[dm-devel] [PATCH] dm-integrity: don't write metadata if we overwrite it with the same content

[Mikulas Patocka]

If we discard already discarded blocks, we do not need to write discard
filler to the metadata, because it is already there.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>

Index: linux-2.6/drivers/md/dm-integrity.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-integrity.c
+++ linux-2.6/drivers/md/dm-integrity.c
@@ -1429,8 +1429,10 @@ static int dm_integrity_rw_tag(struct dm
 		if (op == TAG_READ) {
 			memcpy(tag, dp, to_copy);
 		} else if (op == TAG_WRITE) {
-			memcpy(dp, tag, to_copy);
-			dm_bufio_mark_partial_buffer_dirty(b, *metadata_offset, *metadata_offset + to_copy);
+			if (memcmp(dp, tag, to_copy)) {
+				memcpy(dp, tag, to_copy);
+				dm_bufio_mark_partial_buffer_dirty(b, *metadata_offset, *metadata_offset + to_copy);
+			}
 		} else {
 			/* e.g.: op == TAG_CMP */