduction
+
+This document describes the common device support routines for Linux/390.
+Different than other hardware architectures, ESA/390 has defined a unified
+I/O access method. This gives relief to the device drivers as they don't
+have to deal with different bus types, polling versus interrupt
+processing, shared versus non-shared interrupt processing, DMA versus port
+I/O (PIO), and other hardware features more. However, this implies that
+either every single device driver needs to implement the hardware I/O
+attachment functionality itself, or the operating system provides for a
+unified method to access the hardware, providing all the functionality that
+every single device driver would have to provide itself.
+
+The document does not intend to explain the ESA/390 hardware architecture in
+every detail.This information can be obtained from the ESA/390 Principles of
+Operation manual (IBM Form. No. SA22-7201).
+
+In order to build common device support for ESA/390 I/O interfaces, a
+functional layer was introduced that provides generic I/O access methods to
+the hardware. 
+
+The common device support layer comprises the I/O support routines defined 
+below. Some of them implement common Linux device driver interfaces, while 
+some of them are ESA/390 platform specific.
+
+Note:
+In order to write a driver for S/390, you also need to look into the interface
+described in Documentation/s390/driver-model.txt.
+
+Note for porting drivers from 2.4:
+The major changes are:
+* The functions use a ccw_device instead of an irq (subchannel).
+* All drivers must define a ccw_driver (see driver-model.txt) and the associated
+  functions.
+* request_irq() and free_irq() are no longer done by the driver.
+* The oper_handler is (kindof) replaced by the probe() and set_online() functions
+  of the ccw_driver.
+* The not_oper_handler is (kindof) replaced by the remove() and set_offline()
+  functions of the ccw_driver.
+* The channel device layer is gone.
+* The interrupt handlers must be adapted to use a ccw_device as argument.
+  Moreover, they don't return a devstat, but an irb.
+* Before initiating an io, the options must be set via ccw_device_set_options().
+
+read_dev_chars()	
+   read device characteristics
+   
+read_conf_data()
+   read configuration data.
+
+ccw_device_get_ciw()
+   get commands from extended sense data.
+
+ccw_device_start()	
+   initiate an I/O request.
+
+ccw_device_resume()
+   resume channel program execution.
+
+ccw_device_halt()	
+   terminate the current I/O request processed on the device.
+
+do_IRQ()	
+   generic interrupt routine. This function is called by the interrupt entry
+   routine whenever an I/O interrupt is presented to the system. The do_IRQ()
+   routine determines the interrupt status and calls the device specific
+   interrupt handler according to the rules (flags) defined during I/O request
+   initiation with do_IO().
+
+The next chapters describe the functions other than do_IRQ() in more details.
+The do_IRQ() interface is not described, as it is called from the Linux/390
+first level interrupt handler only and does not comprise a device driver
+callable interface. Instead, the functional description of do_IO() also
+describes the input to the device specific interrupt handler.
+
+Note: All explanations apply also to the 64 bit architecture s390x.
+
+
+Common Device Support (CDS) for Linux/390 Device Drivers
+
+General Information
+
+The following chapters describe the I/O related interface routines the
+Linux/390 common device support (CDS) provides to allow for device specific
+driver implementations on the IBM ESA/390 hardware platform. Those interfaces
+intend to provide the functionality required by every device driver
+implementaion to allow to drive a specific hardware device on the ESA/390
+platform. Some of the interface routines are specific to Linux/390 and some
+of them can be found on other Linux platforms implementations too.
+Miscellaneous function prototypes, data declarations, and macro definitions
+can be found in the architecture specific C header file
+linux/include/asm-s390/irq.h.
+
+Overview of CDS interface concepts
+
+Different to other hardware platforms, the ESA/390 architecture doesn't define
+interrupt lines managed by a specific interrupt controller and bus systems
+that may or may not allow for shared interrupts, DMA processing, etc.. Instead,
+the ESA/390 architecture has implemented a so called channel subsystem, that
+provides a unified view of the devices physically attached to the systems.
+Though the ESA/390 hardware platform knows about a huge variety of different
+peripheral attachments like disk devices (aka. DASDs), tapes, communication
+controllers, etc. they can all by accessed by a well defined access method and
+they are presenting I/O completion a unified way : I/O interruptions. Every
+single device is uniquely identified to the system by a so called subchannel,
+where the ESA/390 architecture allows for 64k devices be attached.
+
+Linux, however, was first built on the Intel PC architecture, with its two
+cascaded 8259 programmable interrupt controllers (PICs), that allow for a
+maximum of 15 different interrupt lines. All devices attached to such a system
+share those 15 interrupt levels. Devices attached to the ISA bus system must
+not share interrupt levels (aka. IRQs), as the ISA bus bases on edge triggered
+interrupts. MCA, EISA, PCI and other bus systems base on level triggered
+interrupts, and therewith allow for shared IRQs. However, if multiple devices
+present their hardware status by the same (shared) IRQ, the operating system
+has to call every single device driver registered on this IRQ in order to
+determine the device driver owning the device that raised the interrupt.
+
+In order not to introduce a new I/O concept to the common Linux code,
+Linux/390 preserves the IRQ concept and semantically maps the ESA/390
+subchannels to Linux as IRQs. This allows Linux/390 to support up to 64k
+different IRQs, uniquely representig a single device each.
+
+Up to kernel 2.4, Linux/390 used to provide interfaces via the IRQ (subchannel).
+For internal use of the common I/O layer, these are still there. However, 
+device drivers should use the new calling interface via the ccw_device only.
+
+During its startup the Linux/390 system checks for peripheral devices. Each
+of those devices is uniquely defined by a so called subchannel by the ESA/390
+channel subsystem. While the subchannel numbers are system generated, each
+subchannel also takes a user defined attribute, the so called device number.
+Both subchannel number and device number can not exceed 65535. During driverfs
+initialisation, the information about control unit type and device types that 
+imply specific I/O commands (channel command words - CCWs) in order to operate
+the device are gathered. Device drivers can retrieve this set of hardware
+information during their initialization step to recognize the devices they
+support using the information saved in the struct ccw_device given to them.
+This methods implies that Linux/390 doesn't require to probe for free (not
+armed) interrupt request lines (IRQs) to drive its devices with. Where
+applicable, the device drivers can use the read_dev_chars() to retrieve device
+characteristics. This can be done without having to request device ownership
+previously.
+
+In order to allow for easy I/O initiation the CDS layer provides a
+ccw_device_start() interface that takes a device specific channel program (one
+or more CCWs) as input sets up the required architecture specific control blocks
+and initiates an I/O request on behalf of the device driver. The
+ccw_device_start() routine allows to specify whether it expects the CDS layer
+to notify the device driver for every interrupt it observes, or with final status
+only. See ccw_device_start() for more details. A device driver must never issue
+ESA/390 I/O commands itself, but must use the Linux/390 CDS interfaces instead.
+
+For long running I/O request to be canceled, the CDS layer provides the
+ccw_device_halt() function. Some devices require to initially issue a HALT
+SUBCHANNEL (HSCH) command without having pending I/O requests. This function is
+also covered by ccw_device_halt().
+
+
+read_dev_chars() - Read Device Characteristics
+
+This routine returns the characteristics for the device specified.
+
+The function is meant to be called with an irq handler in place; that is,
+at earliest during set_online() processing.
+
+While the request is procesed synchronously, the device interrupt
+handler is called for final ending status. In case of error situations the
+interrupt handler may recover appropriately. The device irq handler can
+recognize the corresponding interrupts by the interruption parameter be
+0x00524443.The ccw_device must not be locked prior to calling read_dev_chars().
+
+The function may be called enabled or disabled.
+
+int read_dev_chars(struct ccw_device *cdev, void **buffer, int length );
+
+cdev   - the ccw_device the information is requested for.
+buffer - pointer to a buffer pointer. The buffer pointer itself
+         must contain a valid buffer area.
+length - length of the buffer provided.
+
+The read_dev_chars() function returns :
+
+      0 - successful completion
+-ENODEV - cdev invalid
+-EINVAL - an invalid parameter was detected, or the function was called early.
+-EBUSY  - an irrecoverable I/O error occurred or the device is not
+          operational.
+
+
+read_conf_data() - Read Configuration Data
+
+Retrieve the device dependent configuration data. Please have a look at your 
+device dependent I/O commands for the device specific layout of the node 
+descriptor elements. 
