printk: ringbuffer: add BLK_DATALESS() macro

Rather than continually needing to explicitly check @begin and @next
to identify a dataless block, introduce and use a BLK_DATALESS()
macro.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200914123354.832-3-john.ogness@linutronix.de

kernel/printk/printk_ringbuffer.c

@@ -266,6 +266,8 @@
 
 /* Determine if a logical position refers to a data-less block. */
 #define LPOS_DATALESS(lpos)		((lpos) & 1UL)
+#define BLK_DATALESS(blk)		(LPOS_DATALESS((blk)->begin) && \
+					 LPOS_DATALESS((blk)->next))
 
 /* Get the logical position at index 0 of the current wrap. */
 #define DATA_THIS_WRAP_START_LPOS(data_ring, lpos) \
@@ -1038,7 +1040,7 @@ static unsigned int space_used(struct prb_data_ring *data_ring,
 			       struct prb_data_blk_lpos *blk_lpos)
 {
 	/* Data-less blocks take no space. */
-	if (LPOS_DATALESS(blk_lpos->begin))
+	if (BLK_DATALESS(blk_lpos))
 		return 0;
 
 	if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next)) {
@@ -1071,7 +1073,7 @@ static const char *get_data(struct prb_data_ring *data_ring,
 	struct prb_data_block *db;
 
 	/* Data-less data block description. */
-	if (LPOS_DATALESS(blk_lpos->begin) && LPOS_DATALESS(blk_lpos->next)) {
+	if (BLK_DATALESS(blk_lpos)) {
 		if (blk_lpos->begin == NO_LPOS && blk_lpos->next == NO_LPOS) {
 			*data_size = 0;
 			return "";