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* seq_buf: Fix kernel documentationAndy Shevchenko2024-02-151-17/+18
| | | | | | | | | | | | | | | | | | There are plenty of issues with the kernel documentation here: - misspelled word "sequence" - different style of returned value descriptions - missed Return sections - unaligned style of ASCII / NUL-terminated / etc - wrong function references Fix all these. Link: https://lkml.kernel.org/r/20240215152506.598340-1-andriy.shevchenko@linux.intel.com Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Reviewed-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
* seq_buf: Don't use "proxy" headersAndy Shevchenko2024-02-151-2/+12
| | | | | | | | | | | | Update header inclusions to follow IWYU (Include What You Use) principle. Link: https://lkml.kernel.org/r/20240215142255.400264-1-andriy.shevchenko@linux.intel.com Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
* seq_buf: Export seq_buf_puts()Christophe JAILLET2023-11-021-0/+1
| | | | | | | | | | Mark seq_buf_puts() which is part of the seq_buf API to be exported to kernel loadable GPL modules. Link: https://lkml.kernel.org/r/b9e3737f66ec2450221b492048ce0d9c65c84953.1698861216.git.christophe.jaillet@wanadoo.fr Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
* seq_buf: Export seq_buf_putc()Christophe JAILLET2023-11-021-0/+1
| | | | | | | | | | Mark seq_buf_putc() which is part of the seq_buf API to be exported to kernel loadable GPL modules. Link: https://lkml.kernel.org/r/5c9a5ed97ac37dbdcd9c1e7bcbdec9ac166e79be.1698861216.git.christophe.jaillet@wanadoo.fr Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
* seq_buf: Introduce DECLARE_SEQ_BUF and seq_buf_str()Kees Cook2023-10-281-3/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Solve two ergonomic issues with struct seq_buf; 1) Too much boilerplate is required to initialize: struct seq_buf s; char buf[32]; seq_buf_init(s, buf, sizeof(buf)); Instead, we can build this directly on the stack. Provide DECLARE_SEQ_BUF() macro to do this: DECLARE_SEQ_BUF(s, 32); 2) %NUL termination is fragile and requires 2 steps to get a valid C String (and is a layering violation exposing the "internals" of seq_buf): seq_buf_terminate(s); do_something(s->buffer); Instead, we can just return s->buffer directly after terminating it in the refactored seq_buf_terminate(), now known as seq_buf_str(): do_something(seq_buf_str(s)); Link: https://lore.kernel.org/linux-trace-kernel/20231027155634.make.260-kees@kernel.org Link: https://lore.kernel.org/linux-trace-kernel/20231026194033.it.702-kees@kernel.org/ Cc: Yosry Ahmed <yosryahmed@google.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Justin Stitt <justinstitt@google.com> Cc: Kent Overstreet <kent.overstreet@linux.dev> Cc: Petr Mladek <pmladek@suse.com> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: Sergey Senozhatsky <senozhatsky@chromium.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Yun Zhou <yun.zhou@windriver.com> Cc: Jacob Keller <jacob.e.keller@intel.com> Cc: Zhen Lei <thunder.leizhen@huawei.com> Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
* tracing: Move readpos from seq_buf to trace_seqMatthew Wilcox (Oracle)2023-10-201-12/+10
| | | | | | | | | | | | | | | | | | | | | | To make seq_buf more lightweight as a string buf, move the readpos member from seq_buf to its container, trace_seq. That puts the responsibility of maintaining the readpos entirely in the tracing code. If some future users want to package up the readpos with a seq_buf, we can define a new struct then. Link: https://lore.kernel.org/linux-trace-kernel/20231020033545.2587554-2-willy@infradead.org Cc: Kees Cook <keescook@chromium.org> Cc: Justin Stitt <justinstitt@google.com> Cc: Kent Overstreet <kent.overstreet@linux.dev> Cc: Petr Mladek <pmladek@suse.com> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: Sergey Senozhatsky <senozhatsky@chromium.org> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
* seq_buf: Add seq_buf_do_printk() helperSergey Senozhatsky2023-04-251-0/+32
| | | | | | | | | | | | | | | | | | | | | Sometimes we use seq_buf to format a string buffer, which we then pass to printk(). However, in certain situations the seq_buf string buffer can get too big, exceeding the PRINTKRB_RECORD_MAX bytes limit, and causing printk() to truncate the string. Add a new seq_buf helper. This helper prints the seq_buf string buffer line by line, using \n as a delimiter, rather than passing the whole string buffer to printk() at once. Link: https://lkml.kernel.org/r/20230415100110.1419872-1-senozhatsky@chromium.org Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org> Reviewed-by: Petr Mladek <pmladek@suse.com> Tested-by: Yosry Ahmed <yosryahmed@google.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