+
+The function is meant to be called with an irq handler in place; that is,
+at earliest during set_online() processing.
+
+The function may be called enabled or disabled, but the device must not be
+locked
+
+int read_conf_data(struct ccw_device, void **buffer, int *length, __u8 lpm);
+
+cdev   - the ccw_device the data is requested for.
+buffer - Pointer to a buffer pointer. The read_conf_data() routine
+         will allocate a buffer and initialize the buffer pointer
+         accordingly. It's the device driver's responsibility to
+         release the kernel memory if no longer needed. 
+length - Length of the buffer allocated and retrieved.
+lpm    - Logical path mask to be used for retrieving the data. If
+         zero the data is retrieved on the next path available.
+
+The read_conf_data() function returns :
+          0 - Successful completion
+-ENODEV     - cdev invalid.
+-EINVAL     - An invalid parameter was detected, or the function was called early.
+-EIO        - An irrecoverable I/O error occurred or the device is
+              not operational.
+-ENOMEM     - The read_conf_data() routine couldn't obtain storage.
+-EOPNOTSUPP - The device doesn't support the read configuration 
+              data command.
+
+
+get_ciw() - get command information word
+
+This call enables a device driver to get information about supported commands
+from the extended SenseID data.
+
+struct ciw *
+ccw_device_get_ciw(struct ccw_device *cdev, __u32 cmd);
+
+cdev - The ccw_device for which the command is to be retrieved.
+cmd  - The command type to be retrieved.
+
+ccw_device_get_ciw() returns:
+NULL    - No extended data available, invalid device or command not found.
+!NULL   - The command requested.
+
+
+ccw_device_start() - Initiate I/O Request
+
+The ccw_device_start() routines is the I/O request front-end processor. All
+device driver I/O requests must be issued using this routine. A device driver
+must not issue ESA/390 I/O commands itself. Instead the ccw_device_start()
+routine provides all interfaces required to drive arbitrary devices.
+
+This description also covers the status information passed to the device
+driver's interrupt handler as this is related to the rules (flags) defined
+with the associated I/O request when calling ccw_device_start().
+
+int ccw_device_start(struct ccw_device *cdev,
+		     struct ccw1 *cpa,
+		     unsigned long intparm,
+		     __u8 lpm,
+		     unsigned long flags);
+
+cdev         : ccw_device the I/O is destined for
+cpa          : logical start address of channel program
+user_intparm : user specific interrupt information; will be presented
+	       back to the device driver's interrupt handler. Allows a
+               device driver to associate the interrupt with a
+               particular I/O request.
+lpm          : defines the channel path to be used for a specific I/O
+               request. A value of 0 will make cio use the opm.
+flag         : defines the action to be performed for I/O processing
+
+Possible flag values are :
+
+DOIO_ALLOW_SUSPEND       - channel program may become suspended
+DOIO_DENY_PREFETCH       - don't allow for CCW prefetch; usually
+                           this implies the channel program might
+                           become modified
+DOIO_SUPPRESS_INTER     - don't call the handler on intermediate status
+
+The cpa parameter points to the first format 1 CCW of a channel program :
+
+struct ccw1 {
+      __u8  cmd_code;/* command code */
+      __u8  flags;   /* flags, like IDA addressing, etc. */
+      __u16 count;   /* byte count */
+      __u32 cda;     /* data address */
+} __attribute__ ((packed,aligned(8)));
+
+with the following CCW flags values defined :
+
+CCW_FLAG_DC        - data chaining
+CCW_FLAG_CC        - command chaining
+CCW_FLAG_SLI       - suppress incorrct length
+CCW_FLAG_SKIP      - skip
+CCW_FLAG_PCI       - PCI
+CCW_FLAG_IDA       - indirect addressing
+CCW_FLAG_SUSPEND   - suspend
+
+
+Via ccw_device_set_options(), the device driver may specify the following
+options for the device:
+
+DOIO_EARLY_NOTIFICATION  - allow for early interrupt notification
+DOIO_REPORT_ALL          - report all interrupt conditions
+
+
+The ccw_device_start() function returns :
+
+      0 - successful completion or request successfully initiated
+-EBUSY  - The device is currently processing a previous I/O request, or ther is
+          a status pending at the device.
+-ENODEV - cdev is invalid, the device is not operational or the ccw_device is
+          not online.
+
+When the I/O request completes, the CDS first level interrupt handler will
+accumalate the status in a struct irb and then call the device interrupt handler.
+The intparm field will contain the value the device driver has associated with a 
+particular I/O request. If a pending device status was recognized, 
+intparm will be set to 0 (zero). This may happen during I/O initiation or delayed
+by an alert status notification. In any case this status is not related to the
+current (last) I/O request. In case of a delayed status notification no special
+interrupt will be presented to indicate I/O completion as the I/O request was
+never started, even though ccw_device_start() returned with successful completion.
+
+If the concurrent sense flag in the extended status word in the irb is set, the
+field irb->scsw.count describes the numer of device specific sense bytes
+available in the extended control word irb->scsw.ecw[0]. No device sensing by
+the device driver itself is required.
+
+The device interrupt handler can use the following definitions to investigate
+the primary unit check source coded in sense byte 0 :
+
+SNS0_CMD_REJECT         0x80
+SNS0_INTERVENTION_REQ   0x40
+SNS0_BUS_OUT_CHECK      0x20
+SNS0_EQUIPMENT_CHECK    0x10
+SNS0_DATA_CHECK         0x08
+SNS0_OVERRUN            0x04
+SNS0_INCOMPL_DOMAIN     0x01
+
+Depending on the device status, multiple of those values may be set together.
+Please refer to the device specific documentation for details.
+
+The irb->scsw.cstat field provides the (accumulated) subchannel status :
+
+SCHN_STAT_PCI            - program controlled interrupt
+SCHN_STAT_INCORR_LEN     - incorrect length
+SCHN_STAT_PROG_CHECK     - program check
+SCHN_STAT_PROT_CHECK     - protection check
+SCHN_STAT_CHN_DATA_CHK   - channel data check
+SCHN_STAT_CHN_CTRL_CHK   - channel control check
+SCHN_STAT_INTF_CTRL_CHK  - interface control check
+SCHN_STAT_CHAIN_CHECK    - chaining check
+
+The irb->scsw.dstat field provides the (accumulated) device status :
+
+DEV_STAT_ATTENTION   - attention
+DEV_STAT_STAT_MOD    - status modifier
+DEV_STAT_CU_END      - control unit end
+DEV_STAT_BUSY        - busy
+DEV_STAT_CHN_END     - channel end
+DEV_STAT_DEV_END     - device end
+DEV_STAT_UNIT_CHECK  - unit check
+DEV_STAT_UNIT_EXCEP  - unit exception
+
+Please see the ESA/390 Principles of Operation manual for details on the
+individual flag meanings.
+
+Usage Notes :
+
+Prior to call ccw_device_start() the device driver must assure disabled state,
+i.e. the I/O mask value in the PSW must be disabled. This can be accomplished
+by calling local_save_flags( flags). The current PSW flags are preserved and
+can be restored by local_irq_restore( flags) at a later time.
+
+If the device driver violates this rule while running in a uni-processor
+environment an interrupt might be presented prior to the ccw_device_start()
+routine returning to the device driver main path. In this case we will end in a
+deadlock situation as the interrupt handler will try to obtain the irq
+lock the device driver still owns (see below) !
+
+The driver must assure to hold the device specific lock. This can be
+accomplished by
+
+(i)  spin_lock(get_ccwdev_lock(cdev)), or
+(ii) spin_lock_irqsave(get_ccwdev_lock(cdev), flags)
+
+Option (i) should be used if the calling routine is running disabled for
+I/O interrupts (see above) already. Option (ii) obtains the device gate und
+puts the CPU into I/O disabled state by preserving the current PSW flags.
+
+The device driver is allowed to issue the next ccw_device_start() call from
+within its interrupt handler already. It is not required to schedule a
+bottom-half, unless an non deterministicly long running error recovery procedure
+or similar needs to be scheduled. During I/O processing the Linux/390 generic
+I/O device driver support has already obtained the IRQ lock, i.e. the handler
+must not try to obtain it again when calling ccw_device_start() or we end in a
+deadlock situation!
