Re: [PATCH 1/2] ceph: don't clobber i_snap_caps on non-I_NEW inode

[Xiubo Li <xiubli@redhat.com>]

On 2021/3/19 20:51, Jeff Layton wrote:
> On Fri, 2021-03-19 at 13:03 +0800, Xiubo Li wrote:
>> On 2021/3/16 2:07, Jeff Layton wrote:
>>> We want the snapdir to mirror the non-snapped directory's attributes for
>>> most things, but i_snap_caps represents the caps granted on the snapshot
>>> directory by the MDS itself. A misbehaving MDS could issue different
>>> caps for the snapdir and we lose them here.
>>>
>>> Only reset i_snap_caps when the inode is I_NEW.
>>>
>>> Reported-by: Al Viro <viro@zeniv.linux.org.uk>
>>> Signed-off-by: Jeff Layton <jlayton@kernel.org>
>>> ---
>>>    fs/ceph/inode.c | 7 ++++---
>>>    1 file changed, 4 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
>>> index 26dc7a296f6b..fc7f4bf63306 100644
>>> --- a/fs/ceph/inode.c
>>> +++ b/fs/ceph/inode.c
>>> @@ -101,12 +101,13 @@ struct inode *ceph_get_snapdir(struct inode *parent)
>>>    	inode->i_atime = parent->i_atime;
>>>    	inode->i_op = &ceph_snapdir_iops;
>>>    	inode->i_fop = &ceph_snapdir_fops;
>>> -	ci->i_snap_caps = CEPH_CAP_PIN; /* so we can open */
>>> -	ci->i_rbytes = 0;
>>>    	ci->i_btime = ceph_inode(parent)->i_btime;
>>> +	ci->i_rbytes = 0;
>>>    
>>>
>>>
>>>
>> Hi Jeff,
>>
>> BTW, why we need to set other members here if the i_state is not I_NEW ?
>>
>> Are they necessary ?
>>
> I think so, at least for most of them.
>
> IIUC, we want the .snap directory's metadata to mirror that of the
> parent directory, so we want stuff like the ownership and mtime to track
> changes in the parent.
Okay.
> I can move the setting of i_op and i_fop into the if block though. Those
> should never change anyway, though setting them is harmless here since
> we're checking to make sure the type is correct above.
>
> I'll go ahead and do that, but I won't bother re-posting the v2 patch
> since it's a trivial change.

Yeah, make sense :-)

Thanks


>
>>> -	if (inode->i_state & I_NEW)
>>> +	if (inode->i_state & I_NEW) {
>>> +		ci->i_snap_caps = CEPH_CAP_PIN; /* so we can open */
>>>    		unlock_new_inode(inode);
>>> +	}
>>>    
>>>
>>>
>>>
>>>    	return inode;
>>>    }
>>