[PATCH] Btrfs: avoid setting ->d_op twice

[PATCH] Btrfs: avoid setting ->d_op twice

[Li Zefan]

Follow those instructions, and you'll trigger a warning in the
beginning of d_set_d_op():

  # mkfs.btrfs /dev/loop3
  # mount /dev/loop3 /mnt
  # btrfs sub create /mnt/sub
  # btrfs sub snap /mnt /mnt/snap
  # touch /mnt/snap/sub
  touch: cannot touch `tmp': Permission denied

__d_alloc() set d_op to sb->s_d_op (btrfs_dentry_operations), and
then simple_lookup() reset it to simple_dentry_operations, which
triggered the warning.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 fs/btrfs/inode.c |   14 +++++++++-----
 1 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 32214fe..2a623cc 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3908,7 +3908,7 @@ static struct inode *new_simple_dir(struct super_block *s,
 	BTRFS_I(inode)->dummy_inode = 1;
 
 	inode->i_ino = BTRFS_EMPTY_SUBVOL_DIR_OBJECTID;
-	inode->i_op = &simple_dir_inode_operations;
+	inode->i_op = &btrfs_dir_ro_inode_operations;
 	inode->i_fop = &simple_dir_operations;
 	inode->i_mode = S_IFDIR | S_IRUGO | S_IWUSR | S_IXUGO;
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
@@ -3979,14 +3979,18 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
 static int btrfs_dentry_delete(const struct dentry *dentry)
 {
 	struct btrfs_root *root;
+	struct inode *inode = dentry->d_inode;
 
-	if (!dentry->d_inode && !IS_ROOT(dentry))
-		dentry = dentry->d_parent;
+	if (!inode && !IS_ROOT(dentry))
+		inode = dentry->d_parent->d_inode;
 
-	if (dentry->d_inode) {
-		root = BTRFS_I(dentry->d_inode)->root;
+	if (inode) {
+		root = BTRFS_I(inode)->root;
 		if (btrfs_root_refs(&root->root_item) == 0)
 			return 1;
+
+		if (btrfs_ino(inode) == BTRFS_EMPTY_SUBVOL_DIR_OBJECTID)
+			return 1;
 	}
 	return 0;
 }
-- 
1.7.3.1

Re: [PATCH] Btrfs: avoid setting ->d_op twice

[David Sterba]

Hi,

thanks for the patch!

On Tue, Feb 21, 2012 at 05:04:28PM +0800, Li Zefan wrote:
> Follow those instructions, and you'll trigger a warning in the
> beginning of d_set_d_op():
> 
>   # mkfs.btrfs /dev/loop3
>   # mount /dev/loop3 /mnt
>   # btrfs sub create /mnt/sub
>   # btrfs sub snap /mnt /mnt/snap
>   # touch /mnt/snap/sub
>   touch: cannot touch `tmp': Permission denied

is this the right error code? permission denied == EACCESS and this is
returned in case of file

(strace touch file)

open("file", O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK, 0666) = -1 EACCES (Permission denied)

while mkdir returns (strace mkdir a-dir)

mkdir("a-dir", 0777)                    = -1 EPERM (Operation not permitted)


The commands were run as root and EPERM looks more adequate than
EACCESS.


david

Re: [PATCH] Btrfs: avoid setting ->d_op twice

[Li Zefan]

David Sterba wrote:
> Hi,
> 
> thanks for the patch!
> 
> On Tue, Feb 21, 2012 at 05:04:28PM +0800, Li Zefan wrote:
>> Follow those instructions, and you'll trigger a warning in the
>> beginning of d_set_d_op():
>>
>>   # mkfs.btrfs /dev/loop3
>>   # mount /dev/loop3 /mnt
>>   # btrfs sub create /mnt/sub
>>   # btrfs sub snap /mnt /mnt/snap
>>   # touch /mnt/snap/sub
>>   touch: cannot touch `tmp': Permission denied
> 
> is this the right error code? permission denied == EACCESS and this is
> returned in case of file
> 
> (strace touch file)
> 
> open("file", O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK, 0666) = -1 EACCES (Permission denied)
> 
> while mkdir returns (strace mkdir a-dir)
> 
> mkdir("a-dir", 0777)                    = -1 EPERM (Operation not permitted)
> 
> 
> The commands were run as root and EPERM looks more adequate than
> EACCESS.
> 

This is a different issue, and EPERM is returned by VFS not btrfs.

Feel free to submit a patch to fsdevel for discussion.