[PATCH v2 15/51] btrfs: comment on direct access bvec table

Ming Lei
2017-06-26T12:09:58Z

Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: David Sterba <dsterba@suse.com>
Cc: linux-btrfs@vger.kernel.org
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
fs/btrfs/compression.c | 4 ++++
fs/btrfs/inode.c | 12 ++++++++++++
2 files changed, 16 insertions(+)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 2c0b7b57fcd5..5972f74354ca 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -541,6 +541,10 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,

/* we need the actual starting offset of this extent in the file */
read_lock(&em_tree->lock);
+ /*
+ * It is still safe to retrieve the 1st page of the bio
+ * in this way after supporting multipage bvec.
+ */
em = lookup_extent_mapping(em_tree,
page_offset(bio->bi_io_vec->bv_page),
PAGE_SIZE);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4ab02b34f029..7e725d84917b 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8055,6 +8055,12 @@ static void btrfs_retry_endio_nocsum(struct bio *bio)
if (bio->bi_status)
goto end;

+ /*
+ * WARNING:
+ *
+ * With multipage bvec, the following way of direct access to
+ * bvec table is only safe if the bio includes single page.
+ */
ASSERT(bio->bi_vcnt == 1);
io_tree = &BTRFS_I(inode)->io_tree;
failure_tree = &BTRFS_I(inode)->io_failure_tree;
@@ -8146,6 +8152,12 @@ static void btrfs_retry_endio(struct bio *bio)

uptodate = 1;

+ /*
+ * WARNING:
+ *
+ * With multipage bvec, the following way of direct access to
+ * bvec table is only safe if the bio includes single page.
+ */
ASSERT(bio->bi_vcnt == 1);
ASSERT(bio->bi_io_vec->bv_len == btrfs_inode_sectorsize(done->inode));

--
2.9.4