+
+If a device driver relies on an I/O request to be completed prior to start the
+next it can reduce I/O processing overhead by chaining a NoOp I/O command
+CCW_CMD_NOOP to the end of the submitted CCW chain. This will force Channel-End
+and Device-End status to be presented together, with a single interrupt.
+However, this should be used with care as it implies the channel will remain
+busy, not being able to process I/O requests for other devices on the same
+channel. Therefore e.g. read commands should never use this technique, as the
+result will be presented by a single interrupt anyway.
+
+In order to minimize I/O overhead, a device driver should use the
+DOIO_REPORT_ALL  only if the device can report intermediate interrupt
+information prior to device-end the device driver urgently relies on. In this
+case all I/O interruptions are presented to the device driver until final
+status is recognized.
+
+If a device is able to recover from asynchronosly presented I/O errors, it can
+perform overlapping I/O using the DOIO_EARLY_NOTIFICATION flag. While some
+devices always report channel-end and device-end together, with a single
+interrupt, others present primary status (channel-end) when the channel is
+ready for the next I/O request and secondary status (device-end) when the data
+transmission has been completed at the device.
+
+Above flag allows to exploit this feature, e.g. for communication devices that
+can handle lost data on the network to allow for enhanced I/O processing.
+
+Unless the channel subsystem at any time presents a secondary status interrupt,
+exploiting this feature will cause only primary status interrupts to be
+presented to the device driver while overlapping I/O is performed. When a
+secondary status without error (alert status) is presented, this indicates
+successful completion for all overlapping ccw_device_start() requests that have
+been issued since the last secondary (final) status.
+
+Channel programs that intend to set the suspend flag on a channel command word 
+(CCW)  must start the I/O operation with the DOIO_ALLOW_SUSPEND option or the 
+suspend flag will cause a channel program check. At the time the channel program 
+becomes suspended an intermediate interrupt will be generated by the channel 
+subsystem.
+
+ccw_device_resume() - Resume Channel Program Execution 
+
+If a device driver chooses to suspend the current channel program execution by 
+setting the CCW suspend flag on a particular CCW, the channel program execution 
+is suspended. In order to resume channel program execution the CIO layer 
+provides the ccw_device_resume() routine. 
+
+int ccw_device_resume(struct ccw_device *cdev);
+
+cdev - ccw_device the resume operation is requested for
+
+The resume_IO() function returns:
+
+        0  - suspended channel program is resumed
+-EBUSY     - status pending
+-ENODEV    - cdev invalid or not-operational subchannel 
+-EINVAL    - resume function not applicable  
+-ENOTCONN  - there is no I/O request pending for completion 
+
+Usage Notes:
+Please have a look at the ccw_device_start() usage notes for more details on
+suspended channel programs.
+
+ccw_device_halt() - Halt I/O Request Processing
+
+Sometimes a device driver might need a possibility to stop the processing of
+a long-running channel program or the device might require to initially issue
+a halt subchannel (HSCH) I/O command. For those purposes the ccw_device_halt()
+command is provided.
+
+int ccw_device_halt(struct ccw_device *cdev,
+                    unsigned long intparm);
+
+cdev    : ccw_device the halt operation is requested for
+intparm : interruption parameter; value is only used if no I/O
+          is outstanding, otherwise the intparm associated with
+          the I/O request is returned
+
+The ccw_device_halt() function returns :
+
+      0 - successful completion or request successfully initiated
+-EBUSY  - the device is currently busy, or status pending.
+-ENODEV - cdev invalid.
+-EINVAL - The device is not operational or the ccw device is not online.
+
+Usage Notes :
+
+A device driver may write a never-ending channel program by writing a channel
+program that at its end loops back to its beginning by means of a transfer in
+channel (TIC)   command (CCW_CMD_TIC). Usually this is performed by network
+device drivers by setting the PCI CCW flag (CCW_FLAG_PCI). Once this CCW is
+executed a program controlled interrupt (PCI) is generated. The device driver
+can then perform an appropriate action. Prior to interrupt of an outstanding
+read to a network device (with or without PCI flag) a ccw_device_halt()
+is required to end the pending operation.
+
+
+Miscellaneous Support Routines
+
+This chapter describes various routines to be used in a Linux/390 device
+driver programming environment.
+
+get_ccwdev_lock()
+
+Get the address of the device specific lock. This is then used in
+spin_lock() / spin_unlock() calls.
+
+
+__u8 ccw_device_get_path_mask(struct ccw_device *cdev);
+
+Get the mask of the path currently available for cdev.
diff --git a/Documentation/s390/config3270.sh b/Documentation/s390/config3270.sh
new file mode 100644
index 000000000000..515e2f431487
--- /dev/null
+++ b/Documentation/s390/config3270.sh
@@ -0,0 +1,76 @@
+#!/bin/sh
+#
+# config3270 -- Autoconfigure /dev/3270/* and /etc/inittab
+#
+#       Usage:
+#               config3270
+#
+#       Output:
+#               /tmp/mkdev3270
+#
+#       Operation:
+#               1. Run this script
+#               2. Run the script it produces: /tmp/mkdev3270
+#               3. Issue "telinit q" or reboot, as appropriate.
+#
+P=/proc/tty/driver/tty3270
+ROOT=
+D=$ROOT/dev
+SUBD=3270
+TTY=$SUBD/tty
+TUB=$SUBD/tub
+SCR=$ROOT/tmp/mkdev3270
+SCRTMP=$SCR.a
+GETTYLINE=:2345:respawn:/sbin/mingetty
+INITTAB=$ROOT/etc/inittab
+NINITTAB=$ROOT/etc/NEWinittab
+OINITTAB=$ROOT/etc/OLDinittab
+ADDNOTE=\\"# Additional mingettys for the 3270/tty* driver, tub3270 ---\\"
+
+if ! ls $P > /dev/null 2>&1; then
+	modprobe tub3270 > /dev/null 2>&1
+fi
+ls $P > /dev/null 2>&1 || exit 1
+
+# Initialize two files, one for /dev/3270 commands and one
+# to replace the /etc/inittab file (old one saved in OLDinittab)
+echo "#!/bin/sh" > $SCR || exit 1
+echo " " >> $SCR
+echo "# Script built by /sbin/config3270" >> $SCR
+if [ ! -d /dev/dasd ]; then
+	echo rm -rf "$D/$SUBD/*" >> $SCR
+fi
+echo "grep -v $TTY $INITTAB > $NINITTAB" > $SCRTMP || exit 1
+echo "echo $ADDNOTE >> $NINITTAB" >> $SCRTMP
+if [ ! -d /dev/dasd ]; then
+	echo mkdir -p $D/$SUBD >> $SCR
+fi
+
+# Now query the tub3270 driver for 3270 device information
+# and add appropriate mknod and mingetty lines to our files
+echo what=config > $P
+while read devno maj min;do
+	if [ $min = 0 ]; then
+		fsmaj=$maj
+		if [ ! -d /dev/dasd ]; then
+			echo mknod $D/$TUB c $fsmaj 0 >> $SCR
+			echo chmod 666 $D/$TUB >> $SCR
+		fi
+	elif [ $maj = CONSOLE ]; then
+		if [ ! -d /dev/dasd ]; then
+			echo mknod $D/$TUB$devno c $fsmaj $min >> $SCR
+		fi
+	else
+		if [ ! -d /dev/dasd ]; then
+			echo mknod $D/$TTY$devno c $maj $min >>$SCR
+			echo mknod $D/$TUB$devno c $fsmaj $min >> $SCR
+		fi
+		echo "echo t$min$GETTYLINE $TTY$devno >> $NINITTAB" >> $SCRTMP
+	fi
+done < $P
+
+echo mv $INITTAB $OINITTAB >> $SCRTMP || exit 1
+echo mv $NINITTAB $INITTAB >> $SCRTMP
+cat $SCRTMP >> $SCR
+rm $SCRTMP
+exit 0
diff --git a/Documentation/s390/crypto/crypto-API.txt b/Documentation/s390/crypto/crypto-API.txt
new file mode 100644
index 000000000000..78a77624a716
--- /dev/null
+++ b/Documentation/s390/crypto/crypto-API.txt
@@ -0,0 +1,83 @@
+crypto-API support for z990 Message Security Assist (MSA) instructions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+AUTHOR:	Thomas Spatzier (tspat@de.ibm.com)
+
+
+1. Introduction crypto-API
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+See Documentation/crypto/api-intro.txt for an introduction/description of the
+kernel crypto API.
