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

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

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.