block: Ensure we only enable integrity metadata for reads and writes

We'd occasionally attempt to generate protection information for flushes
and other requests with a zero payload. Make sure we only attempt to
enable integrity for reads and writes.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

fs/bio-integrity.c

@@ -182,6 +182,9 @@ static int bdev_integrity_enabled(struct block_device *bdev, int rw)
  */
 int bio_integrity_enabled(struct bio *bio)
 {
+	if (!bio_is_rw(bio))
+		return 0;
+
 	/* Already protected? */
 	if (bio_integrity(bio))
 		return 0;