[PATCH 07/10] bcache: comment on direct access to bvec table

Ming Lei
2017-12-08T13:15:46Z

All direct access to bvec table are safe even after multipage bvec is supported.

Cc: linux-bcache@vger.kernel.org
Acked-by: Coly Li <colyli@suse.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
drivers/md/bcache/btree.c | 1 +
drivers/md/bcache/util.c | 7 +++++++
2 files changed, 8 insertions(+)

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 11c5503d31dc..c09f3dd4bf07 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -432,6 +432,7 @@ static void do_btree_node_write(struct btree *b)

continue_at(cl, btree_node_write_done, NULL);
} else {
+ /* No problem for multipage bvec since the bio is just allocated */
b->bio->bi_vcnt = 0;
bch_bio_map(b->bio, i);

diff --git a/drivers/md/bcache/util.c b/drivers/md/bcache/util.c
index e548b8b51322..61813d230015 100644
--- a/drivers/md/bcache/util.c
+++ b/drivers/md/bcache/util.c
@@ -249,6 +249,13 @@ uint64_t bch_next_delay(struct bch_ratelimit *d, uint64_t done)
: 0;
}

+/*
+ * Generally it isn't good to access .bi_io_vec and .bi_vcnt directly,
+ * the preferred way is bio_add_page, but in this case, bch_bio_map()
+ * supposes that the bvec table is empty, so it is safe to access
+ * .bi_vcnt & .bi_io_vec in this way even after multipage bvec is
+ * supported.
+ */
void bch_bio_map(struct bio *bio, void *base)
{
size_t size = bio->bi_iter.bi_size;
--
2.9.5