[linux-cifs-client] Re: lookup intent patch

[Shirish Pargaonkar]

On Mon, Mar 30, 2009 at 12:45 PM, Jeff Layton <jlayton at redhat.com> wrote:
> On Mon, 30 Mar 2009 10:57:32 -0500
> Shirish Pargaonkar <shirishpargaonkar at gmail.com> wrote:
>>
>> Jeff,
>>
>> Thanks.  Looking into it. I am trying to figure out the need/necessity
>> for cifs_lookup to call lookup_instanitate_flip.
>> lookup_instantiate_filp does call dentry_open and if cifs_lookup does
>> not call lookup_instantiate_flip,
>> nameidata_to_filp will call dentry_open.
>> So I am not sure what we loose if dentry_open does not get called
>> between lookup_hash and nameidata_to_flip
>> because of an error between those two calls, specifically how will the
>> cause of open file getting closed on the
>> server will be served if there was an in-betwen error by calling
>> lookup_instantiate_filp.
>>
>
> I'm not certain since I haven't tested your patch, but you may end up
> with an inode refcount leak (aka Busy inodes after umount...). You're
> doing an open on the file in the lookup and I think that increases the
> refcount of the inode (i_count). Eventually, that inode gets "put" when
> you close the file. In the error situation described above though, that
> put will never occur. As far as the VFS is concerned, the file was
> never actually opened, so it doesn't need to issue a fput().

We would still be in do_flip_open and so if there is an error, while exiting
release_open_intent would get called which would so the cleanup i.e.
call fput().
Let me introduce an error in between to verify whether the data structures
are cleaned up, such as i_count of an inode.

>
> Properly cleaning up the references is the main reason to make sure
> that you pass the filp back to the caller here. Closing the open file
> on the server is also a nice side benefit since that could block the
> granting of oplocks and such.
>

I think caller is oblivious to the speed-up mechanism that cifs is attempting
by taking advantage of lookup intents to reduce network traffic.

> --
> Jeff Layton <jlayton at redhat.com>
>