Commit 2bc5565286121d2a77ccd728eb3484dff2035b58 (Btrfs: don't update atime on
RO subvolumes) ensures that the access time of an inode is not updated when
the inode lives in a read-only subvolume.
However, if a directory on a read-only subvolume is accessed, the atime is
updated. This results in a write operation to a read-only subvolume. I
believe that access times should never be updated on read-only subvolumes.
To reproduce:
# mkfs.btrfs -f /dev/dm-3
(...)
# mount /dev/dm-3 /mnt
# btrfs subvol create /mnt/sub
Create subvolume '/mnt/sub'
# mkdir /mnt/sub/dir
# echo "abc" > /mnt/sub/dir/file
# btrfs subvol snapshot -r /mnt/sub /mnt/rosnap
Create a readonly snapshot of '/mnt/sub' in '/mnt/rosnap'
# stat /mnt/rosnap/dir
File: `/mnt/rosnap/dir'
Size: 8 Blocks: 0 IO Block: 4096 directory
Device: 16h/22d Inode: 257 Links: 1
Access: (0755/drwxr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2013-09-11 07:21:49.389157126 -0400
Modify: 2013-09-11 07:22:02.330156079 -0400
Change: 2013-09-11 07:22:02.330156079 -0400
# ls /mnt/rosnap/dir
file
# stat /mnt/rosnap/dir
File: `/mnt/rosnap/dir'
Size: 8 Blocks: 0 IO Block: 4096 directory
Device: 16h/22d Inode: 257 Links: 1
Access: (0755/drwxr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2013-09-11 07:22:56.797151670 -0400
Modify: 2013-09-11 07:22:02.330156079 -0400
Change: 2013-09-11 07:22:02.330156079 -0400
Reported-by: Koen De Wit <koen.de.wit@xxxxxxxxxx>
Signed-off-by: Guangyu Sun <guangyu.sun@xxxxxxxxxx>
---
fs/btrfs/inode.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index b7c2487..12c2755 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8660,11 +8660,13 @@ static const struct inode_operations btrfs_dir_inode_operations = {
.removexattr = btrfs_removexattr,
.permission = btrfs_permission,
.get_acl = btrfs_get_acl,
+ .update_time = btrfs_update_time,
};
static const struct inode_operations btrfs_dir_ro_inode_operations = {
.lookup = btrfs_lookup,
.permission = btrfs_permission,
.get_acl = btrfs_get_acl,
+ .update_time = btrfs_update_time,
};
static const struct file_operations btrfs_dir_file_operations = {
--
1.7.9.5
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