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From: John Ogness <john.ogness@linutronix.de>
Date: Mon, 6 Nov 2023 15:01:58 +0000
Subject: [PATCH 092/134] printk: ringbuffer: Cleanup reader terminology
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
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>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/printk/printk_ringbuffer.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -1987,11 +1987,13 @@ u64 prb_first_seq(struct printk_ringbuff
}
/*
- * 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)
@@ -2010,7 +2012,7 @@ static bool _prb_read_valid(struct print
*seq = tail_seq;
} else if (err == -ENOENT) {
- /* Record exists, but no data available. Skip. */
+ /* Record exists, but the data was lost. Skip. */
(*seq)++;
} else {
@@ -2043,7 +2045,7 @@ static bool _prb_read_valid(struct print
* 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)
@@ -2073,7 +2075,7 @@ bool prb_read_valid(struct printk_ringbu
* 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)
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