btrfs: skip compression property for anything other than files and dirs

The compression property only has effect on regular files and directories
(so that it's propagated to files and subdirectories created inside a
directory). For any other inode type (symlink, fifo, device, socket),
it's pointless to set the compression property because it does nothing
and ends up unnecessarily wasting leaf space due to the pointless xattr
(75 or 76 bytes, depending on the compression value). Symlinks in
particular are very common (for example, I have almost 10k symlinks under
/etc, /usr and /var alone) and therefore it's worth to avoid wasting
leaf space with the compression xattr.

For example, the compression property can end up on a symlink or character
device implicitly, through inheritance from a parent directory

  $ mkdir /mnt/testdir
  $ btrfs property set /mnt/testdir compression lzo

  $ ln -s yadayada /mnt/testdir/lnk
  $ mknod /mnt/testdir/dev c 0 0

Or explicitly like this:

  $ ln -s yadayda /mnt/lnk
  $ setfattr -h -n btrfs.compression -v lzo /mnt/lnk

So skip the compression property on inodes that are neither a regular
file nor a directory.

CC: stable@vger.kernel.org # 5.4+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/btrfs/props.h b/fs/btrfs/props.h
index 2b2ac15ab788..59bea741cfcf 100644
--- a/fs/btrfs/props.h
+++ b/fs/btrfs/props.h
@@ -15,6 +15,7 @@ int btrfs_set_prop(struct btrfs_trans_handle *trans, struct inode *inode,
 		   int flags);
 int btrfs_validate_prop(const struct btrfs_inode *inode, const char *name,
 			const char *value, size_t value_len);
+bool btrfs_ignore_prop(const struct btrfs_inode *inode, const char *name);
 
 int btrfs_load_inode_props(struct inode *inode, struct btrfs_path *path);