Re: whither NFS umount?

["J. Bruce Fields" <bfields@fieldses.org>]

On Thu, Oct 14, 2010 at 10:17:21AM -0400, Trond Myklebust wrote:
> On Thu, 2010-10-14 at 10:00 -0400, J. Bruce Fields wrote:
> > So, on the server side...  As Trond says, we'd like to know which
> > clients have been active recently.  (In the v4 case, the lease gives
> > that a precise meaning.  In the v2/v3 case, I suppose we just pick a
> > number to use as a timeout.  We could use the v4 lease time.)  It's only
> > the kernel that knows which clients have been active recently.  So we'd
> > need a way for the client to export that information to userspace.
> > 
> > Greg's per-client statistics might be a good starting point:
> > 
> > 	http://thread.gmane.org/gmane.linux.nfs/25537/focus=25534
> > 
> > Though that's just per-ip address, which isn't ideal for v4.  (In the v4
> > case the client identifier/owner allows us to distinguish e.g. between
> > multiple clients on the same machine, or behind the same NAT.)  I think
> > that wouldn't be hard to fix.  (Maybe just add on some ascii-escaped
> > representation of the clientid to the end of the same line?)
> 
> Relying on the lease isn't good enough. While an NFSv4.1 client is
> indeed required to renew its lease before it can do any useful work, an
> NFSv4.0 client is only required to establish a lease in order to OPEN a
> file.
> The Linux NFS client will, for instance, defer establishing a lease
> until first open, and will stop renewing that lease when nobody is
> holding any open file state.

Good point, thanks.

--b.

> One alternative to using the lease state is to use the TCP connection
> state and/or the TCP/UDP port number. That's pretty much what we use to
> distinguish separate NFS clients in the replay cache anyway...