block: Find bio sector offset given idx and offset

Helper function to find the sector offset in a bio given bvec index
and page offset.

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

1 files changed, 36 insertions, 0 deletions

diff --git a/fs/bio.c b/fs/bio.c
index e56e7685af9..a5af5809f56 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -1300,6 +1300,42 @@ struct bio_pair *bio_split(struct bio *bi, mempool_t *pool, int first_sectors)
 	return bp;
 }
 
+/**
+ *      bio_sector_offset - Find hardware sector offset in bio
+ *      @bio:           bio to inspect
+ *      @index:         bio_vec index
+ *      @offset:        offset in bv_page
+ *
+ *      Return the number of hardware sectors between beginning of bio
+ *      and an end point indicated by a bio_vec index and an offset
+ *      within that vector's page.
+ */
+sector_t bio_sector_offset(struct bio *bio, unsigned short index,
+			   unsigned int offset)
+{
+	unsigned int sector_sz = queue_hardsect_size(bio->bi_bdev->bd_disk->queue);
+	struct bio_vec *bv;
+	sector_t sectors;
+	int i;
+
+	sectors = 0;
+
+	if (index >= bio->bi_idx)
+		index = bio->bi_vcnt - 1;
+
+	__bio_for_each_segment(bv, bio, i, 0) {
+		if (i == index) {
+			if (offset > bv->bv_offset)
+				sectors += (offset - bv->bv_offset) / sector_sz;
+			break;
+		}
+
+		sectors += bv->bv_len / sector_sz;
+	}
+
+	return sectors;
+}
+EXPORT_SYMBOL(bio_sector_offset);
 
 /*
  * create memory pools for biovec's in a bio_set.