Re: [PATCH] VFS: Unlink should revoke all outstanding leases on file

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, May 19, 2010 at 05:46:23PM +0800, Mi Jinlong wrote:
> 
> 
> J. Bruce Fields :
> > On Fri, May 14, 2010 at 02:31:12PM -0400, Trond Myklebust wrote:
> >> On Fri, 2010-05-14 at 13:59 -0400, Trond Myklebust wrote: 
> >>> Note that the server should also recall the delegation if someone
> >>> attempts to violate the guarantees that are listed in section 9.4: Open
> >>> Delegation
> >>>
> >>>    When a client has a read open delegation, it may not make any changes
> >>>    to the contents or attributes of the file but it is assured that no
> >>>    other client may do so.  When a client has a write open delegation,
> >>>    it may modify the file data since no other client will be accessing
> >>>    the file's data.  The client holding a write delegation may only
> >>>    affect file attributes which are intimately connected with the file
> >>>    data:  size, time_modify, change.
> >>>
> >>> IOW: even if you hold a write delegation you are not allowed to change
> >>> the file mode bits, owner, group or acls...
> >> ...or the nlink value. So technically, we should also recall the
> >> delegation when someone creates or deletes a hard link. I think I need
> >> to remind Tom that he should add that to the RFC3530bis draft...
> > 
> > Yep.  And fixing all these cases is required before our the server's
> > NFSv4 server is ready for much of anything.
> > 
> > I'm not sure ading break_lease() to may_delete() is right, but maybe
> > it's better than nothing.
> 
>   Agree with you.
> 
> > 
> > One problem is that there's a race: nothing I can see stops anyone from
> > getting another lease after may_delete() but before the delete happens.
> 
>   Yes. 
>   The problem will exist, but there isn't some better methods to avoid it.
>   Is there a lease lock exist in kernel? 
>   If that's true, the problem will be fixed simply.

I don't know of any existing lock that does exactly what we want.

Somebody at citi worked on a better lease implementation for a while,
but I don't think we ever really got it right; the last version I can
find is here:

	git://linux-nfs.org/~bfields/linux-topics.git leases

--b.