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!

1 files changed, 979 insertions, 0 deletions

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="Linux-USB-API">
+ <bookinfo>
+  <title>The Linux-USB Host Side API</title>
+  
+  <legalnotice>
+   <para>
+     This documentation is free software; you can redistribute
+     it and/or modify it under the terms of the GNU General Public
+     License as published by the Free Software Foundation; either
+     version 2 of the License, or (at your option) any later
+     version.
+   </para>
+      
+   <para>
+     This program is distributed in the hope that it will be
+     useful, but WITHOUT ANY WARRANTY; without even the implied
+     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+     See the GNU General Public License for more details.
+   </para>
+      
+   <para>
+     You should have received a copy of the GNU General Public
+     License along with this program; if not, write to the Free
+     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+     MA 02111-1307 USA
+   </para>
+      
+   <para>
+     For more details see the file COPYING in the source
+     distribution of Linux.
+   </para>
+  </legalnotice>
+ </bookinfo>
+
+<toc></toc>
+
+<chapter id="intro">
+    <title>Introduction to USB on Linux</title>
+
+    <para>A Universal Serial Bus (USB) is used to connect a host,
+    such as a PC or workstation, to a number of peripheral
+    devices.  USB uses a tree structure, with the host at the
+    root (the system's master), hubs as interior nodes, and
+    peripheral devices as leaves (and slaves).
+    Modern PCs support several such trees of USB devices, usually
+    one USB 2.0 tree (480 Mbit/sec each) with
+    a few USB 1.1 trees (12 Mbit/sec each) that are used when you
+    connect a USB 1.1 device directly to the machine's "root hub".
+    </para>
+
+    <para>That master/slave asymmetry was designed in part for
+    ease of use.  It is not physically possible to assemble
+    (legal) USB cables incorrectly:  all upstream "to-the-host"
+    connectors are the rectangular type, matching the sockets on
+    root hubs, and the downstream type are the squarish type
+    (or they are built in to the peripheral).
+    Software doesn't need to deal with distributed autoconfiguration
+    since the pre-designated master node manages all that.
+    At the electrical level, bus protocol overhead is reduced by
+    eliminating arbitration and moving scheduling into host software.
+    </para>
+
+    <para>USB 1.0 was announced in January 1996, and was revised
+    as USB 1.1 (with improvements in hub specification and
+    support for interrupt-out transfers) in September 1998.
+    USB 2.0 was released in April 2000, including high speed
+    transfers and transaction translating hubs (used for USB 1.1
+    and 1.0 backward compatibility).
+    </para>
+
+    <para>USB support was added to Linux early in the 2.2 kernel series
+    shortly before the 2.3 development forked off.  Updates
+    from 2.3 were regularly folded back into 2.2 releases, bringing
+    new features such as <filename>/sbin/hotplug</filename> support,
+    more drivers, and more robustness.
+    The 2.5 kernel series continued such improvements, and also
+    worked on USB 2.0 support,
+    higher performance,
+    better consistency between host controller drivers,
+    API simplification (to make bugs less likely),
+    and providing internal "kerneldoc" documentation.
+    </para>
+
+    <para>Linux can run inside USB devices as well as on
+    the hosts that control the devices.
+    Because the Linux 2.x USB support evolved to support mass market
+    platforms such as Apple Macintosh or PC-compatible systems,
+    it didn't address design concerns for those types of USB systems.
+    So it can't be used inside mass-market PDAs, or other peripherals.
+    USB device drivers running inside those Linux peripherals
+    don't do the same things as the ones running inside hosts,
+    and so they've been given a different name:
+    they're called <emphasis>gadget drivers</emphasis>.
+    This document does not present gadget drivers.
+    </para>
+
+    </chapter>
+
+<chapter id="host">
+    <title>USB Host-Side API Model</title>
+
+    <para>Within the kernel,
+    host-side drivers for USB devices talk to the "usbcore" APIs.
+    There are two types of public "usbcore" APIs, targetted at two different
+    layers of USB driver.  Those are
+    <emphasis>general purpose</emphasis> drivers, exposed through
+    driver frameworks such as block, character, or network devices;
+    and drivers that are <emphasis>part of the core</emphasis>,
+    which are involved in managing a USB bus.
+    Such core drivers include the <emphasis>hub</emphasis> driver,
+    which manages trees of USB devices, and several different kinds
+    of <emphasis>host controller driver (HCD)</emphasis>,
+    which control individual busses.
+    </para>
+
+    <para>The device model seen by USB drivers is relatively complex.
+    </para>
+     
+    <itemizedlist>
+
+	<listitem><para>USB supports four kinds of data transfer
+	(control, bulk, interrupt, and isochronous).  Two transfer
+	types use bandwidth as it's available (control and bulk),
+	while the other two types of transfer (interrupt and isochronous)
+	are scheduled to provide guaranteed bandwidth.
+	</para></listitem>
+
+	<listitem><para>The device description model includes one or more
+	"configurations" per device, only one of which is active at a time.
+	Devices that are capable of high speed operation must also support
+	full speed configurations, along with a way to ask about the
+	"other speed" configurations that might be used.
+	</para></listitem>
+
+	<listitem><para>Configurations have one or more "interface", each
+	of which may have "alternate settings".  Interfaces may be
+	standardized by USB "Class" specifications, or may be specific to
+	a vendor or device.</para>
+
+	<para>USB device drivers actually bind to interfaces, not devices.
+	Think of them as "interface drivers", though you
+	may not see many devices where the distinction is important.
+	<emphasis>Most USB devices are simple, with only one configuration,
+	one interface, and one alternate setting.</emphasis>
+	</para></listitem>
+
+	<listitem><para>Interfaces have one or more "endpoints", each of
+	which supports one type and direction of data transfer such as
+	"bulk out" or "interrupt in".  The entire configuration may have
+	up to sixteen endpoints in each direction, allocated as needed
+	among all the interfaces.
+	</para></listitem>
+
+	<listitem><para>Data transfer on USB is packetized; each endpoint
+	has a maximum packet size.
+	Drivers must often be aware of conventions such as flagging the end
+	of bulk transfers using "short" (including zero length) packets.
+	</para></listitem>
+
+	<listitem><para>The Linux USB API supports synchronous calls for
+	control and bulk messaging.
+	It also supports asynchnous calls for all kinds of data transfer,
+	using request structures called "URBs" (USB Request Blocks).
+	</para></listitem>
+
+    </itemizedlist>
+
+    <para>Accordingly, the USB Core API exposed to device drivers
+    covers quite a lot of territory.  You'll probably need to consult
+    the USB 2.0 specification, available online from www.usb.org at
+    no cost, as well as class or device specifications.
+    </para>
+
+    <para>The only host-side drivers that actually touch hardware
+    (reading/writing registers, handling IRQs, and so on) are the HCDs.
+    In theory, all HCDs provide the same functionality through the same
+    API.  In practice, that's becoming more true on the 2.5 kernels,
+    but there are still differences that crop up especially with
+    fault handling.  Different controllers don't necessarily report
+    the same aspects of failures, and recovery from faults (including
+    software-induced ones like unlinking an URB) isn't yet fully
+    consistent.
+    Device driver authors should make a point of doing disconnect
+    testing (while the device is active) with each different host
+    controller driver, to make sure drivers don't have bugs of
+    their own as well as to make sure they aren't relying on some
+    HCD-specific behavior.
+    (You will need external USB 1.1 and/or
+    USB 2.0 hubs to perform all those tests.)
+    </para>
+
+    </chapter>
+
+<chapter><title>USB-Standard Types</title>
+
+    <para>In <filename>&lt;linux/usb_ch9.h&gt;</filename> you will find
+    the USB data types defined in chapter 9 of the USB specification.
+    These data types are used throughout USB, and in APIs including
+    this host side API, gadget APIs, and usbfs.
+    </para>
+
+!Iinclude/linux/usb_ch9.h
+
+    </chapter>
+
+<chapter><title>Host-Side Data Types and Macros</title>
+
+    <para>The host side API exposes several layers to drivers, some of
+    which are more necessary than others.
+    These support lifecycle models for host side drivers
+    and devices, and support passing buffers through usbcore to
+    some HCD that performs the I/O for the device driver.
+    </para>
+
+
+!Iinclude/linux/usb.h
+
+    </chapter>
+
+    <chapter><title>USB Core APIs</title>
+
+    <para>There are two basic I/O models in the USB API.
+    The most elemental one is asynchronous:  drivers submit requests
+    in the form of an URB, and the URB's completion callback
+    handle the next step.
+    All USB transfer types support that model, although there
+    are special cases for control URBs (which always have setup
+    and status stages, but may not have a data stage) and
+    isochronous URBs (which allow large packets and include
+    per-packet fault reports).
+    Built on top of that is synchronous API support, where a
+    driver calls a routine that allocates one or more URBs,
+    submits them, and waits until they complete.
+    There are synchronous wrappers for single-buffer control
+    and bulk transfers (which are awkward to use in some
+    driver disconnect scenarios), and for scatterlist based
+    streaming i/o (bulk or interrupt).
+    </para>
+
+    <para>USB drivers need to provide buffers that can be
+    used for DMA, although they don't necessarily need to
+    provide the DMA mapping themselves.
+    There are APIs to use used when allocating DMA buffers,
+    which can prevent use of bounce buffers on some systems.
+    In some cases, drivers may be able to rely on 64bit DMA
+    to eliminate another kind of bounce buffer.
+    </para>
+
+!Edrivers/usb/core/urb.c
+!Edrivers/usb/core/message.c
+!Edrivers/usb/core/file.c
+!Edrivers/usb/core/usb.c
+!Edrivers/usb/core/hub.c
+    </chapter>
+
+    <chapter><title>Host Controller APIs</title>
+
+    <para>These APIs are only for use by host controller drivers,
+    most of which implement standard register interfaces such as
+    EHCI, OHCI, or UHCI.
+    UHCI was one of the first interfaces, designed by Intel and
+    also used by VIA; it doesn't do much in hardware.
+    OHCI was designed later, to have the hardware do more work
+    (bigger transfers, tracking protocol state, and so on).
+    EHCI was designed with USB 2.0; its design has features that
+    resemble OHCI (hardware does much more work) as well as
+    UHCI (some parts of ISO support, TD list processing).
+    </para>
+
+    <para>There are host controllers other than the "big three",
+    although most PCI based controllers (and a few non-PCI based
+    ones) use one of those interfaces.
+    Not all host controllers use DMA; some use PIO, and there
+    is also a simulator.
+    </para>
+
+    <para>The same basic APIs are available to drivers for all
+    those controllers.  
+    For historical reasons they are in two layers:
+    <structname>struct usb_bus</structname> is a rather thin
+    layer that became available in the 2.2 kernels, while
+    <structname>struct usb_hcd</structname> is a more featureful
+    layer (available in later 2.4 kernels and in 2.5) that
+    lets HCDs share common code, to shrink driver size
+    and significantly reduce hcd-specific behaviors.
+    </para>
+
+!Edrivers/usb/core/hcd.c
+!Edrivers/usb/core/hcd-pci.c
+!Edrivers/usb/core/buffer.c
+    </chapter>
+
+    <chapter>
+	<title>The USB Filesystem (usbfs)</title>
+
+	<para>This chapter presents the Linux <emphasis>usbfs</emphasis>.
+	You may prefer to avoid writing new kernel code for your
+	USB driver; that's the problem that usbfs set out to solve.
+	User mode device drivers are usually packaged as applications
+	or libraries, and may use usbfs through some programming library
+	that wraps it.  Such libraries include
+	<ulink url="http://libusb.sourceforge.net">libusb</ulink>
+	for C/C++, and
+	<ulink url="http://jUSB.sourceforge.net">jUSB</ulink> for Java.
+	</para>
+
+	<note><title>Unfinished</title>
+	    <para>This particular documentation is incomplete,
+	    especially with respect to the asynchronous mode.
+	    As of kernel 2.5.66 the code and this (new) documentation
+	    need to be cross-reviewed.
+	    </para>
+	    </note>
+
+	<para>Configure usbfs into Linux kernels by enabling the
+	<emphasis>USB filesystem</emphasis> option (CONFIG_USB_DEVICEFS),
+	and you get basic support for user mode USB device drivers.
+	Until relatively recently it was often (confusingly) called
+	<emphasis>usbdevfs</emphasis> although it wasn't solving what
+	<emphasis>devfs</emphasis> was.
+	Every USB device will appear in usbfs, regardless of whether or
+	not it has a kernel driver; but only devices with kernel drivers
+	show up in devfs.
+	</para>
+
+	<sect1>
+	    <title>What files are in "usbfs"?</title>
+
+	    <para>Conventionally mounted at
+	    <filename>/proc/bus/usb</filename>, usbfs 
+	    features include:
+	    <itemizedlist>
+		<listitem><para><filename>/proc/bus/usb/devices</filename>
+		    ... a text file
+		    showing each of the USB devices on known to the kernel,
+		    and their configuration descriptors.
+		    You can also poll() this to learn about new devices.
+		    </para></listitem>
+		<listitem><para><filename>/proc/bus/usb/BBB/DDD</filename>
+		    ... magic files
+		    exposing the each device's configuration descriptors, and
+		    supporting a series of ioctls for making device requests,
+		    including I/O to devices.  (Purely for access by programs.)
+		    </para></listitem>
+	    </itemizedlist>
+	    </para>
+
+	    <para> Each bus is given a number (BBB) based on when it was
+	    enumerated; within each bus, each device is given a similar
+	    number (DDD).
+	    Those BBB/DDD paths are not "stable" identifiers;
+	    expect them to change even if you always leave the devices
+	    plugged in to the same hub port.
+	    <emphasis>Don't even think of saving these in application
+	    configuration files.</emphasis>
+	    Stable identifiers are available, for user mode applications
+	    that want to use them.  HID and networking devices expose
+	    these stable IDs, so that for example you can be sure that
+	    you told the right UPS to power down its second server.
+	    "usbfs" doesn't (yet) expose those IDs.
+	    </para>
+
+	</sect1>
+
+	<sect1>
+	    <title>Mounting and Access Control</title>
+
+	    <para>There are a number of mount options for usbfs, which will
+	    be of most interest to you if you need to override the default
+	    access control policy.
+	    That policy is that only root may read or write device files
+	    (<filename>/proc/bus/BBB/DDD</filename>) although anyone may read
+	    the <filename>devices</filename>
+	    or <filename>drivers</filename> files.
+	    I/O requests to the device also need the CAP_SYS_RAWIO capability,
+	    </para>
+
+	    <para>The significance of that is that by default, all user mode
+	    device drivers need super-user privileges.
+	    You can change modes or ownership in a driver setup
+	    when the device hotplugs, or maye just start the
+	    driver right then, as a privileged server (or some activity
+	    within one).
+	    That's the most secure approach for multi-user systems,
+	    but for single user systems ("trusted" by that user)
+	    it's more convenient just to grant everyone all access
+	    (using the <emphasis>devmode=0666</emphasis> option)
+	    so the driver can start whenever it's needed.
+	    </para>
+
+	    <para>The mount options for usbfs, usable in /etc/fstab or
+	    in command line invocations of <emphasis>mount</emphasis>, are:
+
+	    <variablelist>
+		<varlistentry>
+		    <term><emphasis>busgid</emphasis>=NNNNN</term>
+		    <listitem><para>Controls the GID used for the
+		    /proc/bus/usb/BBB
+		    directories.  (Default: 0)</para></listitem></varlistentry>
+		<varlistentry><term><emphasis>busmode</emphasis>=MMM</term>
+		    <listitem><para>Controls the file mode used for the
+		    /proc/bus/usb/BBB
+		    directories.  (Default: 0555)
+		    </para></listitem></varlistentry>
+		<varlistentry><term><emphasis>busuid</emphasis>=NNNNN</term>
+		    <listitem><para>Controls the UID used for the
+		    /proc/bus/usb/BBB
+		    directories.  (Default: 0)</para></listitem></varlistentry>
+
+		<varlistentry><term><emphasis>devgid</emphasis>=NNNNN</term>
+		    <listitem><para>Controls the GID used for the
+		    /proc/bus/usb/BBB/DDD
+		    files.  (Default: 0)</para></listitem></varlistentry>
+		<varlistentry><term><emphasis>devmode</emphasis>=MMM</term>
+		    <listitem><para>Controls the file mode used for the
+		    /proc/bus/usb/BBB/DDD
+		    files.  (Default: 0644)</para></listitem></varlistentry>
+		<varlistentry><term><emphasis>devuid</emphasis>=NNNNN</term>
+		    <listitem><para>Controls the UID used for the
+		    /proc/bus/usb/BBB/DDD
+		    files.  (Default: 0)</para></listitem></varlistentry>
+
+		<varlistentry><term><emphasis>listgid</emphasis>=NNNNN</term>
+		    <listitem><para>Controls the GID used for the
+		    /proc/bus/usb/devices and drivers files.
+		    (Default: 0)</para></listitem></varlistentry>
+		<varlistentry><term><emphasis>listmode</emphasis>=MMM</term>
+		    <listitem><para>Controls the file mode used for the
+		    /proc/bus/usb/devices and drivers files.
+		    (Default: 0444)</para></listitem></varlistentry>
+		<varlistentry><term><emphasis>listuid</emphasis>=NNNNN</term>
+		    <listitem><para>Controls the UID used for the
+		    /proc/bus/usb/devices and drivers files.
+		    (Default: 0)</para></listitem></varlistentry>
+	    </variablelist>
+
+	    </para>
+
+	    <para>Note that many Linux distributions hard-wire the mount options
+	    for usbfs in their init scripts, such as
+	    <filename>/etc/rc.d/rc.sysinit</filename>,
+	    rather than making it easy to set this per-system
+	    policy in <filename>/etc/fstab</filename>.
+	    </para>
+
+	</sect1>
+
+	<sect1>
+	    <title>/proc/bus/usb/devices</title>
+
+	    <para>This file is handy for status viewing tools in user
+	    mode, which can scan the text format and ignore most of it.
+	    More detailed device status (including class and vendor
+	    status) is available from device-specific files.
+	    For information about the current format of this file,
+	    see the
+	    <filename>Documentation/usb/proc_usb_info.txt</filename>
+	    file in your Linux kernel sources.
+	    </para>
+
+	    <para>Otherwise the main use for this file from programs
+	    is to poll() it to get notifications of usb devices
+	    as they're plugged or unplugged.
+	    To see what changed, you'd need to read the file and
+	    compare "before" and "after" contents, scan the filesystem,
+	    or see its hotplug event.
+	    </para>
+
+	</sect1>
+
+	<sect1>
+	    <title>/proc/bus/usb/BBB/DDD</title>
+
+	    <para>Use these files in one of these basic ways:
+	    </para>
+
+	    <para><emphasis>They can be read,</emphasis>
+	    producing first the device descriptor
+	    (18 bytes) and then the descriptors for the current configuration.
+	    See the USB 2.0 spec for details about those binary data formats.
+	    You'll need to convert most multibyte values from little endian
+	    format to your native host byte order, although a few of the
+	    fields in the device descriptor (both of the BCD-encoded fields,
+	    and the vendor and product IDs) will be byteswapped for you.
+	    Note that configuration descriptors include descriptors for
+	    interfaces, altsettings, endpoints, and maybe additional
+	    class descriptors.
+	    </para>
+
+	    <para><emphasis>Perform USB operations</emphasis> using 
+	    <emphasis>ioctl()</emphasis> requests to make endpoint I/O
+	    requests (synchronously or asynchronously) or manage
+	    the device.
+	    These requests need the CAP_SYS_RAWIO capability,
+	    as well as filesystem access permissions.
+	    Only one ioctl request can be made on one of these
+	    device files at a time.
+	    This means that if you are synchronously reading an endpoint
+	    from one thread, you won't be able to write to a different
+	    endpoint from another thread until the read completes.
+	    This works for <emphasis>half duplex</emphasis> protocols,
+	    but otherwise you'd use asynchronous i/o requests. 
+	    </para>
+
+	    </sect1>
+
+
+	<sect1>
+	    <title>Life Cycle of User Mode Drivers</title>
+
+	    <para>Such a driver first needs to find a device file
+	    for a device it knows how to handle.
+	    Maybe it was told about it because a
+	    <filename>/sbin/hotplug</filename> event handling agent
+	    chose that driver to handle the new device.
+	    Or maybe it's an application that scans all the
+	    /proc/bus/usb device files, and ignores most devices.
+	    In either case, it should <function>read()</function> all
+	    the descriptors from the device file,
+	    and check them against what it knows how to handle.
+	    It might just reject everything except a particular
+	    vendor and product ID, or need a more complex policy.
+	    </para>
+
+	    <para>Never assume there will only be one such device
+	    on the system at a time!
+	    If your code can't handle more than one device at
+	    a time, at least detect when there's more than one, and
+	    have your users choose which device to use.
+	    </para>
+
+	    <para>Once your user mode driver knows what device to use,
+	    it interacts with it in either of two styles.
+	    The simple style is to make only control requests; some
+	    devices don't need more complex interactions than those.
+	    (An example might be software using vendor-specific control
+	    requests for some initialization or configuration tasks,
+	    with a kernel driver for the rest.)
+	    </para>
+
+	    <para>More likely, you need a more complex style driver:
+	    one using non-control endpoints, reading or writing data
+	    and claiming exclusive use of an interface.
+	    <emphasis>Bulk</emphasis> transfers are easiest to use,
+	    but only their sibling <emphasis>interrupt</emphasis> transfers 
+	    work with low speed devices.
+	    Both interrupt and <emphasis>isochronous</emphasis> transfers
+	    offer service guarantees because their bandwidth is reserved.
+	    Such "periodic" transfers are awkward to use through usbfs,
+	    unless you're using the asynchronous calls.  However, interrupt
+	    transfers can also be used in a synchronous "one shot" style.
+	    </para>
+
+	    <para>Your user-mode driver should never need to worry
+	    about cleaning up request state when the device is
+	    disconnected, although it should close its open file
+	    descriptors as soon as it starts seeing the ENODEV
+	    errors.
+	    </para>
+
+	    </sect1>
+
+	<sect1><title>The ioctl() Requests</title>
+
+	    <para>To use these ioctls, you need to include the following
+	    headers in your userspace program:
+<programlisting>#include &lt;linux/usb.h&gt;
+#include &lt;linux/usbdevice_fs.h&gt;
+#include &lt;asm/byteorder.h&gt;</programlisting>
+	    The standard USB device model requests, from "Chapter 9" of
+	    the USB 2.0 specification, are automatically included from
+	    the <filename>&lt;linux/usb_ch9.h&gt;</filename> header.
+	    </para>
+
+	    <para>Unless noted otherwise, the ioctl requests
+	    described here will
+	    update the modification time on the usbfs file to which
+	    they are applied (unless they fail).
+	    A return of zero indicates success; otherwise, a
+	    standard USB error code is returned.  (These are
+	    documented in
+	    <filename>Documentation/usb/error-codes.txt</filename>
+	    in your kernel sources.)
+	    </para>
+
+	    <para>Each of these files multiplexes access to several
+	    I/O streams, one per endpoint.
+	    Each device has one control endpoint (endpoint zero)
+	    which supports a limited RPC style RPC access.
+	    Devices are configured
+	    by khubd (in the kernel) setting a device-wide
+	    <emphasis>configuration</emphasis> that affects things
+	    like power consumption and basic functionality.
+	    The endpoints are part of USB <emphasis>interfaces</emphasis>,
+	    which may have <emphasis>altsettings</emphasis>
+	    affecting things like which endpoints are available.
+	    Many devices only have a single configuration and interface,
+	    so drivers for them will ignore configurations and altsettings.
+	    </para>
+
+
+	    <sect2>
+		<title>Management/Status Requests</title>
+
+		<para>A number of usbfs requests don't deal very directly
+		with device I/O.
+		They mostly relate to device management and status.
+		These are all synchronous requests.
+		</para>
+
+		<variablelist>
+
+		<varlistentry><term>USBDEVFS_CLAIMINTERFACE</term>
+		    <listitem><para>This is used to force usbfs to
+		    claim a specific interface,
+		    which has not previously been claimed by usbfs or any other
+		    kernel driver.
+		    The ioctl parameter is an integer holding the number of
+		    the interface (bInterfaceNumber from descriptor).
+		    </para><para>
+		    Note that if your driver doesn't claim an interface
+		    before trying to use one of its endpoints, and no
+		    other driver has bound to it, then the interface is
+		    automatically claimed by usbfs.
+		    </para><para>
+		    This claim will be released by a RELEASEINTERFACE ioctl,
+		    or by closing the file descriptor.
+		    File modification time is not updated by this request.
+		    </para></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_CONNECTINFO</term>
+		    <listitem><para>Says whether the device is lowspeed.
+		    The ioctl parameter points to a structure like this:
+<programlisting>struct usbdevfs_connectinfo {
+        unsigned int   devnum;
+        unsigned char  slow;
+}; </programlisting>
+		    File modification time is not updated by this request.
+		    </para><para>
+		    <emphasis>You can't tell whether a "not slow"
+		    device is connected at high speed (480 MBit/sec)
+		    or just full speed (12 MBit/sec).</emphasis>
+		    You should know the devnum value already,
+		    it's the DDD value of the device file name.
+		    </para></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_GETDRIVER</term>
+		    <listitem><para>Returns the name of the kernel driver
+		    bound to a given interface (a string).  Parameter
+		    is a pointer to this structure, which is modified:
+<programlisting>struct usbdevfs_getdriver {
+        unsigned int  interface;
+        char          driver[USBDEVFS_MAXDRIVERNAME + 1];
+};</programlisting>
+		    File modification time is not updated by this request.
+		    </para></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_IOCTL</term>
+		    <listitem><para>Passes a request from userspace through
+		    to a kernel driver that has an ioctl entry in the
+		    <emphasis>struct usb_driver</emphasis> it registered.
+<programlisting>struct usbdevfs_ioctl {
+        int     ifno;
+        int     ioctl_code;
+        void    *data;
+};
+
+/* user mode call looks like this.
+ * 'request' becomes the driver->ioctl() 'code' parameter.
+ * the size of 'param' is encoded in 'request', and that data
+ * is copied to or from the driver->ioctl() 'buf' parameter.
+ */
+static int
+usbdev_ioctl (int fd, int ifno, unsigned request, void *param)
+{
+        struct usbdevfs_ioctl	wrapper;
+
+        wrapper.ifno = ifno;
+        wrapper.ioctl_code = request;
+        wrapper.data = param;
+
+        return ioctl (fd, USBDEVFS_IOCTL, &amp;wrapper);
+} </programlisting>
+		    File modification time is not updated by this request.
+		    </para><para>
+		    This request lets kernel drivers talk to user mode code
+		    through filesystem operations even when they don't create
+		    a charactor or block special device.
+		    It's also been used to do things like ask devices what
+		    device special file should be used.
+		    Two pre-defined ioctls are used
+		    to disconnect and reconnect kernel drivers, so
+		    that user mode code can completely manage binding
+		    and configuration of devices.
+		    </para></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_RELEASEINTERFACE</term>
+		    <listitem><para>This is used to release the claim usbfs
+		    made on interface, either implicitly or because of a
+		    USBDEVFS_CLAIMINTERFACE call, before the file
+		    descriptor is closed.
+		    The ioctl parameter is an integer holding the number of
+		    the interface (bInterfaceNumber from descriptor);
+		    File modification time is not updated by this request.
+		    </para><warning><para>
+		    <emphasis>No security check is made to ensure
+		    that the task which made the claim is the one
+		    which is releasing it.
+		    This means that user mode driver may interfere
+		    other ones.  </emphasis>
+		    </para></warning></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_RESETEP</term>
+		    <listitem><para>Resets the data toggle value for an endpoint
+		    (bulk or interrupt) to DATA0.
+		    The ioctl parameter is an integer endpoint number
+		    (1 to 15, as identified in the endpoint descriptor),
+		    with USB_DIR_IN added if the device's endpoint sends
+		    data to the host.
+		    </para><warning><para>
+		    <emphasis>Avoid using this request.
+		    It should probably be removed.</emphasis>
+		    Using it typically means the device and driver will lose
+		    toggle synchronization.  If you really lost synchronization,
+		    you likely need to completely handshake with the device,
+		    using a request like CLEAR_HALT
+		    or SET_INTERFACE.
+		    </para></warning></listitem></varlistentry>
+
+		</variablelist>
+
+		</sect2>
+
+	    <sect2>
+		<title>Synchronous I/O Support</title>
+
+		<para>Synchronous requests involve the kernel blocking
+		until until the user mode request completes, either by
+		finishing successfully or by reporting an error.
+		In most cases this is the simplest way to use usbfs,
+		although as noted above it does prevent performing I/O
+		to more than one endpoint at a time.
+		</para>
+
+		<variablelist>
+
+		<varlistentry><term>USBDEVFS_BULK</term>
+		    <listitem><para>Issues a bulk read or write request to the
+		    device.
+		    The ioctl parameter is a pointer to this structure:
+<programlisting>struct usbdevfs_bulktransfer {
+        unsigned int  ep;
+        unsigned int  len;
+        unsigned int  timeout; /* in milliseconds */
+        void          *data;
+};</programlisting>
+		    </para><para>The "ep" value identifies a
+		    bulk endpoint number (1 to 15, as identified in an endpoint
+		    descriptor),
+		    masked with USB_DIR_IN when referring to an endpoint which
+		    sends data to the host from the device.
+		    The length of the data buffer is identified by "len";
+		    Recent kernels support requests up to about 128KBytes.
+		    <emphasis>FIXME say how read length is returned,
+		    and how short reads are handled.</emphasis>.
+		    </para></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_CLEAR_HALT</term>
+		    <listitem><para>Clears endpoint halt (stall) and
+		    resets the endpoint toggle.  This is only
+		    meaningful for bulk or interrupt endpoints.
+		    The ioctl parameter is an integer endpoint number
+		    (1 to 15, as identified in an endpoint descriptor),
+		    masked with USB_DIR_IN when referring to an endpoint which
+		    sends data to the host from the device.
+		    </para><para>
+		    Use this on bulk or interrupt endpoints which have
+		    stalled, returning <emphasis>-EPIPE</emphasis> status
+		    to a data transfer request.
+		    Do not issue the control request directly, since
+		    that could invalidate the host's record of the
+		    data toggle.
+		    </para></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_CONTROL</term>
+		    <listitem><para>Issues a control request to the device.
+		    The ioctl parameter points to a structure like this:
+<programlisting>struct usbdevfs_ctrltransfer {
+        __u8   bRequestType;
+        __u8   bRequest;
+        __u16  wValue;
+        __u16  wIndex;
+        __u16  wLength;
+        __u32  timeout;  /* in milliseconds */
+        void   *data;
+};</programlisting>
+		    </para><para>
+		    The first eight bytes of this structure are the contents
+		    of the SETUP packet to be sent to the device; see the
+		    USB 2.0 specification for details.
+		    The bRequestType value is composed by combining a
+		    USB_TYPE_* value, a USB_DIR_* value, and a
+		    USB_RECIP_* value (from
+		    <emphasis>&lt;linux/usb.h&gt;</emphasis>).
+		    If wLength is nonzero, it describes the length of the data
+		    buffer, which is either written to the device
+		    (USB_DIR_OUT) or read from the device (USB_DIR_IN).
+		    </para><para>
+		    At this writing, you can't transfer more than 4 KBytes
+		    of data to or from a device; usbfs has a limit, and
+		    some host controller drivers have a limit.
+		    (That's not usually a problem.)
+		    <emphasis>Also</emphasis> there's no way to say it's
+		    not OK to get a short read back from the device.
+		    </para></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_RESET</term>
+		    <listitem><para>Does a USB level device reset.
+		    The ioctl parameter is ignored.
+		    After the reset, this rebinds all device interfaces.
+		    File modification time is not updated by this request.
+		    </para><warning><para>
+		    <emphasis>Avoid using this call</emphasis>
+		    until some usbcore bugs get fixed,
+		    since it does not fully synchronize device, interface,
+		    and driver (not just usbfs) state.
+		    </para></warning></listitem></varlistentry>
+	    
+		<varlistentry><term>USBDEVFS_SETINTERFACE</term>
+		    <listitem><para>Sets the alternate setting for an
+		    interface.  The ioctl parameter is a pointer to a
+		    structure like this:
+<programlisting>struct usbdevfs_setinterface {
+        unsigned int  interface;
+        unsigned int  altsetting;
+}; </programlisting>
+		    File modification time is not updated by this request.
