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Subject[PATCH v1 53/54] btrfs: comment on direct access bvec table
Date
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
fs/btrfs/compression.c | 4 ++++
fs/btrfs/inode.c | 17 +++++++++++++++++
2 files changed, 21 insertions(+)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 485a60923bba..54306dee392a 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -601,6 +601,10 @@ int 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 fa77cb210907..d0714208495f 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7914,6 +7914,11 @@ static int dio_read_error(struct inode *inode, struct bio *failed_bio,
return -EIO;
}

+ /*
+ * In this case it is still correct to retrieve length
+ * of the 1st bvec of the bio in this way after supporting
+ * multipage bvec.
+ */
if ((bio_segments_all(failed_bio) > 1)
|| (failed_bio->bi_io_vec->bv_len
> btrfs_inode_sectorsize(inode)))
@@ -7960,6 +7965,12 @@ static void btrfs_retry_endio_nocsum(struct bio *bio)
if (bio->bi_error)
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);
inode = bio->bi_io_vec->bv_page->mapping->host;
ASSERT(bio->bi_io_vec->bv_len == btrfs_inode_sectorsize(inode));
@@ -8045,6 +8056,12 @@ static void btrfs_retry_endio(struct bio *bio)

start = done->start;

+ /*
+ * 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);
inode = bio->bi_io_vec->bv_page->mapping->host;
ASSERT(bio->bi_io_vec->bv_len == btrfs_inode_sectorsize(inode));
--
2.7.4
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