bcache: comment on direct access to bvec table
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>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 81e8dc3..02a4cf6 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -432,6 +432,7 @@
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 e548b8b..61813d2 100644
--- a/drivers/md/bcache/util.c
+++ b/drivers/md/bcache/util.c
@@ -249,6 +249,13 @@
: 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;