Re: File system awareness (or lack thereof) of vfs granting of leases

["Robert Rappaport" <robert.rappaport@gmail.com>]

On 2/18/07, J. Bruce Fields <bfields@fieldses.org> wrote:
> On Sat, Feb 17, 2007 at 12:32:42AM -0500, Wendy Cheng wrote:
> > Robert Rappaport wrote:
> >
> > >[snip]
> > >....   This is because the vfs running on the same node where the
> > >samba server is running is not necessarily aware of all accesses to
> > >the file on which it is granting a lease.  Since vfs does not
> > >currently inform file systems about the granting and rescinding of
> > >leases, a clustered file system cannot allow a samba server to support
> > >OpLocks on its files and this has a negative impact on performance.
> > >
> > >What I think is needed is to add a file systems defined
> > >file_operations function, that would be invoked when vfs is
> > >considering the granting of a lease on a file associated with an
> > >inode.  Such an enhancement would allow a file system to be come aware
> > >of vfs lease activity and allow it to support this activity.
> > >
> > NFS has similar issues because Linux NLM-VFS does not invoke server side
> > filesystem specific lock method. This implies NFS client applications is
> > not able to use posix locks to coordinate file access across different
> > nodes  with a cluster filesystem, even the cluster filesystem itself
> > does support posix locking.
>
> We also have the same problem with leases, since we're using leases to
> implement NFSv4 delegations.  There's a simple-minded patch here:
>
>         http://linux-nfs.org/cgi-bin/gitweb.cgi?p=bfields-2.6.git;a=commitdiff;h=4e8aff5dabe07b2e4e95ef0c741a34f65409087f
>
> I'm not really sure if it's right.
>
> --b.
>

Thank you both for your helpful replies.  In particular, the addition
of the calls to file system specific functions in routines,
fcntl_setlease() and break_lease(), as well as the modifications to
the file_operations and inode_operations structures, pointed to by
Bruce's reply, look exactly like the hooks that I would need to
proceed to resolve my problems.  Is there any timetable established
for these modifications to make it into a future release?  These hooks
would clearly benefit any cluster file system that has to deal with
leases.

- Robert Rappaport