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

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

I am investigating the problem of supporting a samba server's granting
of OpLocks to its clients when the files that the samba serving is
accessing are in a clustered file system.

A samba server running in linux determines whether and what kind of
OpLock (i.e. either shared or exclusive) to grant to its clients for a
particular file, by establishing a corresponding lease on the file in
question.  This works well for single host based file systems (e.g.
ext3, etc.) but does not work at all for distributed or clustered file
systems.  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.

I would like to know if there has been any work done in this area and
if so, are there people with whom I could correspond to help me work
this out.

I am fairly new to this area and would appreciate any help that I can get.

Thanks.

- Robert Rappaport