[PATCH] Document bi_sector and sector_t

Signed-Off-By: NRoger Gammans <rgammans@computer-surgery.co.uk>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

include/linux/bio.h

@@ -70,7 +70,8 @@ typedef void (bio_destructor_t) (struct bio *);
  * 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 */

include/linux/types.h

@@ -129,8 +129,12 @@ typedef		__s64		int64_t;
 /* this is a special 64bit data type that is 8-byte aligned */
 #define aligned_u64 unsigned long long __attribute__((aligned(8)))
 
-/*
+/**
  * The type used for indexing onto a disc or disc partition.
+ *
+ * Linux always considers sectors to be 512 bytes long independently
+ * of the devices real block size.
+ *
  * If required, asm/types.h can override it and define
  * HAVE_SECTOR_T
  */