Re: [Gluster-devel] What functionality is expected from persistent NFS-client tracking?

[J. Bruce Fields]

On Wed, Feb 06, 2013 at 06:19:56PM +0100, Niels de Vos wrote:
> On Thu, Jan 31, 2013 at 03:19:28PM -0500, J. Bruce Fields wrote:
> > On Thu, Jan 31, 2013 at 10:20:27AM +0100, Niels de Vos wrote:
> > > Well, the NFS-server dynamically gets exports (GlusterFS volumes) added 
> > > when these are started or newly created. There is no hard requirement 
> > > that a specific volume is available for the NFS-server to place a shared 
> > > files with a list of NFS-clients.
> > 
> > I'm not sure what you mean by "there is not hard requirement ...".
> > 
> > Surely it's a requirement that an NFS server have available at startup,
> > at a minimum:
> > 
> >     - all exported volumes
> >     - whichever volume contains /var/lib/nfs/statd/, if that's on
> >       glusterfs.
> > 
> > otherwise reboot recovery won't work.  (And failover definitely won't
> > work.)
> 
> Well, with the current state of things, the GlusterFS NFS-server (gNFS) 
> does not enforce that there are any volumes available to export. These 
> can be added dynamically (similar to calling exportfs for Linux nfsd).  

Sure, it's fine to allow that, just as long we make sure that anything
already exported is available before server start.

> When an NFS-client tries to mount an export immediately after gNFS has 
> been started, the MOUNT will return ENOENT :-/

It's not new mounts that are the problem, it's preexisting mounts after
a server reboot:

An application already has a file open.  The server reboots, and as soon
as it's back up the client sends an operation using that filehandle.  If
the server fails to recognize the filehandle and returns ESTALE, that
ESTALE gets returned to the application--definitely a bug.

So for correct reboot recovery support, any export in use on the
previous boot has to be back up before the NFS server starts listening
for rpc's.

(Alternatively the server could look at the filehandle, recognize that
it's for a volume that hasn't come up yet, and return EJUKEBOX.  I don't
think gluster does that.)

--b.