Re: [nfsv4] 3530bis Issue 39: Clarification on renewing sequence IDs

[Trond Myklebust <[e-mail]>]

On Thu, 2010-11-04 at 15:57 -0600, Robert Thurlow wrote:
> Robert Thurlow wrote:
> > Hi folks,
> > 
> > This is issue 39 from 
> > http://github.com/loghyr/3530bis/blob/master/tasklist.txt.
> > 
> > In implementing NFSv4 migration support, we believe that
> > MOVED and LEASE_MOVED need to be added to the list of errors
> > in 8.1.5 which do NOT result in incrementing the open owner
> > or lock owner sequence ID.  The goal is to make the sequence
> > ID readily calculable for both the client and the destination
> > server after the migration has occurred.
> > 
> > On the 3530bis call, this appeared exactly backwards to some
> > others - that since a completely gross error had not occurred,
> > we should increment the sequence ID and the client and the
> > destination server should know to expect that when they interact
> > after a migration.  I do not know this issue well enough to
> > properly defend a position, so please reply with your reasoned
> > opinion :-)
> 
> I don't think this has had a response.  If you disagree with
> the wording change, now is the time to say so.

As stated on the confcall, I strongly disagree with this change w.r.t.
NFS4ERR_LEASE_MOVED. The operation that resulted in a
NFS4ERR_LEASE_MOVED cannot be safely replayed if the sequence id has not
been bumped.

The point is that NFS4ERR_LEASE_MOVED is an error that depends on the
state of a _different_ filesystem. It does not even pertain to the
actual state you are trying to modify (and is a monstrous hack). Worse
yet, that error condition can be cleared at any time with no
consequences for the stateids held by the client, so unlike
NFS4ERR_BAD_STATEID or NFS4ERR_BAD_SEQID, there is no ordering w.r.t.
the operation that you are retrying.

IOW: if the error condition happens to get cleared between two replays
of the operation, the client may end up getting 2 conflicting replies
(one NFS4ERR_LEASE_MOVED, the other being a change of state on the
server). Which one does it choose?

So how about counter-proposal: we bury NFS4ERR_LEASE_MOVED at a
cross-roads with a stake through its heart, and promise never to mention
it again except when the kids need scaring to bed...

Trond