* lib: fix spelling mistakesZhen Lei2021-07-081-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Fix some spelling mistakes in comments: permanentely ==> permanently wont ==> won't remaning ==> remaining succed ==> succeed shouldnt ==> shouldn't alpha-numeric ==> alphanumeric storeing ==> storing funtion ==> function documenation ==> documentation Determin ==> Determine intepreted ==> interpreted ammount ==> amount obious ==> obvious interupts ==> interrupts occured ==> occurred asssociated ==> associated taking into acount ==> taking into account squence ==> sequence stil ==> still contiguos ==> contiguous matchs ==> matches Link: https://lkml.kernel.org/r/20210607072555.12416-1-thunder.leizhen@huawei.com Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> Reviewed-by: Jacob Keller <jacob.e.keller@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* seq_buf: Make trace_seq_putmem_hex() support data longer than 8Yun Zhou2021-06-261-1/+3
| | | | | | | | | | | | | | | Since the raw memory 'data' does not go forward, it will dump repeated data if the data length is more than 8. If we want to dump longer data blocks, we need to repeatedly call macro SEQ_PUT_HEX_FIELD. I think it is a bit redundant, and multiple function calls also affect the performance. Link: https://lore.kernel.org/lkml/20210625122453.5e2fe304@oasis.local.home/ Link: https://lkml.kernel.org/r/20210626032156.47889-2-yun.zhou@windriver.com Cc: stable@vger.kernel.org Fixes: 6d2289f3faa7 ("tracing: Make trace_seq_putmem_hex() more robust") Signed-off-by: Yun Zhou <yun.zhou@windriver.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
* seq_buf: Fix overflow in seq_buf_putmem_hex()Yun Zhou2021-06-261-1/+3
| | | | | | | | | | | | | | | | There's two variables being increased in that loop (i and j), and i follows the raw data, and j follows what is being written into the buffer. We should compare 'i' to MAX_MEMHEX_BYTES or compare 'j' to HEX_CHARS. Otherwise, if 'j' goes bigger than HEX_CHARS, it will overflow the destination buffer. Link: https://lore.kernel.org/lkml/20210625122453.5e2fe304@oasis.local.home/ Link: https://lkml.kernel.org/r/20210626032156.47889-1-yun.zhou@windriver.com Cc: stable@vger.kernel.org Fixes: 5e3ca0ec76fce ("ftrace: introduce the "hex" output method") Signed-off-by: Yun Zhou <yun.zhou@windriver.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
* seq_buf: Export seq_buf_printfVaibhav Jain2020-06-151-0/+1
| | | | | | | | | | | | | | | | | | | | | | 'seq_buf' provides a very useful abstraction for writing to a string buffer without needing to worry about it over-flowing. However even though the API has been stable for couple of years now its still not exported to kernel loadable modules limiting its usage. Hence this patch proposes update to 'seq_buf.c' to mark seq_buf_printf() which is part of the seq_buf API to be exported to kernel loadable GPL modules. This symbol will be used in later parts of this patch-set to simplify content creation for a sysfs attribute. Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Cc: Piotr Maziarz <piotrx.maziarz@linux.intel.com> Cc: Cezary Rojewski <cezary.rojewski@intel.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Borislav Petkov <bp@alien8.de> Link: https://lore.kernel.org/r/20200615124407.32596-3-vaibhav@linux.ibm.com Signed-off-by: Dan Williams <dan.j.williams@intel.com>
* seq_buf: Add printing formatted hex dumpsPiotr Maziarz2019-11-141-0/+62
| | | | | | | | | | | | | | | | | | | | | | | | | | Provided function is an analogue of print_hex_dump(). Implementing this function in seq_buf allows using for multiple purposes (e.g. for tracing) and therefore prevents from code duplication in every layer that uses seq_buf. print_hex_dump() is an essential part of logging data to dmesg. Adding similar capability for other purposes is beneficial to all users. Example usage: seq_buf_hex_dump(seq, "", DUMP_PREFIX_OFFSET, 16, 4, buf, ARRAY_SIZE(buf), true); Example output: 00000000: 00000000 ffffff10 ffffff32 ffff3210 ........2....2.. 00000010: ffff3210 83d00437 c0700000 00000000 .2..7.....p..... 00000020: 02010004 0000000f 0000000f 00004002 .............@.. 00000030: 00000fff 00000000 ........ Link: http://lkml.kernel.org/r/1573130738-29390-1-git-send-email-piotrx.maziarz@linux.intel.com Signed-off-by: Piotr Maziarz <piotrx.maziarz@linux.intel.com> Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