+According to api-intro.txt support for z990 crypto instructions has been added
+in the algorithm api layer of the crypto API. Several files containing z990
+optimized implementations of crypto algorithms are placed in the
+arch/s390/crypto directory.
+
+
+2. Probing for availability of MSA
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It should be possible to use Kernels with the z990 crypto implementations both
+on machines with MSA available an on those without MSA (pre z990 or z990
+without MSA). Therefore a simple probing mechanisms has been implemented:
+In the init function of each crypto module the availability of MSA and of the
+respective crypto algorithm in particular will be tested. If the algorithm is
+available the module will load and register its algorithm with the crypto API.
+
+If the respective crypto algorithm is not available, the init function will
+return -ENOSYS. In that case a fallback to the standard software implementation
+of the crypto algorithm must be taken ( -> the standard crypto modules are
+also build when compiling the kernel).
+
+
+3. Ensuring z990 crypto module preference
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+If z990 crypto instructions are available the optimized modules should be
+preferred instead of standard modules.
+
+3.1. compiled-in modules
+~~~~~~~~~~~~~~~~~~~~~~~~
+For compiled-in modules it has to be ensured that the z990 modules are linked
+before the standard crypto modules. Then, on system startup the init functions
+of z990 crypto modules will be called first and query for availability of z990
+crypto instructions. If instruction is available, the z990 module will register
+its crypto algorithm implementation -> the load of the standard module will fail
+since the algorithm is already registered.
+If z990 crypto instruction is not available the load of the z990 module will
+fail -> the standard module will load and register its algorithm.
+
+3.2. dynamic modules
+~~~~~~~~~~~~~~~~~~~~
+A system administrator has to take care of giving preference to z990 crypto
+modules. If MSA is available appropriate lines have to be added to
+/etc/modprobe.conf.
+
+Example:	z990 crypto instruction for SHA1 algorithm is available
+
+		add the following line to /etc/modprobe.conf (assuming the
+		z990 crypto modules for SHA1 is called sha1_z990):
+
+		alias sha1 sha1_z990
+
+		-> when the sha1 algorithm is requested through the crypto API
+		(which has a module autoloader) the z990 module will be loaded.
+
+TBD:	a userspace module probin mechanism
+	something like 'probe sha1 sha1_z990 sha1' in modprobe.conf
+	-> try module sha1_z990, if it fails to load load standard module sha1
+	the 'probe' statement is currently not supported in modprobe.conf
+
+
+4. Currently implemented z990 crypto algorithms
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The following crypto algorithms with z990 MSA support are currently implemented.
+The name of each algorithm under which it is registered in crypto API and the
+name of the respective module is given in square brackets.
+
+- SHA1 Digest Algorithm [sha1 -> sha1_z990]
+- DES Encrypt/Decrypt Algorithm (64bit key) [des -> des_z990]
+- Tripple DES Encrypt/Decrypt Algorithm (128bit key) [des3_ede128 -> des_z990]
+- Tripple DES Encrypt/Decrypt Algorithm (192bit key) [des3_ede -> des_z990]
+
+In order to load, for example, the sha1_z990 module when the sha1 algorithm is
+requested (see 3.2.) add 'alias sha1 sha1_z990' to /etc/modprobe.conf.
+
diff --git a/Documentation/s390/driver-model.txt b/Documentation/s390/driver-model.txt
new file mode 100644
index 000000000000..19461958e2bd
--- /dev/null
+++ b/Documentation/s390/driver-model.txt
@@ -0,0 +1,265 @@
+S/390 driver model interfaces
+-----------------------------
+
+1. CCW devices
+--------------
+
+All devices which can be addressed by means of ccws are called 'CCW devices' -
+even if they aren't actually driven by ccws.
+
+All ccw devices are accessed via a subchannel, this is reflected in the 
+structures under root/:
+
+root/
+     - sys
+     - legacy
+     - css0/
+           - 0.0.0000/0.0.0815/
+	   - 0.0.0001/0.0.4711/
+	   - 0.0.0002/
+	   ...
+
+In this example, device 0815 is accessed via subchannel 0, device 4711 via 
+subchannel 1, and subchannel 2 is a non-I/O subchannel.
+
+You should address a ccw device via its bus id (e.g. 0.0.4711); the device can
+be found under bus/ccw/devices/.
+
+All ccw devices export some data via sysfs.
+
+cutype:	    The control unit type / model.
+
+devtype:    The device type / model, if applicable.
+
+availability: Can be 'good' or 'boxed'; 'no path' or 'no device' for
+	      disconnected devices.
+
+online:     An interface to set the device online and offline.
+	    In the special case of the device being disconnected (see the
+	    notify function under 1.2), piping 0 to online will focibly delete
+	    the device.
+
+The device drivers can add entries to export per-device data and interfaces.
+
+There is also some data exported on a per-subchannel basis (see under
+bus/css/devices/):
+
+chpids:	    Via which chpids the device is connected.
+
+pimpampom:  The path installed, path available and path operational masks.
+
+There also might be additional data, for example for block devices.
+
+
+1.1 Bringing up a ccw device
+----------------------------
+
+This is done in several steps.
+
+a. Each driver can provide one or more parameter interfaces where parameters can
+   be specified. These interfaces are also in the driver's responsibility.
+b. After a. has been performed, if necessary, the device is finally brought up
+   via the 'online' interface.
+
+
+1.2 Writing a driver for ccw devices
+------------------------------------
+
+The basic struct ccw_device and struct ccw_driver data structures can be found
+under include/asm/ccwdev.h.
+
+struct ccw_device {
+        spinlock_t *ccwlock;
+        struct ccw_device_private *private;
+	struct ccw_device_id id;	
+
+	struct ccw_driver *drv;		
+	struct device dev;		
+	int online;
+
+	void (*handler) (struct ccw_device *dev, unsigned long intparm,
+                         struct irb *irb);
+};
+
+struct ccw_driver {
+	struct module *owner;		
+	struct ccw_device_id *ids;	
+	int (*probe) (struct ccw_device *); 
+	int (*remove) (struct ccw_device *);
+	int (*set_online) (struct ccw_device *);
+	int (*set_offline) (struct ccw_device *);
+	int (*notify) (struct ccw_device *, int);
+	struct device_driver driver;
+	char *name;
+};
+
+The 'private' field contains data needed for internal i/o operation only, and
+is not available to the device driver.
+
+Each driver should declare in a MODULE_DEVICE_TABLE into which CU types/models
+and/or device types/models it is interested. This information can later be found
+found in the struct ccw_device_id fields:
+
+struct ccw_device_id {
+	__u16	match_flags;	
+
+	__u16	cu_type;	
+	__u16	dev_type;	
+	__u8	cu_model;	
+	__u8	dev_model;	
+
+	unsigned long driver_info;
+};
+
+The functions in ccw_driver should be used in the following way:
+probe:   This function is called by the device layer for each device the driver
+	 is interested in. The driver should only allocate private structures
+	 to put in dev->driver_data and create attributes (if needed). Also,
+	 the interrupt handler (see below) should be set here.
+
+int (*probe) (struct ccw_device *cdev); 
+
+Parameters:  cdev     - the device to be probed.
+
+
+remove:  This function is called by the device layer upon removal of the driver,
+	 the device or the module. The driver should perform cleanups here.
+
+int (*remove) (struct ccw_device *cdev);
+
+Parameters:   cdev    - the device to be removed.
+
+
+set_online: This function is called by the common I/O layer when the device is
+	    activated via the 'online' attribute. The driver should finally
+	    setup and activate the device here.
+
+int (*set_online) (struct ccw_device *);
+
+Parameters:   cdev	- the device to be activated. The common layer has
+			  verified that the device is not already online.
+
+
+set_offline: This function is called by the common I/O layer when the device is
+	     de-activated via the 'online' attribute. The driver should shut
+	     down the device, but not de-allocate its private data.
+
+int (*set_offline) (struct ccw_device *);
+
+Parameters:   cdev       - the device to be deactivated. The common layer has
+			   verified that the device is online.
+
+
+notify: This function is called by the common I/O layer for some state changes
+	of the device.
