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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>
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@ -1034,9 +1034,13 @@ static char *data_alloc(struct printk_ringbuffer *rb, unsigned int size,
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unsigned long next_lpos;
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if (size == 0) {
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/* Specify a data-less block. */
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blk_lpos->begin = NO_LPOS;
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blk_lpos->next = NO_LPOS;
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/*
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* Data blocks are not created for empty lines. Instead, the
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* reader will recognize these special lpos values and handle
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* it appropriately.
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*/
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blk_lpos->begin = EMPTY_LINE_LPOS;
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blk_lpos->next = EMPTY_LINE_LPOS;
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return NULL;
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}
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@ -1214,10 +1218,18 @@ static const char *get_data(struct prb_data_ring *data_ring,
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/* Data-less data block description. */
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if (BLK_DATALESS(blk_lpos)) {
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if (blk_lpos->begin == NO_LPOS && blk_lpos->next == NO_LPOS) {
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/*
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* Records that are just empty lines are also valid, even
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* though they do not have a data block. For such records
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* explicitly return empty string data to signify success.
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*/
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if (blk_lpos->begin == EMPTY_LINE_LPOS &&
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blk_lpos->next == EMPTY_LINE_LPOS) {
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*data_size = 0;
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return "";
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}
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/* Data lost, invalid, or otherwise unavailable. */
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return NULL;
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}
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@ -127,8 +127,22 @@ enum desc_state {
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#define DESC_SV(id, state) (((unsigned long)state << DESC_FLAGS_SHIFT) | id)
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#define DESC_ID_MASK (~DESC_FLAGS_MASK)
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#define DESC_ID(sv) ((sv) & DESC_ID_MASK)
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/*
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* Special data block logical position values (for fields of
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* @prb_desc.text_blk_lpos).
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*
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* - Bit0 is used to identify if the record has no data block. (Implemented in
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* the LPOS_DATALESS() macro.)
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*
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* - Bit1 specifies the reason for not having a data block.
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*
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* These special values could never be real lpos values because of the
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* meta data and alignment padding of data blocks. (See to_blk_size() for
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* details.)
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*/
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#define FAILED_LPOS 0x1
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#define NO_LPOS 0x3
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#define EMPTY_LINE_LPOS 0x3
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#define FAILED_BLK_LPOS \
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{ \
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