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printk: ringbuffer: Clarify special lpos values 

For empty line records, no data blocks are created. Instead,
these valid records are identified by special logical position
values (in fields of @prb_desc.text_blk_lpos).

Currently the macro NO_LPOS is used for empty line records.
This name is confusing because it does not imply _why_ there is
no data block.

Rename NO_LPOS to EMPTY_LINE_LPOS so that it is clear why there
is no data block.

Also add comments explaining the use of EMPTY_LINE_LPOS as well
as clarification to the values used to represent data-less
blocks.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240207134103.1357162-6-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>
This commit is contained in:
John Ogness 2024-02-07 14:46:54 +01:06 committed by Petr Mladek
parent 5f72e52ba9
commit 5113cf5f4c
2 changed files with 31 additions and 5 deletions
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20
kernel/printk/printk_ringbuffer.c
View File

@ -1034,9 +1034,13 @@ static char *data_alloc(struct printk_ringbuffer *rb, unsigned int size,
unsigned long next_lpos;
if (size == 0) {
/* Specify a data-less block. */
blk_lpos->begin = NO_LPOS;
blk_lpos->next = NO_LPOS;
/*
* Data blocks are not created for empty lines. Instead, the
* reader will recognize these special lpos values and handle
* it appropriately.
*/
blk_lpos->begin = EMPTY_LINE_LPOS;
blk_lpos->next = EMPTY_LINE_LPOS;
return NULL;
}
@ -1214,10 +1218,18 @@ static const char *get_data(struct prb_data_ring *data_ring,
/* Data-less data block description. */
if (BLK_DATALESS(blk_lpos)) {
if (blk_lpos->begin == NO_LPOS && blk_lpos->next == NO_LPOS) {
/*
* Records that are just empty lines are also valid, even
* though they do not have a data block. For such records
* explicitly return empty string data to signify success.
*/
if (blk_lpos->begin == EMPTY_LINE_LPOS &&
blk_lpos->next == EMPTY_LINE_LPOS) {
*data_size = 0;
return "";
}
/* Data lost, invalid, or otherwise unavailable. */
return NULL;
}

16
kernel/printk/printk_ringbuffer.h
View File

@ -127,8 +127,22 @@ enum desc_state {
#define DESC_SV(id, state) (((unsigned long)state << DESC_FLAGS_SHIFT) | id)
#define DESC_ID_MASK (~DESC_FLAGS_MASK)
#define DESC_ID(sv) ((sv) & DESC_ID_MASK)
/*
* Special data block logical position values (for fields of
* @prb_desc.text_blk_lpos).
*
* - Bit0 is used to identify if the record has no data block. (Implemented in
* the LPOS_DATALESS() macro.)
*
* - Bit1 specifies the reason for not having a data block.
*
* These special values could never be real lpos values because of the
* meta data and alignment padding of data blocks. (See to_blk_size() for
* details.)
*/
#define FAILED_LPOS 0x1
#define NO_LPOS 0x3
#define EMPTY_LINE_LPOS 0x3
#define FAILED_BLK_LPOS \
{ \