+	Signalled to the driver are:
+	* In online state, device detached (CIO_GONE) or last path gone
+	  (CIO_NO_PATH). The driver must return !0 to keep the device; for
+	  return code 0, the device will be deleted as usual (also when no
+	  notify function is registerd). If the driver wants to keep the
+	  device, it is moved into disconnected state.
+	* In disconnected state, device operational again (CIO_OPER). The
+	  common I/O layer performs some sanity checks on device number and
+	  Device / CU to be reasonably sure if it is still the same device.
+	  If not, the old device is removed and a new one registered. By the
+	  return code of the notify function the device driver signals if it
+	  wants the device back: !0 for keeping, 0 to make the device being
+	  removed and re-registered.
+	
+int (*notify) (struct ccw_device *, int);
+
+Parameters:   cdev    - the device whose state changed.
+	      event   - the event that happened. This can be one of CIO_GONE,
+		        CIO_NO_PATH or CIO_OPER.
+
+The handler field of the struct ccw_device is meant to be set to the interrupt
+handler for the device. In order to accommodate drivers which use several 
+distinct handlers (e.g. multi subchannel devices), this is a member of ccw_device
+instead of ccw_driver.
+The handler is registered with the common layer during set_online() processing
+before the driver is called, and is deregistered during set_offline() after the
+driver has been called. Also, after registering / before deregistering, path 
+grouping resp. disbanding of the path group (if applicable) are performed.
+
+void (*handler) (struct ccw_device *dev, unsigned long intparm, struct irb *irb);
+
+Parameters:	dev	- the device the handler is called for
+		intparm - the intparm which allows the device driver to identify
+                          the i/o the interrupt is associated with, or to recognize
+                          the interrupt as unsolicited.
+                irb     - interruption response block which contains the accumulated
+                          status.
+
+The device driver is called from the common ccw_device layer and can retrieve 
+information about the interrupt from the irb parameter.
+
+
+1.3 ccwgroup devices
+--------------------
+
+The ccwgroup mechanism is designed to handle devices consisting of multiple ccw
+devices, like lcs or ctc.
+
+The ccw driver provides a 'group' attribute. Piping bus ids of ccw devices to
+this attributes creates a ccwgroup device consisting of these ccw devices (if
+possible). This ccwgroup device can be set online or offline just like a normal
+ccw device.
+
+Each ccwgroup device also provides an 'ungroup' attribute to destroy the device
+again (only when offline). This is a generic ccwgroup mechanism (the driver does
+not need to implement anything beyond normal removal routines).
+
+To implement a ccwgroup driver, please refer to include/asm/ccwgroup.h. Keep in
+mind that most drivers will need to implement both a ccwgroup and a ccw driver
+(unless you have a meta ccw driver, like cu3088 for lcs and ctc).
+
+
+2. Channel paths
+-----------------
+
+Channel paths show up, like subchannels, under the channel subsystem root (css0)
+and are called 'chp0.<chpid>'. They have no driver and do not belong to any bus.
+Please note, that unlike /proc/chpids in 2.4, the channel path objects reflect
+only the logical state and not the physical state, since we cannot track the
+latter consistently due to lacking machine support (we don't need to be aware
+of anyway).
+
+status - Can be 'online' or 'offline'.
+	 Piping 'on' or 'off' sets the chpid logically online/offline.
+	 Piping 'on' to an online chpid triggers path reprobing for all devices
+	 the chpid connects to. This can be used to force the kernel to re-use
+	 a channel path the user knows to be online, but the machine hasn't
+	 created a machine check for.
+
+
+3. System devices
+-----------------
+
+Note: cpus may yet be added here.
+
+3.1 xpram 
+---------
+
+xpram shows up under sys/ as 'xpram'.
+
+
+4. Other devices
+----------------
+
+4.1 Netiucv
+-----------
+
+The netiucv driver creates an attribute 'connection' under
+bus/iucv/drivers/netiucv. Piping to this attibute creates a new netiucv
+connection to the specified host.
+
+Netiucv connections show up under devices/iucv/ as "netiucv<ifnum>". The interface
+number is assigned sequentially to the connections defined via the 'connection'
+attribute.
+
+user			  - shows the connection partner.
+
+buffer			  - maximum buffer size.
+			    Pipe to it to change buffer size.
+
+
diff --git a/Documentation/s390/monreader.txt b/Documentation/s390/monreader.txt
new file mode 100644
index 000000000000..d843bb04906e
--- /dev/null
+++ b/Documentation/s390/monreader.txt
@@ -0,0 +1,197 @@
+
+Date  : 2004-Nov-26
+Author: Gerald Schaefer (geraldsc@de.ibm.com)
+
+
+             Linux API for read access to z/VM Monitor Records
+             =================================================
+
+
+Description
+===========
+This item delivers a new Linux API in the form of a misc char device that is
+useable from user space and allows read access to the z/VM Monitor Records
+collected by the *MONITOR System Service of z/VM.
+
+
+User Requirements
+=================
+The z/VM guest on which you want to access this API needs to be configured in
+order to allow IUCV connections to the *MONITOR service, i.e. it needs the
+IUCV *MONITOR statement in its user entry. If the monitor DCSS to be used is
+restricted (likely), you also need the NAMESAVE <DCSS NAME> statement.
+This item will use the IUCV device driver to access the z/VM services, so you
+need a kernel with IUCV support. You also need z/VM version 4.4 or 5.1.
+
+There are two options for being able to load the monitor DCSS (examples assume
+that the monitor DCSS begins at 144 MB and ends at 152 MB). You can query the
+location of the monitor DCSS with the Class E privileged CP command Q NSS MAP
+(the values BEGPAG and ENDPAG are given in units of 4K pages).
+
+See also "CP Command and Utility Reference" (SC24-6081-00) for more information
+on the DEF STOR and Q NSS MAP commands, as well as "Saved Segments Planning
+and Administration" (SC24-6116-00) for more information on DCSSes.
+
+1st option:
+-----------
+You can use the CP command DEF STOR CONFIG to define a "memory hole" in your
+guest virtual storage around the address range of the DCSS.
+
+Example: DEF STOR CONFIG 0.140M 200M.200M
+
+This defines two blocks of storage, the first is 140MB in size an begins at
+address 0MB, the second is 200MB in size and begins at address 200MB,
+resulting in a total storage of 340MB. Note that the first block should
+always start at 0 and be at least 64MB in size.
+
+2nd option:
+-----------
+Your guest virtual storage has to end below the starting address of the DCSS
+and you have to specify the "mem=" kernel parameter in your parmfile with a
+value greater than the ending address of the DCSS.
+
+Example: DEF STOR 140M
+
+This defines 140MB storage size for your guest, the parameter "mem=160M" is
+added to the parmfile.
+
+
+User Interface
+==============
+The char device is implemented as a kernel module named "monreader",
+which can be loaded via the modprobe command, or it can be compiled into the
+kernel instead. There is one optional module (or kernel) parameter, "mondcss",
+to specify the name of the monitor DCSS. If the module is compiled into the
+kernel, the kernel parameter "monreader.mondcss=<DCSS NAME>" can be specified
+in the parmfile.
+
+The default name for the DCSS is "MONDCSS" if none is specified. In case that
+there are other users already connected to the *MONITOR service (e.g.
+Performance Toolkit), the monitor DCSS is already defined and you have to use
+the same DCSS. The CP command Q MONITOR (Class E privileged) shows the name
+of the monitor DCSS, if already defined, and the users connected to the
+*MONITOR service.
+Refer to the "z/VM Performance" book (SC24-6109-00) on how to create a monitor
+DCSS if your z/VM doesn't have one already, you need Class E privileges to
+define and save a DCSS.
+
+Example:
+--------
+modprobe monreader mondcss=MYDCSS
+
+This loads the module and sets the DCSS name to "MYDCSS".
+
+NOTE:
+-----
+This API provides no interface to control the *MONITOR service, e.g. specifiy
+which data should be collected. This can be done by the CP command MONITOR
+(Class E privileged), see "CP Command and Utility Reference".
+
+Device nodes with udev:
+-----------------------
+After loading the module, a char device will be created along with the device
+node /<udev directory>/monreader.
+
+Device nodes without udev:
+--------------------------
+If your distribution does not support udev, a device node will not be created
+automatically and you have to create it manually after loading the module.