* seq_buf: Use size_t for len in seq_buf_puts()Michael Ellerman2018-12-221-1/+1
| | | | | | | | | | | | | | | Jann Horn points out that we're using unsigned int for len in seq_buf_puts(), which could potentially overflow if we're passed a UINT_MAX sized string. The rest of the code already uses size_t, so we should also use that in seq_buf_puts() to avoid any issues. Link: http://lkml.kernel.org/r/20181019042109.8064-2-mpe@ellerman.id.au Suggested-by: Jann Horn <jannh@google.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
* seq_buf: Make seq_buf_puts() null-terminate the bufferMichael Ellerman2018-12-221-1/+5
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently seq_buf_puts() will happily create a non null-terminated string for you in the buffer. This is particularly dangerous if the buffer is on the stack. For example: char buf[8]; char secret = "secret"; struct seq_buf s; seq_buf_init(&s, buf, sizeof(buf)); seq_buf_puts(&s, "foo"); printk("Message is %s\n", buf); Can result in: Message is fooªªªªªsecret We could require all users to memset() their buffer to zero before use. But that seems likely to be forgotten and lead to bugs. Instead we can change seq_buf_puts() to always leave the buffer in a null-terminated state. The only downside is that this makes the buffer 1 character smaller for seq_buf_puts(), but that seems like a good trade off. Link: http://lkml.kernel.org/r/20181019042109.8064-1-mpe@ellerman.id.au Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
* License cleanup: add SPDX GPL-2.0 license identifier to files with no licenseGreg Kroah-Hartman2017-11-021-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Many source files in the tree are missing licensing information, which makes it harder for compliance tools to determine the correct license. By default all files without license information are under the default license of the kernel, which is GPL version 2. Update the files which contain no license information with the 'GPL-2.0' SPDX license identifier. The SPDX identifier is a legally binding shorthand, which can be used instead of the full boiler plate text. This patch is based on work done by Thomas Gleixner and Kate Stewart and Philippe Ombredanne. How this work was done: Patches were generated and checked against linux-4.14-rc6 for a subset of the use cases: - file had no licensing information it it. - file was a */uapi/* one with no licensing information in it, - file was a */uapi/* one with existing licensing information, Further patches will be generated in subsequent months to fix up cases where non-standard license headers were used, and references to license had to be inferred by heuristics based on keywords. The analysis to determine which SPDX License Identifier to be applied to a file was done in a spreadsheet of side by side results from of the output of two independent scanners (ScanCode & Windriver) producing SPDX tag:value files created by Philippe Ombredanne. Philippe prepared the base worksheet, and did an initial spot review of a few 1000 files. The 4.13 kernel was the starting point of the analysis with 60,537 files assessed. Kate Stewart did a file by file comparison of the scanner results in the spreadsheet to determine which SPDX license identifier(s) to be applied to the file. She confirmed any determination that was not immediately clear with lawyers working with the Linux Foundation. Criteria used to select files for SPDX license identifier tagging was: - Files considered eligible had to be source code files. - Make and config files were included as candidates if they contained >5 lines of source - File already had some variant of a license header in it (even if <5 lines). All documentation files were explicitly excluded. The following heuristics were used to determine which SPDX license identifiers to apply. - when both scanners couldn't find any license traces, file was considered to have no license information in it, and the top level COPYING file license applied. For non */uapi/* files that summary was: SPDX license identifier # files ---------------------------------------------------|------- GPL-2.0 11139 and resulted in the first patch in this series. If that file was a */uapi/* path one, it was "GPL-2.0 WITH Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was: SPDX license identifier # files ---------------------------------------------------|------- GPL-2.0 WITH Linux-syscall-note 930 and resulted in the second patch in this series. - if a file had some form of licensing information in it, and was one of the */uapi/* ones, it was denoted with the Linux-syscall-note if any GPL family license