rapid clustered nfs server failover and hung clients -- how best to close the sockets?

[J. Bruce Fields]

On Mon, Jun 09, 2008 at 10:31:37AM -0400, Jeff Layton wrote:
> I can think of 3 ways to fix this:
> 
> 1) Add something like the recently added "unlock_ip" interface that
> was added for NLM. Maybe a "close_ip" that allows us to close all
> nfsd sockets connected to a given local IP address. So clustering
> software could do something like:
> 
>     # echo 10.20.30.40 > /proc/fs/nfsd/close_ip
> 
> ...and make sure that all of the sockets are closed.
> 
> 2) just use the same "unlock_ip" interface and just have it also
> close sockets in addition to dropping locks.
> 
> 3) have an nfsd close all non-listening connections when it gets a
> certain signal (maybe SIGUSR1 or something). Connections on a
> sockets that aren't failing over should just get a RST and would
> reopen their connections.
> 
> ...my preference would probably be approach #1.

What do you see as the advantage of #1 over #2?  Are there cases where
someone would want to drop locks but not also close connections (or
vice-versa)?

--b.