block: Change bio_split() to respect the current value of bi_idx

In the current code bio_split() won't be seeing partially completed bios
so this doesn't change any behaviour, but this makes the code a bit
clearer as to what bio_split() actually requires.

The immediate purpose of the patch is removing unnecessary bi_idx
references, but the end goal is to allow partial completed bios to be
submitted, which along with immutable biovecs enables effecient bio
splitting.

Some of the callers were (double) checking that bios could be split, so
update their checks too.

Signed-off-by: Kent Overstreet <koverstreet@google.com>
CC: Jens Axboe <axboe@kernel.dk>
CC: Lars Ellenberg <drbd-dev@lists.linbit.com>
CC: Neil Brown <neilb@suse.de>
CC: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 3 insertions, 4 deletions

diff --git a/fs/bio.c b/fs/bio.c
index 7edc08d2246c..f1b4c1651089 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -1620,8 +1620,7 @@ 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 && bi->bi_vcnt != 0);
-        BUG_ON(bi->bi_idx != 0);
+        BUG_ON(bio_segments(bi) > 1);
         atomic_set(&bp->cnt, 3);
         bp->error = 0;
         bp->bio1 = *bi;
@@ -1631,8 +1630,8 @@ struct bio_pair *bio_split(struct bio *bi, int first_sectors)
         bp->bio1.bi_size = first_sectors << 9;
 
         if (bi->bi_vcnt != 0) {
-                bp->bv1 = bi->bi_io_vec[0];
-                bp->bv2 = bi->bi_io_vec[0];
+                bp->bv1 = *bio_iovec(bi);
+                bp->bv2 = *bio_iovec(bi);
 
                 if (bio_is_rw(bi)) {
                         bp->bv2.bv_offset += first_sectors << 9;