block: Immutable bio vecs

This adds a mechanism by which we can advance a bio by an arbitrary
number of bytes without modifying the biovec: bio->bi_iter.bi_bvec_done
indicates the number of bytes completed in the current bvec.

Various driver code still needs to be updated to not refer to the bvec
directly before we can use this for interesting things, like efficient
bio splitting.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Lars Ellenberg <drbd-dev@lists.linbit.com>
Cc: Paul Clements <Paul.Clements@steeleye.com>
Cc: drbd-user@lists.linbit.com
Cc: nbd-general@lists.sourceforge.net

1 files changed, 2 insertions, 25 deletions

diff --git a/fs/bio.c b/fs/bio.c
index 8b7f14a95503..07b4b7afa695 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -532,13 +532,11 @@ void __bio_clone(struct bio *bio, struct bio *bio_src)
          * most users will be overriding ->bi_bdev with a new target,
          * so we don't set nor calculate new physical/hw segment counts here
          */
-        bio->bi_iter.bi_sector = bio_src->bi_iter.bi_sector;
         bio->bi_bdev = bio_src->bi_bdev;
         bio->bi_flags |= 1 << BIO_CLONED;
         bio->bi_rw = bio_src->bi_rw;
         bio->bi_vcnt = bio_src->bi_vcnt;
-        bio->bi_iter.bi_size = bio_src->bi_iter.bi_size;
-        bio->bi_iter.bi_idx = bio_src->bi_iter.bi_idx;
+        bio->bi_iter = bio_src->bi_iter;
 }
 EXPORT_SYMBOL(__bio_clone);
 
@@ -808,28 +806,7 @@ void bio_advance(struct bio *bio, unsigned bytes)
         if (bio_integrity(bio))
                 bio_integrity_advance(bio, bytes);
 
-        bio->bi_iter.bi_sector += bytes >> 9;
-        bio->bi_iter.bi_size -= bytes;
-
-        if (bio->bi_rw & BIO_NO_ADVANCE_ITER_MASK)
-                return;
-
-        while (bytes) {
-                if (unlikely(bio->bi_iter.bi_idx >= bio->bi_vcnt)) {
-                        WARN_ONCE(1, "bio idx %d >= vcnt %d\n",
-                                  bio->bi_iter.bi_idx, bio->bi_vcnt);
-                        break;
-                }
-
-                if (bytes >= bio_iovec(bio).bv_len) {
-                        bytes -= bio_iovec(bio).bv_len;
-                        bio->bi_iter.bi_idx++;
-                } else {
-                        bio_iovec(bio).bv_len -= bytes;
-                        bio_iovec(bio).bv_offset += bytes;
-                        bytes = 0;
-                }
-        }
+        bio_advance_iter(bio, &bio->bi_iter, bytes);
 }
 EXPORT_SYMBOL(bio_advance);