Restarting exports disturbs clients

[Daniel Feenberg]

When we change the exportfs file on our FreeBSD 9.1 fileserver:

   kill -HUP `cat /var/run/mountd.pid`

it kills the jobs on  clients that have files open on the fileserver.
This is pretty inconvenient for users (and us). Is there a way around 
this? We have noticed that a Linux fileserver can restart nfs without 
distrubing clients (other than a short pause). The Linux restart
doesn't restart the locking mechanism - is that the difference? We
could do without locks, even without NFSv4, for that matter, if it
would let us change exports without disturbing users. Perhaps there
there is an NFS shutdown procedure that we should be using?

Daniel Feenberg
NBER