was found in the file or had no licensing in it (per prior point). Results summary: SPDX license identifier # files ---------------------------------------------------|------ GPL-2.0 WITH Linux-syscall-note 270 GPL-2.0+ WITH Linux-syscall-note 169 ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21 ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17 LGPL-2.1+ WITH Linux-syscall-note 15 GPL-1.0+ WITH Linux-syscall-note 14 ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5 LGPL-2.0+ WITH Linux-syscall-note 4 LGPL-2.1 WITH Linux-syscall-note 3 ((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3 ((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1 and that resulted in the third patch in this series. - when the two scanners agreed on the detected license(s), that became the concluded license(s). - when there was disagreement between the two scanners (one detected a license but the other didn't, or they both detected different licenses) a manual inspection of the file occurred. - In most cases a manual inspection of the information in the file resulted in a clear resolution of the license that should apply (and which scanner probably needed to revisit its heuristics). - When it was not immediately clear, the license identifier was confirmed with lawyers working with the Linux Foundation. - If there was any question as to the appropriate license identifier, the file was flagged for further research and to be revisited later in time. In total, over 70 hours of logged manual review was done on the spreadsheet to determine the SPDX license identifiers to apply to the source files by Kate, Philippe, Thomas and, in some cases, confirmation by lawyers working with the Linux Foundation. Kate also obtained a third independent scan of the 4.13 code base from FOSSology, and compared selected files where the other two scanners disagreed against that SPDX file, to see if there was new insights. The Windriver scanner is based on an older version of FOSSology in part, so they are related. Thomas did random spot checks in about 500 files from the spreadsheets for the uapi headers and agreed with SPDX license identifier in the files he inspected. For the non-uapi files Thomas did random spot checks in about 15000 files. In initial set of patches against 4.14-rc6, 3 files were found to have copy/paste license identifier errors, and have been fixed to reflect the correct identifier. Additionally Philippe spent 10 hours this week doing a detailed manual inspection and review of the 12,461 patched files from the initial patch version early this week with: - a full scancode scan run, collecting the matched texts, detected license ids and scores - reviewing anything where there was a license detected (about 500+ files) to ensure that the applied SPDX license was correct - reviewing anything where there was no detection but the patch license was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied SPDX license was correct This produced a worksheet with 20 files needing minor correction. This worksheet was then exported into 3 different .csv files for the different types of files to be modified. These .csv files were then reviewed by Greg. Thomas wrote a script to parse the csv files and add the proper SPDX tag to the file, in the format that the file expected. This script was further refined by Greg based on the output to detect more types of files automatically and to distinguish between header and source .c files (which need different comment types.) Finally Greg ran the script using the .csv files to generate the patches. Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org> Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tracing: Use seq_buf_used() in seq_buf_to_user() instead of lenJerry Snitselaar2015-12-231-2/+4
| | | | | | | | | | | | | | | commit 5ac48378414d ("tracing: Use trace_seq_used() and seq_buf_used() instead of len") changed the tracing code to use trace_seq_used() and seq_buf_used() instead of using the seq_buf len directly to avoid overflow issues, but missed a spot in seq_buf_to_user() that makes use of s->len. Cleaned up the code a bit as well per suggestion of Steve Rostedt. Link: http://lkml.kernel.org/r/1447703848-2951-1-git-send-email-jsnitsel@redhat.com Signed-off-by: Jerry Snitselaar <jsnitsel@redhat.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
