Re: Locking issue between NFSv4 and SMB client

[Trond Myklebust <trondmy@hammerspace.com>]

On Fri, 2021-09-24 at 05:46 +0200, Ralph Boehme wrote:
> Am 24.09.21 um 05:35 schrieb Trond Myklebust:
> > Not if you set the "kernel oplocks" parameter in the smb.conf file.
> > We
> > just added support for this in the Linux 5.14 kernel NFSv4 client.
> > 
> > Now that said, "kernel oplocks" will currently only support basic
> > level
> > I oplocks, and cannot support level II or leases. According to the
> > smb.conf manpage, this is due to some incompleteness in the current
> > VFS
> > lease implementation.
> > 
> > I'd love to get some more info from the Samba team about what is
> > missing from the kernel lease implementation that prevents us from
> > implementing these more advanced oplock/lease features. From the
> > description in Microsoft's docs, I'm pretty sure that NFSv4
> > delegations
> > should be able to provide all the guarantees that are required.
> 
> leases can be shared among file handles. When someone requests a
> lease 
> he passes a cookie. Then when he opens the same file with the same 
> cookie the lease is not broken.

Right, but that is easily solved in user space by having the cookie act
as a key that references the file descriptor that holds the lease. This
is how we typically implement NFSv4 delegations as well.

> 
> Maybe others can comment on the level II oplock problem. Afaik this
> was 
> more a lack of testing.

That would really be a bit of a shame, since the use of leases on top
of networked or clustered filesystems could help speed up state
management operations by avoiding the need for a separate distributed
lock manager.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com