Commit 5113cf5f authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

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: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240207134103.1357162-6-john.ogness@linutronix.de


Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
parent 5f72e52b

kernel/printk/printk_ringbuffer.c

+16 −4
Original line number Diff line number Diff line
@@ -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;

	}

kernel/printk/printk_ringbuffer.h

+15 −1
Original line number Diff line number Diff line
@@ -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	\

{				\