From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
- Move errseq.rst into core-api
- Add errseq to the core-api index
- Promote the header to a more prominent header type, otherwise we get three
entries in the table of contents.
- Reformat the table to look nicer and be a little more proportional in
terms of horizontal width per bit (the SF bit is still disproportionately
large, but there's no way to fix that).
- Include errseq kernel-doc in the errseq.rst
- Neaten some kernel-doc markup
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
Documentation/{ => core-api}/errseq.rst | 20 +++++++++++++-----
Documentation/core-api/index.rst | 1 +
include/linux/errseq.h | 2 +-
lib/errseq.c | 37 +++++++++++++++++++--------------
4 files changed, 38 insertions(+), 22 deletions(-)
rename Documentation/{ => core-api}/errseq.rst (92%)
diff --git a/Documentation/errseq.rst b/Documentation/core-api/errseq.rst
similarity index 92%
rename from Documentation/errseq.rst
rename to Documentation/core-api/errseq.rst
index 4c29bd5afbc5..ff332e272405 100644
--- a/Documentation/errseq.rst
+++ b/Documentation/core-api/errseq.rst
@@ -1,5 +1,7 @@
+=====================
The errseq_t datatype
=====================
+
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.
@@ -21,12 +23,13 @@ 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.
-Thus we end up with a value that looks something like this::
+Thus we end up with a value that looks something like this:
- bit: 31..13 12 11..0
- +-----------------+----+----------------+
- | counter | SF | errno |
- +-----------------+----+----------------+
++--------------------------------------+----+------------------------+
+| 31..13 | 12 | 11..0 |
++--------------------------------------+----+------------------------+
+| counter | SF | errno |
++--------------------------------------+----+------------------------+
The general idea is for "watchers" to sample an errseq_t value and keep
it as a running cursor. That value can later be used to tell whether
@@ -42,6 +45,7 @@ has ever been an error set since it was first initialized.
API usage
=========
+
Let me tell you a story about a worker drone. Now, he's a good worker
overall, but the company is a little...management heavy. He has to
report to 77 supervisors today, and tomorrow the "big boss" is coming in
@@ -125,6 +129,7 @@ not usable by anyone else.
Serializing errseq_t cursor updates
===================================
+
Note that the errseq_t API does not protect the errseq_t cursor during a
check_and_advance_operation. Only the canonical error code is handled
atomically. In a situation where more than one task might be using the
@@ -147,3 +152,8 @@ errseq_check_and_advance after taking the lock. e.g.::
That avoids the spinlock in the common case where nothing has changed
since the last time it was checked.
+
+Functions
+=========
+
+.. kernel-doc:: lib/errseq.c
diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst
index eb16ba30aeb6..b226d05df1c3 100644
--- a/Documentation/core-api/index.rst
+++ b/Documentation/core-api/index.rst
@@ -22,6 +22,7 @@ Core utilities
flexible-arrays
librs
genalloc
+ errseq
Interfaces for kernel debugging
===============================
diff --git a/include/linux/errseq.h b/include/linux/errseq.h
index 6ffae9c5052d..fc2777770768 100644
--- a/include/linux/errseq.h
+++ b/include/linux/errseq.h
@@ -1,6 +1,6 @@
/* SPDX-License-Identifier: GPL-2.0 */
/*
- * See Documentation/errseq.rst and lib/errseq.c
+ * See Documentation/core-api/errseq.rst and lib/errseq.c
*/
#ifndef _LINUX_ERRSEQ_H
#define _LINUX_ERRSEQ_H
diff --git a/lib/errseq.c b/lib/errseq.c
index 79cc66897db4..df782418b333 100644
--- a/lib/errseq.c
+++ b/lib/errseq.c
@@ -46,14 +46,14 @@
* @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
+ * 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.
*
- * We do return the latest value here, 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.
+ * 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)
{
@@ -108,11 +108,13 @@ errseq_t errseq_set(errseq_t *eseq, int err)
EXPORT_SYMBOL(errseq_set);
/**
- * errseq_sample - grab current errseq_t value
- * @eseq: pointer to errseq_t to be sampled
+ * errseq_sample() - Grab current errseq_t value.
+ * @eseq: Pointer to errseq_t to be sampled.
*
* This function allows callers to sample an errseq_t value, marking it as
* "seen" if required.
+ *
+ * Return: The current errseq value.
*/
errseq_t errseq_sample(errseq_t *eseq)
{
@@ -134,15 +136,15 @@ errseq_t errseq_sample(errseq_t *eseq)
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
+ * 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
+ * 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.
*
- * Returns the latest error set in the errseq_t or 0 if it hasn't changed.
+ * 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)
{
@@ -155,11 +157,11 @@ int errseq_check(errseq_t *eseq, errseq_t since)
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
+ * 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"
+ * 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
@@ -170,6 +172,9 @@ EXPORT_SYMBOL(errseq_check);
* 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)
{
--
2.15.1
--
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