block: makes bio_split support bio without data

discard bio hasn't data attached. We hit a BUG_ON with such bio. This makes
bio_split works for such bio.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/bio.c b/fs/bio.c
index f855e0e..9298c65 100644 (file)
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -1475,7 +1475,7 @@ struct bio_pair *bio_split(struct bio *bi, int first_sectors)
        trace_block_split(bdev_get_queue(bi->bi_bdev), bi,
                                bi->bi_sector + first_sectors);
 
-       BUG_ON(bi->bi_vcnt != 1);
+       BUG_ON(bi->bi_vcnt != 1 && bi->bi_vcnt != 0);
        BUG_ON(bi->bi_idx != 0);
        atomic_set(&bp->cnt, 3);
        bp->error = 0;
@@ -1485,20 +1485,22 @@ struct bio_pair *bio_split(struct bio *bi, int first_sectors)
        bp->bio2.bi_size -= first_sectors << 9;
        bp->bio1.bi_size = first_sectors << 9;
 
-       bp->bv1 = bi->bi_io_vec[0];
-       bp->bv2 = bi->bi_io_vec[0];
+       if (bi->bi_vcnt != 0) {
+               bp->bv1 = bi->bi_io_vec[0];
+               bp->bv2 = bi->bi_io_vec[0];
 
-       if (bio_is_rw(bi)) {
-               bp->bv2.bv_offset += first_sectors << 9;
-               bp->bv2.bv_len -= first_sectors << 9;
-               bp->bv1.bv_len = first_sectors << 9;
-       }
+               if (bio_is_rw(bi)) {
+                       bp->bv2.bv_offset += first_sectors << 9;
+                       bp->bv2.bv_len -= first_sectors << 9;
+                       bp->bv1.bv_len = first_sectors << 9;
+               }
 
-       bp->bio1.bi_io_vec = &bp->bv1;
-       bp->bio2.bi_io_vec = &bp->bv2;
+               bp->bio1.bi_io_vec = &bp->bv1;
+               bp->bio2.bi_io_vec = &bp->bv2;
 
-       bp->bio1.bi_max_vecs = 1;
-       bp->bio2.bi_max_vecs = 1;
+               bp->bio1.bi_max_vecs = 1;
+               bp->bio2.bi_max_vecs = 1;
+       }
 
        bp->bio1.bi_end_io = bio_pair_end_1;
        bp->bio2.bi_end_io = bio_pair_end_2;