So another patch set for a Linux Dynamic Pseudo Root has been submitted by Steve Dickson to the Linux NFSv4 mailing list:

The following patch series gives rpc.mountd the ability to allocate a dynamic pseudo root, so the
'fsid=0' export option is no longer required. This allows v2, v3 and v4 clients mounts without
any changes to the server's exports list.

One anomaly of the Linux NFS server is that it requires a pseudo root to be defined. Currently
the only way a pseudo root can be defined is by setting the fsid to zero (i.e. fsid=0). So
if we wanted to make v4 the default mounting version and have things just work like v2/v3 all
of the existing exports configurations would have to change (i.e. a 'fsid=0' would have to
be added) to support a v4 mounts, which, imho, is unacceptable. So this patch series address this problem.

Steve has really highlighted a huge gap in seamless integration of the Linux NFSv4 implementation into automounters, etc. The path to an export should not change based on the version of the protocol.

Hmm, strike that, from a re-reading of I'm not sure if this patch eliminates my concern about the mount path or not. I.e., above he talks about adding a 'fsid=0' on the server and not what the client has to do about the path.

Time to ask him!

Update: Steve says it does address the mount path issue we've seen in the past.

I just got a framework in place for a table driven approach for snoop to decode the Control Protocol used between our DS and MDS servers for pNFS.

Here you can see the DS talking to the MDS and the MDS sending a NULL query:

[th199096@pnfs-9-25 ~]> sudo snoop.ctl -i /root/ds2tmds.snoop | grep CTL
  4   0.00596    pnfs-9-25 -> pnfs-9-26.Central.Sun.COM CTL-DS C DS_EXIBI
  6   0.00000 pnfs-9-26.Central.Sun.COM -> pnfs-9-25    CTL-DS R DS_EXIBI
  8   0.00009    pnfs-9-25 -> pnfs-9-26.Central.Sun.COM CTL-DS C DS_REPORTAVAIL
 13   0.00000 pnfs-9-26.Central.Sun.COM -> pnfs-9-25    CTL-MDS C MDS_NULL
 15   2.99097    pnfs-9-25 -> pnfs-9-26.Central.Sun.COM CTL-MDS R MDS_NULL
 17   0.00012 pnfs-9-26.Central.Sun.COM -> pnfs-9-25    CTL-DS R DS_REPORTAVAIL

Guess I'll have to file in the guts of this to see what is really being said here!