+Therefore you need to know the major and minor numbers of the device. These
+numbers can be found in /sys/class/misc/monreader/dev.
+Typing cat /sys/class/misc/monreader/dev will give an output of the form
+<major>:<minor>. The device node can be created via the mknod command, enter
+mknod <name> c <major> <minor>, where <name> is the name of the device node
+to be created.
+
+Example:
+--------
+# modprobe monreader
+# cat /sys/class/misc/monreader/dev
+10:63
+# mknod /dev/monreader c 10 63
+
+This loads the module with the default monitor DCSS (MONDCSS) and creates a
+device node.
+
+File operations:
+----------------
+The following file operations are supported: open, release, read, poll.
+There are two alternative methods for reading: either non-blocking read in
+conjunction with polling, or blocking read without polling. IOCTLs are not
+supported.
+
+Read:
+-----
+Reading from the device provides a 12 Byte monitor control element (MCE),
+followed by a set of one or more contiguous monitor records (similar to the
+output of the CMS utility MONWRITE without the 4K control blocks). The MCE
+contains information on the type of the following record set (sample/event
+data), the monitor domains contained within it and the start and end address
+of the record set in the monitor DCSS. The start and end address can be used
+to determine the size of the record set, the end address is the address of the
+last byte of data. The start address is needed to handle "end-of-frame" records
+correctly (domain 1, record 13), i.e. it can be used to determine the record
+start offset relative to a 4K page (frame) boundary.
+
+See "Appendix A: *MONITOR" in the "z/VM Performance" document for a description
+of the monitor control element layout. The layout of the monitor records can
+be found here (z/VM 5.1): http://www.vm.ibm.com/pubs/mon510/index.html
+
+The layout of the data stream provided by the monreader device is as follows:
+...
+<0 byte read>
+<first MCE>              \
+<first set of records>    |
+...                       |- data set
+<last MCE>                |
+<last set of records>    /
+<0 byte read>
+...
+
+There may be more than one combination of MCE and corresponding record set
+within one data set and the end of each data set is indicated by a successful
+read with a return value of 0 (0 byte read).
+Any received data must be considered invalid until a complete set was
+read successfully, including the closing 0 byte read. Therefore you should
+always read the complete set into a buffer before processing the data.
+
+The maximum size of a data set can be as large as the size of the
+monitor DCSS, so design the buffer adequately or use dynamic memory allocation.
+The size of the monitor DCSS will be printed into syslog after loading the
+module. You can also use the (Class E privileged) CP command Q NSS MAP to
+list all available segments and information about them.
+
+As with most char devices, error conditions are indicated by returning a
+negative value for the number of bytes read. In this case, the errno variable
+indicates the error condition:
+
+EIO: reply failed, read data is invalid and the application
+     should discard the data read since the last successful read with 0 size.
+EFAULT: copy_to_user failed, read data is invalid and the application should
+        discard the data read since the last successful read with 0 size.
+EAGAIN: occurs on a non-blocking read if there is no data available at the
+        moment. There is no data missing or corrupted, just try again or rather
+        use polling for non-blocking reads.
+EOVERFLOW: message limit reached, the data read since the last successful
+           read with 0 size is valid but subsequent records may be missing.
+
+In the last case (EOVERFLOW) there may be missing data, in the first two cases
+(EIO, EFAULT) there will be missing data. It's up to the application if it will
+continue reading subsequent data or rather exit.
+
+Open:
+-----
+Only one user is allowed to open the char device. If it is already in use, the
+open function will fail (return a negative value) and set errno to EBUSY.
+The open function may also fail if an IUCV connection to the *MONITOR service
+cannot be established. In this case errno will be set to EIO and an error
+message with an IPUSER SEVER code will be printed into syslog. The IPUSER SEVER
+codes are described in the "z/VM Performance" book, Appendix A.
+
+NOTE:
+-----
+As soon as the device is opened, incoming messages will be accepted and they
+will account for the message limit, i.e. opening the device without reading
+from it will provoke the "message limit reached" error (EOVERFLOW error code)
+eventually.
+
diff --git a/Documentation/s390/s390dbf.txt b/Documentation/s390/s390dbf.txt
new file mode 100644
index 000000000000..2d1cd939b4df
--- /dev/null
+++ b/Documentation/s390/s390dbf.txt
@@ -0,0 +1,615 @@
+S390 Debug Feature
+==================
+
+files: arch/s390/kernel/debug.c
+       include/asm-s390/debug.h
+
+Description:
+------------
+The goal of this feature is to provide a kernel debug logging API 
+where log records can be stored efficiently in memory, where each component 
+(e.g. device drivers) can have one separate debug log.
+One purpose of this is to inspect the debug logs after a production system crash
+in order to analyze the reason for the crash.
+If the system still runs but only a subcomponent which uses dbf failes,
+it is possible to look at the debug logs on a live system via the Linux proc
+filesystem.
+The debug feature may also very useful for kernel and driver development.
+
+Design:
+-------
+Kernel components (e.g. device drivers) can register themselves at the debug 
+feature with the function call debug_register(). This function initializes a 
+debug log for the caller. For each debug log exists a number of debug areas 
+where exactly one is active at one time.  Each debug area consists of contiguous
+pages in memory. In the debug areas there are stored debug entries (log records)
+which are written by event- and exception-calls. 
+
+An event-call writes the specified debug entry to the active debug
+area and updates the log pointer for the active area. If the end 
+of the active debug area is reached, a wrap around is done (ring buffer) 
+and the next debug entry will be written at the beginning of the active 
+debug area.
+
+An exception-call writes the specified debug entry to the log and
+switches to the next debug area. This is done in order to be sure
+that the records which describe the origin of the exception are not
+overwritten when a wrap around for the current area occurs.
+
+The debug areas itselve are also ordered in form of a ring buffer. 
+When an exception is thrown in the last debug area, the following debug 
+entries are then written again in the very first area.
+
+There are three versions for the event- and exception-calls: One for
+logging raw data, one for text and one for numbers.
+
+Each debug entry contains the following data:
+
+- Timestamp
+- Cpu-Number of calling task
+- Level of debug entry (0...6)
+- Return Address to caller
+- Flag, if entry is an exception or not
+
+The debug logs can be inspected in a live system through entries in
+the proc-filesystem. Under the path /proc/s390dbf there is 
+a directory for each registered component, which is named like the
+corresponding component.
+
+The content of the directories are files which represent different views
+to the debug log. Each component can decide which views should be
+used through registering them with the function debug_register_view().
+Predefined views for hex/ascii, sprintf and raw binary data are provided.
+It is also possible to define other views. The content of
+a view can be inspected simply by reading the corresponding proc file.
+
+All debug logs have an an actual debug level (range from 0 to 6).
+The default level is 3. Event and Exception functions have a 'level'
+parameter. Only debug entries with a level that is lower or equal
+than the actual level are written to the log. This means, when
+writing events, high priority log entries should have a low level
+value whereas low priority entries should have a high one.
+The actual debug level can be changed with the help of the proc-filesystem 
+through writing a number string "x" to the 'level' proc file which is
+provided for every debug log. Debugging can be switched off completely
+by using "-" on the 'level' proc file.
+
+Example:
+
+> echo "-" > /proc/s390dbf/dasd/level
+
+It is also possible to deactivate the debug feature globally for every
+debug log. You can change the behavior using  2 sysctl parameters in
+/proc/sys/s390dbf:
+There are currently 2 possible triggers, which stop the  debug feature
+globally. The first possbility is to use the "debug_active" sysctl. If
+set to 1 the debug feature is running. If "debug_active" is set to 0 the
+debug feature is turned off.
+The second trigger which stops the debug feature is an kernel oops.
+That prevents the debug feature from overwriting debug information that
+happened before the oops. After an oops you can reactivate the debug feature
+by piping 1 to /proc/sys/s390dbf/debug_active. Nevertheless, its not
+suggested to use an oopsed kernel in an production environment.
+If you want to disallow the deactivation of the debug feature, you can use
+the "debug_stoppable" sysctl. If you set "debug_stoppable" to 0 the debug
+feature cannot be stopped. If the debug feature is already stopped, it
+will stay deactivated.