* seq_buf: Fix seq_buf_bprintf() truncationSteven Rostedt (Red Hat)2015-03-041-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In seq_buf_bprintf(), bstr_printf() is used to copy the format into the buffer remaining in the seq_buf structure. The return of bstr_printf() is the amount of characters written to the buffer excluding the '\0', unless the line was truncated! If the line copied does not fit, it is truncated, and a '\0' is added to the end of the buffer. But in this case, '\0' is included in the length of the line written. To know if the buffer had overflowed, the return length will be the same or greater than the length of the buffer passed in. The check in seq_buf_bprintf() only checked if the length returned from bstr_printf() would fit in the buffer, as the seq_buf_bprintf() is only to be an all or nothing command. It either writes all the string into the seq_buf, or none of it. If the string is truncated, the pointers inside the seq_buf must be reset to what they were when the function was called. This is not the case. On overflow, it copies only part of the string. The fix is to change the overflow check to see if the length returned from bstr_printf() is less than the length remaining in the seq_buf buffer, and not if it is less than or equal to as it currently does. Then seq_buf_bprintf() will know if the write from bstr_printf() was truncated or not. Link: http://lkml.kernel.org/r/1425500481.2712.27.camel@perches.com Cc: stable@vger.kernel.org Reported-by: Joe Perches <joe@perches.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
* seq_buf: Fix seq_buf_vprintf() truncationSteven Rostedt (Red Hat)2015-03-041-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | In seq_buf_vprintf(), vsnprintf() is used to copy the format into the buffer remaining in the seq_buf structure. The return of vsnprintf() is the amount of characters written to the buffer excluding the '\0', unless the line was truncated! If the line copied does not fit, it is truncated, and a '\0' is added to the end of the buffer. But in this case, '\0' is included in the length of the line written. To know if the buffer had overflowed, the return length will be the same as the length of the buffer passed in. The check in seq_buf_vprintf() only checked if the length returned from vsnprintf() would fit in the buffer, as the seq_buf_vprintf() is only to be an all or nothing command. It either writes all the string into the seq_buf, or none of it. If the string is truncated, the pointers inside the seq_buf must be reset to what they were when the function was called. This is not the case. On overflow, it copies only part of the string. The fix is to change the overflow check to see if the length returned from vsnprintf() is less than the length remaining in the seq_buf buffer, and not if it is less than or equal to as it currently does. Then seq_buf_vprintf() will know if the write from vsnpritnf() was truncated or not. Cc: stable@vger.kernel.org Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
* bitmap, cpumask, nodemask: remove dedicated formatting functionsTejun Heo2015-02-131-36/+0
| | | | | | | | | | | | | | | | | Now that all bitmap formatting usages have been converted to '%*pb[l]', the separate formatting functions are unnecessary. The following functions are removed. * bitmap_scn[list]printf() * cpumask_scnprintf(), cpulist_scnprintf() * [__]nodemask_scnprintf(), [__]nodelist_scnprintf() * seq_bitmap[_list](), seq_cpumask[_list](), seq_nodemask[_list]() * seq_buf_bitmask() Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* seq_buf: Move the seq_buf code to lib/Steven Rostedt (Red Hat)2014-11-191-0/+359
The seq_buf functions are rather useful outside of tracing. Instead of having it be dependent on CONFIG_TRACING, move the code into lib/ and allow other users to have access to it even when tracing is not configured. The seq_buf utility is similar to the seq_file utility, but instead of writing sending data back up to userland, it writes it into a buffer defined at seq_buf_init(). This allows us to send a descriptor around that writes printf() formatted strings into it that can be retrieved later. It is currently used by the tracing facility for such things like trace events to convert its binary saved data in the ring buffer into an ASCII human readable context to be displayed in /sys/kernel/debug/trace. It can also be used for doing NMI prints safely from NMI context into the seq_buf and retrieved later and dumped to printk() safely. Doing printk() from an NMI context is dangerous because an NMI can preempt a current printk() and deadlock on it. Link: http://lkml.kernel.org/p/20140619213952.058255809@goodmis.org Tested-by: Jiri Kosina <jkosina@suse.cz> Acked-by: Jiri Kosina <jkosina@suse.cz> Reviewed-by: Petr Mladek <pmladek@suse.cz> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>