linux/lib/errseq.c

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License cleanup: add SPDX GPL-2.0 license identifier to files with no license 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>
2017-11-01 22:07:57 +08:00
// SPDX-License-Identifier: GPL-2.0
#include <linux/err.h>
#include <linux/bug.h>
#include <linux/atomic.h>
#include <linux/errseq.h>
#include <linux/log2.h>
/*
* An errseq_t is a way of recording errors in one place, and allowing any
* number of "subscribers" to tell whether it has changed since a previous
* point where it was sampled.
*
* It's implemented as an unsigned 32-bit value. The low order bits are
* designated to hold an error code (between 0 and -MAX_ERRNO). The upper bits
* are used as a counter. This is done with atomics instead of locking so that
* these functions can be called from any context.
*
* The general idea is for consumers to sample an errseq_t value. That value
* can later be used to tell whether any new errors have occurred since that
* sampling was done.
*
* Note that there is a risk of collisions if new errors are being recorded
* frequently, since we have so few bits to use as a counter.
*
* To mitigate this, one bit is used as a flag to tell whether the value has
* been sampled since a new value was recorded. That allows us to avoid bumping
* the counter if no one has sampled it since the last time an error was
* recorded.
*
* A new errseq_t should always be zeroed out. A errseq_t value of all zeroes
* is the special (but common) case where there has never been an error. An all
* zero value thus serves as the "epoch" if one wishes to know whether there
* has ever been an error set since it was first initialized.
*/
/* The low bits are designated for error code (max of MAX_ERRNO) */
#define ERRSEQ_SHIFT ilog2(MAX_ERRNO + 1)
/* This bit is used as a flag to indicate whether the value has been seen */
#define ERRSEQ_SEEN (1 << ERRSEQ_SHIFT)
/* The lowest bit of the counter */
#define ERRSEQ_CTR_INC (1 << (ERRSEQ_SHIFT + 1))
/**
* errseq_set - set a errseq_t for later reporting
* @eseq: errseq_t field that should be set
* @err: error to set (must be between -1 and -MAX_ERRNO)
*
* This function sets the error in @eseq, and increments the sequence counter
* if the last sequence was sampled at some point in the past.
*
* Any error set will always overwrite an existing error.
*
* Return: The previous value, primarily for debugging purposes. The
* return value should not be used as a previously sampled value in later
* calls as it will not have the SEEN flag set.
*/
errseq_t errseq_set(errseq_t *eseq, int err)
{
errseq_t cur, old;
/* MAX_ERRNO must be able to serve as a mask */
BUILD_BUG_ON_NOT_POWER_OF_2(MAX_ERRNO + 1);
/*
* Ensure the error code actually fits where we want it to go. If it
* doesn't then just throw a warning and don't record anything. We
* also don't accept zero here as that would effectively clear a
* previous error.
*/
old = READ_ONCE(*eseq);
if (WARN(unlikely(err == 0 || (unsigned int)-err > MAX_ERRNO),
"err = %d\n", err))
return old;
for (;;) {
errseq_t new;
/* Clear out error bits and set new error */
new = (old & ~(MAX_ERRNO|ERRSEQ_SEEN)) | -err;
/* Only increment if someone has looked at it */
if (old & ERRSEQ_SEEN)
new += ERRSEQ_CTR_INC;
/* If there would be no change, then call it done */
if (new == old) {
cur = new;
break;
}
/* Try to swap the new value into place */
cur = cmpxchg(eseq, old, new);
/*
* Call it success if we did the swap or someone else beat us
* to it for the same value.
*/
if (likely(cur == old || cur == new))
break;
/* Raced with an update, try again */
old = cur;
}
return cur;
}
EXPORT_SYMBOL(errseq_set);
/**
* errseq_sample() - Grab current errseq_t value.
* @eseq: Pointer to errseq_t to be sampled.
*
* This function allows callers to initialise their errseq_t variable.
* If the error has been "seen", new callers will not see an old error.
* If there is an unseen error in @eseq, the caller of this function will
* see it the next time it checks for an error.
*
* Context: Any context.
* Return: The current errseq value.
*/
errseq_t errseq_sample(errseq_t *eseq)
{
errseq_t old = READ_ONCE(*eseq);
/* If nobody has seen this error yet, then we can be the first. */
if (!(old & ERRSEQ_SEEN))
old = 0;
return old;
}
EXPORT_SYMBOL(errseq_sample);
/**
* errseq_check() - Has an error occurred since a particular sample point?
* @eseq: Pointer to errseq_t value to be checked.
* @since: Previously-sampled errseq_t from which to check.
*
* Grab the value that eseq points to, and see if it has changed @since
* the given value was sampled. The @since value is not advanced, so there
* is no need to mark the value as seen.
*
* Return: The latest error set in the errseq_t or 0 if it hasn't changed.
*/
int errseq_check(errseq_t *eseq, errseq_t since)
{
errseq_t cur = READ_ONCE(*eseq);
if (likely(cur == since))
return 0;
return -(cur & MAX_ERRNO);
}
EXPORT_SYMBOL(errseq_check);
/**
* errseq_check_and_advance() - Check an errseq_t and advance to current value.
* @eseq: Pointer to value being checked and reported.
* @since: Pointer to previously-sampled errseq_t to check against and advance.
*
* Grab the eseq value, and see whether it matches the value that @since
* points to. If it does, then just return 0.
*
* If it doesn't, then the value has changed. Set the "seen" flag, and try to
* swap it into place as the new eseq value. Then, set that value as the new
* "since" value, and return whatever the error portion is set to.
*
* Note that no locking is provided here for concurrent updates to the "since"
* value. The caller must provide that if necessary. Because of this, callers
* may want to do a lockless errseq_check before taking the lock and calling
* this.
*
* Return: Negative errno if one has been stored, or 0 if no new error has
* occurred.
*/
int errseq_check_and_advance(errseq_t *eseq, errseq_t *since)
{
int err = 0;
errseq_t old, new;
/*
* Most callers will want to use the inline wrapper to check this,
* so that the common case of no error is handled without needing
* to take the lock that protects the "since" value.
*/
old = READ_ONCE(*eseq);
if (old != *since) {
/*
* Set the flag and try to swap it into place if it has
* changed.
*
* We don't care about the outcome of the swap here. If the
* swap doesn't occur, then it has either been updated by a
* writer who is altering the value in some way (updating
* counter or resetting the error), or another reader who is
* just setting the "seen" flag. Either outcome is OK, and we
* can advance "since" and return an error based on what we
* have.
*/
new = old | ERRSEQ_SEEN;
if (new != old)
cmpxchg(eseq, old, new);
*since = new;
err = -(new & MAX_ERRNO);
}
return err;
}
EXPORT_SYMBOL(errseq_check_and_advance);