+
+Kernel Interfaces:
+------------------
+
+----------------------------------------------------------------------------
+debug_info_t *debug_register(char *name, int pages_index, int nr_areas,
+                             int buf_size);
+
+Parameter:    name:        Name of debug log (e.g. used for proc entry) 
+              pages_index: 2^pages_index pages will be allocated per area
+              nr_areas:    number of debug areas
+              buf_size:    size of data area in each debug entry
+
+Return Value: Handle for generated debug area   
+              NULL if register failed 
+
+Description:  Allocates memory for a debug log     
+              Must not be called within an interrupt handler 
+
+---------------------------------------------------------------------------
+void debug_unregister (debug_info_t * id);
+
+Parameter:     id:   handle for debug log  
+
+Return Value:  none 
+
+Description:   frees memory for a debug log     
+               Must not be called within an interrupt handler 
+
+---------------------------------------------------------------------------
+void debug_set_level (debug_info_t * id, int new_level);
+
+Parameter:     id:        handle for debug log  
+               new_level: new debug level 
+
+Return Value:  none 
+
+Description:   Sets new actual debug level if new_level is valid. 
+
+---------------------------------------------------------------------------
++void debug_stop_all(void);
+
+Parameter:     none
+
+Return Value:  none
+
+Description:   stops the debug feature if stopping is allowed. Currently
+               used in case of a kernel oops.
+
+---------------------------------------------------------------------------
+debug_entry_t* debug_event (debug_info_t* id, int level, void* data, 
+                            int length);
+
+Parameter:     id:     handle for debug log  
+               level:  debug level           
+               data:   pointer to data for debug entry  
+               length: length of data in bytes       
+
+Return Value:  Address of written debug entry 
+
+Description:   writes debug entry to active debug area (if level <= actual 
+               debug level)    
+
+---------------------------------------------------------------------------
+debug_entry_t* debug_int_event (debug_info_t * id, int level, 
+                                unsigned int data);
+debug_entry_t* debug_long_event(debug_info_t * id, int level,
+                                unsigned long data);
+
+Parameter:     id:     handle for debug log  
+               level:  debug level           
+               data:   integer value for debug entry           
+
+Return Value:  Address of written debug entry 
+
+Description:   writes debug entry to active debug area (if level <= actual 
+               debug level)    
+
+---------------------------------------------------------------------------
+debug_entry_t* debug_text_event (debug_info_t * id, int level, 
+                                 const char* data);
+
+Parameter:     id:     handle for debug log  
+               level:  debug level           
+               data:   string for debug entry  
+
+Return Value:  Address of written debug entry 
+
+Description:   writes debug entry in ascii format to active debug area 
+               (if level <= actual debug level)     
+
+---------------------------------------------------------------------------
+debug_entry_t* debug_sprintf_event (debug_info_t * id, int level, 
+                                    char* string,...);
+
+Parameter:     id:    handle for debug log 
+               level: debug level
+               string: format string for debug entry 
+               ...: varargs used as in sprintf()
+
+Return Value:  Address of written debug entry
+
+Description:   writes debug entry with format string and varargs (longs) to 
+               active debug area (if level $<=$ actual debug level). 
+               floats and long long datatypes cannot be used as varargs.
+
+---------------------------------------------------------------------------
+
+debug_entry_t* debug_exception (debug_info_t* id, int level, void* data, 
+                                int length);
+
+Parameter:     id:     handle for debug log  
+               level:  debug level           
+               data:   pointer to data for debug entry  
+               length: length of data in bytes       
+
+Return Value:  Address of written debug entry 
+
+Description:   writes debug entry to active debug area (if level <= actual 
+               debug level) and switches to next debug area  
+
+---------------------------------------------------------------------------
+debug_entry_t* debug_int_exception (debug_info_t * id, int level, 
+                                    unsigned int data);
+debug_entry_t* debug_long_exception(debug_info_t * id, int level,
+                                    unsigned long data);
+
+Parameter:     id:     handle for debug log  
+               level:  debug level           
+               data:   integer value for debug entry           
+
+Return Value:  Address of written debug entry 
+
+Description:   writes debug entry to active debug area (if level <= actual 
+               debug level) and switches to next debug area  
+
+---------------------------------------------------------------------------
+debug_entry_t* debug_text_exception (debug_info_t * id, int level, 
+                                     const char* data);
+
+Parameter:     id:     handle for debug log  
+               level:  debug level           
+               data:   string for debug entry  
+
+Return Value:  Address of written debug entry 
+
+Description:   writes debug entry in ascii format to active debug area 
+               (if level <= actual debug level) and switches to next debug 
+               area  
+
+---------------------------------------------------------------------------
+debug_entry_t* debug_sprintf_exception (debug_info_t * id, int level,
+                                        char* string,...);
+
+Parameter:     id:    handle for debug log  
+               level: debug level  
+               string: format string for debug entry  
+               ...: varargs used as in sprintf()
+
+Return Value:  Address of written debug entry 
+
+Description:   writes debug entry with format string and varargs (longs) to 
+               active debug area (if level $<=$ actual debug level) and
+               switches to next debug area. 
+               floats and long long datatypes cannot be used as varargs.
+
+---------------------------------------------------------------------------
+
+int debug_register_view (debug_info_t * id, struct debug_view *view);
+
+Parameter:     id:    handle for debug log  
+               view:  pointer to debug view struct 
+
+Return Value:  0  : ok 
+               < 0: Error 
+
+Description:   registers new debug view and creates proc dir entry 
+
+---------------------------------------------------------------------------
+int debug_unregister_view (debug_info_t * id, struct debug_view *view); 
+
+Parameter:     id:    handle for debug log  
+               view:  pointer to debug view struct 
+
+Return Value:  0  : ok 
+               < 0: Error 
+
+Description:   unregisters debug view and removes proc dir entry 
+
+
+
+Predefined views:
+-----------------
+
+extern struct debug_view debug_hex_ascii_view;
+extern struct debug_view debug_raw_view;
+extern struct debug_view debug_sprintf_view;
+
+Examples
+--------
+
+/*
+ * hex_ascii- + raw-view Example
+ */
+
+#include <linux/init.h>
+#include <asm/debug.h>
+
+static debug_info_t* debug_info;
+
+static int init(void)
+{
+    /* register 4 debug areas with one page each and 4 byte data field */
+
+    debug_info = debug_register ("test", 0, 4, 4 );
+    debug_register_view(debug_info,&debug_hex_ascii_view);
+    debug_register_view(debug_info,&debug_raw_view);
+
+    debug_text_event(debug_info, 4 , "one ");
+    debug_int_exception(debug_info, 4, 4711);
+    debug_event(debug_info, 3, &debug_info, 4);
+
+    return 0;
+}
+
+static void cleanup(void)
+{
+    debug_unregister (debug_info);
+}
+
+module_init(init);
+module_exit(cleanup);
+
+---------------------------------------------------------------------------
+
+/*
+ * sprintf-view Example
+ */
+
+#include <linux/init.h>
+#include <asm/debug.h>
+
+static debug_info_t* debug_info;
+
+static int init(void)
+{
+    /* register 4 debug areas with one page each and data field for */
+    /* format string pointer + 2 varargs (= 3 * sizeof(long))       */
+
+    debug_info = debug_register ("test", 0, 4, sizeof(long) * 3);
+    debug_register_view(debug_info,&debug_sprintf_view);
+
+    debug_sprintf_event(debug_info, 2 , "first event in %s:%i\n",__FILE__,__LINE__);
+    debug_sprintf_exception(debug_info, 1, "pointer to debug info: %p\n",&debug_info);
+
+    return 0;
+}
+
+static void cleanup(void)
+{
+    debug_unregister (debug_info);
+}
+
+module_init(init);
+module_exit(cleanup);
+
+
+
+ProcFS Interface
+----------------
+Views to the debug logs can be investigated through reading the corresponding 
+proc-files:
+
+Example:
+
+> ls /proc/s390dbf/dasd
+flush  hex_ascii  level      raw 
+> cat /proc/s390dbf/dasd/hex_ascii | sort +1
+00 00974733272:680099 2 - 02 0006ad7e  07 ea 4a 90 | ....
+00 00974733272:682210 2 - 02 0006ade6  46 52 45 45 | FREE
+00 00974733272:682213 2 - 02 0006adf6  07 ea 4a 90 | ....
+00 00974733272:682281 1 * 02 0006ab08  41 4c 4c 43 | EXCP 
+01 00974733272:682284 2 - 02 0006ab16  45 43 4b 44 | ECKD
+01 00974733272:682287 2 - 02 0006ab28  00 00 00 04 | ....
+01 00974733272:682289 2 - 02 0006ab3e  00 00 00 20 | ... 
+01 00974733272:682297 2 - 02 0006ad7e  07 ea 4a 90 | ....
+01 00974733272:684384 2 - 00 0006ade6  46 52 45 45 | FREE
+01 00974733272:684388 2 - 00 0006adf6  07 ea 4a 90 | ....
+
+See section about predefined views for explanation of the above output!
+
+Changing the debug level
+------------------------
+
+Example:
+
+
+> cat /proc/s390dbf/dasd/level
+3
+> echo "5" > /proc/s390dbf/dasd/level
+> cat /proc/s390dbf/dasd/level
+5
+
+Flushing debug areas
+--------------------
+Debug areas can be flushed with piping the number of the desired
+area (0...n) to the proc file "flush". When using "-" all debug areas
+are flushed.
+
+Examples:
+
+1. Flush debug area 0:
+> echo "0" > /proc/s390dbf/dasd/flush  
+
+2. Flush all debug areas:
+> echo "-" > /proc/s390dbf/dasd/flush
+
+Stooping the debug feature
+--------------------------
+Example:
+
+1. Check if stopping is allowed
+> cat /proc/sys/s390dbf/debug_stoppable
+2. Stop debug feature
+> echo 0 > /proc/sys/s390dbf/debug_active
+
+lcrash Interface
+----------------
+It is planned that the dump analysis tool lcrash gets an additional command
+'s390dbf' to display all the debug logs. With this tool it will be possible 
+to investigate the debug logs on a live system and with a memory dump after 
+a system crash.
+
+Investigating raw memory
+------------------------
+One last possibility to investigate the debug logs at a live
+system and after a system crash is to look at the raw memory
+under VM or at the Service Element.
+It is possible to find the anker of the debug-logs through
+the 'debug_area_first' symbol in the System map. Then one has
+to follow the correct pointers of the data-structures defined
+in debug.h and find the debug-areas in memory.
+Normally modules which use the debug feature will also have
+a global variable with the pointer to the debug-logs. Following
+this pointer it will also be possible to find the debug logs in
+memory.
+
+For this method it is recommended to use '16 * x + 4' byte (x = 0..n)
+for the length of the data field in debug_register() in
+order to see the debug entries well formatted.
+
+
+Predefined Views
+----------------
+
+There are three predefined views: hex_ascii, raw and sprintf. 
+The hex_ascii view shows the data field in hex and ascii representation 
+(e.g. '45 43 4b 44 | ECKD'). 
+The raw view returns a bytestream as the debug areas are stored in memory.
+
+The sprintf view formats the debug entries in the same way as the sprintf
+function would do. The sprintf event/expection fuctions write to the 
+debug entry a pointer to the format string (size = sizeof(long)) 
+and for each vararg a long value. So e.g. for a debug entry with a format 
+string plus two varargs one would need to allocate a (3 * sizeof(long)) 
+byte data area in the debug_register() function.
+
+
+NOTE: If using the sprintf view do NOT use other event/exception functions
+than the sprintf-event and -exception functions.
+
+The format of the hex_ascii and sprintf view is as follows:
+- Number of area
+- Timestamp (formatted as seconds and microseconds since 00:00:00 Coordinated 
+  Universal Time (UTC), January 1, 1970)
+- level of debug entry
+- Exception flag (* = Exception)
+- Cpu-Number of calling task
+- Return Address to caller
+- data field
+
+The format of the raw view is:
+- Header as described in debug.h
+- datafield 
+
+A typical line of the hex_ascii view will look like the following (first line 
+is only for explanation and will not be displayed when 'cating' the view):
+
+area  time           level exception cpu caller    data (hex + ascii)
+--------------------------------------------------------------------------
+00    00964419409:440690 1 -         00  88023fe   
+
+
+Defining views
+--------------
+
+Views are specified with the 'debug_view' structure. There are defined
+callback functions which are used for reading and writing the proc files:
+
+struct debug_view {
+        char name[DEBUG_MAX_PROCF_LEN];  
+        debug_prolog_proc_t* prolog_proc; 
+        debug_header_proc_t* header_proc;
+        debug_format_proc_t* format_proc;
+        debug_input_proc_t*  input_proc;
+	void*                private_data;
+};
+
+where
+
+typedef int (debug_header_proc_t) (debug_info_t* id,
+                                   struct debug_view* view,
+                                   int area,
+                                   debug_entry_t* entry,
+                                   char* out_buf);
+
+typedef int (debug_format_proc_t) (debug_info_t* id,
+                                   struct debug_view* view, char* out_buf,
+                                   const char* in_buf);
+typedef int (debug_prolog_proc_t) (debug_info_t* id,
+                                   struct debug_view* view,
+                                   char* out_buf);
+typedef int (debug_input_proc_t) (debug_info_t* id,
+                                  struct debug_view* view,
+                                  struct file* file, const char* user_buf,
+                                  size_t in_buf_size, loff_t* offset);
+
+
+The "private_data" member can be used as pointer to view specific data.
+It is not used by the debug feature itself.
+
+The output when reading a debug-proc file is structured like this:
+
+"prolog_proc output"
+
+"header_proc output 1"  "format_proc output 1"
+"header_proc output 2"  "format_proc output 2"
+"header_proc output 3"  "format_proc output 3"
+...
+
+When a view is read from the proc fs, the Debug Feature calls the 
+'prolog_proc' once for writing the prolog.
+Then 'header_proc' and 'format_proc' are called for each 
+existing debug entry.
+
+The input_proc can be used to implement functionality when it is written to 
+the view (e.g. like with 'echo "0" > /proc/s390dbf/dasd/level).
+
+For header_proc there can be used the default function
+debug_dflt_header_fn() which is defined in in debug.h.
+and which produces the same header output as the predefined views.
+E.g:
+00 00964419409:440761 2 - 00 88023ec
+
+In order to see how to use the callback functions check the implementation
+of the default views!
+
+Example
+
+#include <asm/debug.h>
+
+#define UNKNOWNSTR "data: %08x"
+
+const char* messages[] =
+{"This error...........\n",
+ "That error...........\n",
+ "Problem..............\n",
+ "Something went wrong.\n",
+ "Everything ok........\n",
+ NULL
+};
+
+static int debug_test_format_fn(
+   debug_info_t * id, struct debug_view *view, 
+   char *out_buf, const char *in_buf
+)
+{
+  int i, rc = 0;
+
+  if(id->buf_size >= 4) {
+     int msg_nr = *((int*)in_buf);
+     if(msg_nr < sizeof(messages)/sizeof(char*) - 1)
+        rc += sprintf(out_buf, "%s", messages[msg_nr]);	
+     else
+        rc += sprintf(out_buf, UNKNOWNSTR, msg_nr);
+  }
+ out:
+   return rc;
+}
+
+struct debug_view debug_test_view = {
+  "myview",                 /* name of view */
+  NULL,                     /* no prolog */
+  &debug_dflt_header_fn,    /* default header for each entry */
+  &debug_test_format_fn,    /* our own format function */
+  NULL,                     /* no input function */
+  NULL                      /* no private data */
+};
+
+=====
+test:
+=====
+debug_info_t *debug_info;
+...
+debug_info = debug_register ("test", 0, 4, 4 ));
+debug_register_view(debug_info, &debug_test_view);
+for(i = 0; i < 10; i ++) debug_int_event(debug_info, 1, i);
+
+> cat /proc/s390dbf/test/myview
+00 00964419734:611402 1 - 00 88042ca   This error...........
+00 00964419734:611405 1 - 00 88042ca   That error...........
+00 00964419734:611408 1 - 00 88042ca   Problem..............
+00 00964419734:611411 1 - 00 88042ca   Something went wrong.
+00 00964419734:611414 1 - 00 88042ca   Everything ok........
+00 00964419734:611417 1 - 00 88042ca   data: 00000005
+00 00964419734:611419 1 - 00 88042ca   data: 00000006
+00 00964419734:611422 1 - 00 88042ca   data: 00000007
+00 00964419734:611425 1 - 00 88042ca   data: 00000008
+00 00964419734:611428 1 - 00 88042ca   data: 00000009