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>

1 files changed, 15 insertions, 1 deletions

diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h
index 2d948cc82b5b..d49460f7578e 100644
--- a/kernel/printk/printk_ringbuffer.h
+++ b/kernel/printk/printk_ringbuffer.h
@@ -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	\
 {				\