[PATCH] Document bi_sector and sector_t

Signed-Off-By: Roger Gammans <rgammans@computer-surgery.co.uk>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 711c321..092dbd0 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -70,7 +70,8 @@
  * stacking drivers)
  */
 struct bio {
-	sector_t		bi_sector;
+	sector_t		bi_sector;	/* device address in 512 byte
+						   sectors */
 	struct bio		*bi_next;	/* request queue link */
 	struct block_device	*bi_bdev;
 	unsigned long		bi_flags;	/* status, command, etc */