Re: [PATCH 17/18] xfs: implement pnfs export operations

[Dave Chinner <david@xxxxxxxxxxxxx>]

On Fri, Jan 09, 2015 at 12:41:59PM +0100, Christoph Hellwig wrote:
> On Fri, Jan 09, 2015 at 08:04:05AM +1100, Dave Chinner wrote:
> > > If the client sends the opaqueue device ID that contains the generation
> > > after the grow to a server that had crashed / restarted the server
> > > will reject it as the server starts at zero.  The causes the client
> > > to get a new, valid device ID from the server.
> > 
> > But if the server fs has a generation number of zero when it
> > crashes, how does the client tell that it needs a new device ID from
> > the server?
> >
> > > Unlike the NFS file hadles which are persistent the device IDs are 
> > > volatile
> > > handles that can go away (and have really horrible life time rules..).
> > 
> > Right. How the clients detect that "going away" when the device
> > generation is zero both before and after a server crash is the
> > question I'm asking....
> 
> The server tells the client by rejecting the operation using the
> device ID.

Ok, so:

client                          server

get layout
dev id == 0
                                grow
                                gen++ (=1)
                                crash
                                ....
                                gen = 0 (initialised after boot)

commit layout
dev id == 0
                                server executes op, even though
                                device has changed....

What prevents this? Shouldn't the server be rejecting the commit
layout operation as there was a grow operation between the client
operations?

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx