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printk: ringbuffer: Cleanup reader terminology

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BugLink: https://bugs.launchpad.net/bugs/2060097

[ Upstream commit 584528d621459d1a5c31da7a591218ad3bb96d6c ]

With the lockless ringbuffer, it is allowed that multiple
CPUs/contexts write simultaneously into the buffer. This creates
an ambiguity as some writers will finalize sooner.

The documentation for the prb_read functions is not clear as it
refers to "not yet written" and "no data available". Clarify the
return values and language to be in terms of the reader: records
available for reading.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240207134103.1357162-9-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>
Stable-dep-of: b1c4c67a5e90 ("printk: ringbuffer: Skip non-finalized records in panic")
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit 411d1efc4b13fc05be36bb0ff71ad2dd427e6de3)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
This commit is contained in:
John Ogness
2024-02-07 14:46:57 +01:06
committed by Roxana Nicolescu
parent 01f6337b0e
commit 9a221ccb89
1 changed files with 9 additions and 7 deletions
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kernel/printk/printk_ringbuffer.c
+9 -7
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@@ -2080,11 +2080,13 @@ try_again:
}
/*
* Non-blocking read of a record. Updates @seq to the last finalized record
* (which may have no data available).
* Non-blocking read of a record.
*
* See the description of prb_read_valid() and prb_read_valid_info()
* for details.
* On success @seq is updated to the record that was read and (if provided)
* @r and @line_count will contain the read/calculated data.
*
* On failure @seq is updated to a record that is not yet available to the
* reader, but it will be the next record available to the reader.
*/
static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
struct printk_record *r, unsigned int *line_count)
@@ -2103,7 +2105,7 @@ static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
*seq = tail_seq;
} else if (err == -ENOENT) {
/* Record exists, but no data available. Skip. */
/* Record exists, but the data was lost. Skip. */
(*seq)++;
} else {
@@ -2136,7 +2138,7 @@ static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
* On success, the reader must check r->info.seq to see which record was
* actually read. This allows the reader to detect dropped records.
*
* Failure means @seq refers to a not yet written record.
* Failure means @seq refers to a record not yet available to the reader.
*/
bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq,
struct printk_record *r)
@@ -2166,7 +2168,7 @@ bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq,
* On success, the reader must check info->seq to see which record meta data
* was actually read. This allows the reader to detect dropped records.
*
* Failure means @seq refers to a not yet written record.
* Failure means @seq refers to a record not yet available to the reader.
*/
bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq,
struct printk_info *info, unsigned int *line_count)