On Fri, 2017-05-12 at 10:34 -0400, J. Bruce Fields wrote: > On Fri, May 12, 2017 at 09:27:21AM -0400, Stefan Hajnoczi wrote: > > Hi, > > I've been working on NFS over the AF_VSOCK transport > > (https://www.spinics.net/lists/linux-nfs/msg60292.html). AF_VSOCK > > resets established network connections when the virtual machine is > > migrated to a new host. > > > > The NFS client expects file handles and other state to remain valid > > upon > > reconnecting. This is not the case after VM live migration since > > the > > new host does not have the NFS server state from the old host. > > > > Volatile file handles have been suggested as a way to reflect that > > state > > does not persist across reconnect, but the Linux NFS client does > > not > > support volatile file handles. > > That's unlikely to change; the protocol allows the server to > advertise > volatile filehandles, but doesn't really give any tools to implement > them reliably. > > > I saw NFS 4.1 has a way for a new server running with the same > > network > > address of an old server to communicate that it is indeed a new > > server > > instance. If the server owner/scope in the EXCHANGE_ID response > > does > > not match the previous server's values then the server is a new > > instance. > > > > The implications of encountering a new server owner/scope upon > > reconnect > > aren't clear to me and I'm not sure to what extent the Linux > > implementation handles this case. Can anyone explain what happens > > if > > the NFS client finds a new server owner/scope after reconnecting? > > I haven't tested it, but if it reconnects to the same IP address and > finds out it's no longer talking to the same server, I think the only > correct thing it could do would be to just fail all further access. > > There's no easy solution. > > To migrate between NFS servers you need some sort of clustered NFS > service with shared storage. We can't currently support concurrent > access to shared storage from multiple NFS servers, so all that's > possible active/passive failover. Also, people that set that up > normally depend on a floating IP address--I'm not sure if there's an > equivalent for VSOCK. > Actually, this might be a use case for re-exporting NFS. If the host could re-export a NFS mount to the guests, then you don't necessarily need a clustered filesystem. OTOH, this would not solve the problem of migrating locks, which is not really easy to support in the current state model for NFSv4.x. > -- Trond Myklebust Linux NFS client maintainer, PrimaryData trond.myklebust@xxxxxxxxxxxxxxx ��.n��������+%������w��{.n�����{��w��� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