+		    </para><para>
+		    Those struct members are from some interface descriptor
+		    applying to the the current configuration.
+		    The interface number is the bInterfaceNumber value, and
+		    the altsetting number is the bAlternateSetting value.
+		    (This resets each endpoint in the interface.)
+		    </para></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_SETCONFIGURATION</term>
+		    <listitem><para>Issues the
+		    <function>usb_set_configuration</function> call
+		    for the device.
+		    The parameter is an integer holding the number of
+		    a configuration (bConfigurationValue from descriptor).
+		    File modification time is not updated by this request.
+		    </para><warning><para>
+		    <emphasis>Avoid using this call</emphasis>
+		    until some usbcore bugs get fixed,
+		    since it does not fully synchronize device, interface,
+		    and driver (not just usbfs) state.
+		    </para></warning></listitem></varlistentry>
+
+		</variablelist>
+	    </sect2>
+
+	    <sect2>
+		<title>Asynchronous I/O Support</title>
+
+		<para>As mentioned above, there are situations where it may be
+		important to initiate concurrent operations from user mode code.
+		This is particularly important for periodic transfers
+		(interrupt and isochronous), but it can be used for other
+		kinds of USB requests too.
+		In such cases, the asynchronous requests described here
+		are essential.  Rather than submitting one request and having
+		the kernel block until it completes, the blocking is separate.
+		</para>
+
+		<para>These requests are packaged into a structure that
+		resembles the URB used by kernel device drivers.
+		(No POSIX Async I/O support here, sorry.)
+		It identifies the endpoint type (USBDEVFS_URB_TYPE_*),
+		endpoint (number, masked with USB_DIR_IN as appropriate),
+		buffer and length, and a user "context" value serving to
+		uniquely identify each request.
+		(It's usually a pointer to per-request data.)
+		Flags can modify requests (not as many as supported for
+		kernel drivers).
+		</para>
+
+		<para>Each request can specify a realtime signal number
+		(between SIGRTMIN and SIGRTMAX, inclusive) to request a
+		signal be sent when the request completes.
+		</para>
+
+		<para>When usbfs returns these urbs, the status value
+		is updated, and the buffer may have been modified.
+		Except for isochronous transfers, the actual_length is
+		updated to say how many bytes were transferred; if the
+		USBDEVFS_URB_DISABLE_SPD flag is set
+		("short packets are not OK"), if fewer bytes were read
+		than were requested then you get an error report.
+		</para>
+
+<programlisting>struct usbdevfs_iso_packet_desc {
+        unsigned int                     length;
+        unsigned int                     actual_length;
+        unsigned int                     status;
+};
+
+struct usbdevfs_urb {
+        unsigned char                    type;
+        unsigned char                    endpoint;
+        int                              status;
+        unsigned int                     flags;
+        void                             *buffer;
+        int                              buffer_length;
+        int                              actual_length;
+        int                              start_frame;
+        int                              number_of_packets;
+        int                              error_count;
+        unsigned int                     signr;
+        void                             *usercontext;
+        struct usbdevfs_iso_packet_desc  iso_frame_desc[];
+};</programlisting>
+
+		<para> For these asynchronous requests, the file modification
+		time reflects when the request was initiated.
+		This contrasts with their use with the synchronous requests,
+		where it reflects when requests complete.
+		</para>
+
+		<variablelist>
+
+		<varlistentry><term>USBDEVFS_DISCARDURB</term>
+		    <listitem><para>
+		    <emphasis>TBS</emphasis>
+		    File modification time is not updated by this request.
+		    </para><para>
+		    </para></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_DISCSIGNAL</term>
+		    <listitem><para>
+		    <emphasis>TBS</emphasis>
+		    File modification time is not updated by this request.
+		    </para><para>
+		    </para></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_REAPURB</term>
+		    <listitem><para>
+		    <emphasis>TBS</emphasis>
+		    File modification time is not updated by this request.
+		    </para><para>
+		    </para></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_REAPURBNDELAY</term>
+		    <listitem><para>
+		    <emphasis>TBS</emphasis>
+		    File modification time is not updated by this request.
+		    </para><para>
+		    </para></listitem></varlistentry>
+
+		<varlistentry><term>USBDEVFS_SUBMITURB</term>
+		    <listitem><para>
+		    <emphasis>TBS</emphasis>
+		    </para><para>
+		    </para></listitem></varlistentry>
+
+		</variablelist>
+	    </sect2>
+
+	</sect1>
+
+    </chapter>
+
+</book>
+<!-- vim:syntax=sgml:sw=4
+-->