[lvm-devel] [PATCH] use snapshot metadata usage to determine if snapshot is empty

[Mike Snitzer]

Future dm-snapshot will append metadata sectors used to a snapshot's
status.  This patch allows LVM2 to accurately determine if the snapshot
store is empty.  Knowing when a snapshot store is empty is important in
the context of snapshot-merge (means merge is complete).

Signed-off-by: Mike Snitzer <snitzer at redhat.com>
---
diff --git a/lib/snapshot/snapshot.c b/lib/snapshot/snapshot.c
index d5bac31..6c61cf0 100644
--- a/lib/snapshot/snapshot.c
+++ b/lib/snapshot/snapshot.c
@@ -95,15 +95,17 @@ static int _snap_target_percent(void **target_state __attribute((unused)),
 				char *params, uint64_t *total_numerator,
 				uint64_t *total_denominator)
 {
-	uint64_t numerator, denominator;
+	uint64_t total_sectors, sectors_allocated, metadata_sectors = 0;
+	int r;
 
-	if (sscanf(params, "%" PRIu64 "/%" PRIu64,
-		   &numerator, &denominator) == 2) {
-		*total_numerator += numerator;
-		*total_denominator += denominator;
-		if (!numerator)
+	r = sscanf(params, "%" PRIu64 "/%" PRIu64 " %" PRIu64, 
+		   &sectors_allocated, &total_sectors, &metadata_sectors);
+	if (r == 2 || r == 3) {
+		*total_numerator += sectors_allocated;
+		*total_denominator += total_sectors;
+		if (sectors_allocated == metadata_sectors)
 			*percent_range = PERCENT_0;
-		else if (numerator == denominator)
+		else if (sectors_allocated == total_sectors)
 			*percent_range = PERCENT_100;
 		else
 			*percent_range = PERCENT_0_TO_100;