[nfsv4] "Courtesy locks"

[<[e-mail]>]

The term "courtesy locks" is Trond's.  It refers to the practice of
allowing locks associated with an expired lease to remain around, "as a
courtesy to the client or as an optimization" (see section 8.6.3 or RFC
3530).  The text that is associated with this situation is not as clear
or complete as it should be and a number of RFC3530bis issues are
related to it.

In deciding how to address this, we need to find out what exactly
clients and servers do.  A long while back I promised to send mail and
gather up the requisite information, and now my promise has caught up
with me.  If you can answer the following questions via email that would
be great.  If not, I hope people will at least find out what their
implementations do on these points so we discuss it at the upcoming
bakeathon.

This looks pretty daunting but most people will probably say "Yes" to
(S1) and/or easily deal with (C1), (C2), and (C3).

Make sure you use black pen and completely fill in the circles :-) 


If you have a client and not a server, skip to (C1)

S1) When a lease expires, do you simply release all
    the associated locks?

    If so, go to (C1), or if you don't have a client you 
    are all done.

S2) If you do maintain locks for a longer time, when and if
    there is a conflict before the lease being reactivated,
    what do you do?

    A) Release all the locks associated with that client
    B) Release all the locks held by that client for that 
       same fh.
    C) Something more limited than (B) that includes the lock
       that had the conflict.

    If you answered (A) or (B), skip down to (S7).

S3) If the lock that had a conflict is a byte-range lock,

    S3.1) Is the associated open released as well?
    S3.2) Are all byte-range locks associated with the
          same open released as well?
    S3.3) Are all byte range locks associated with the same
          client/lock-owner released as well?
    S3.4) Are all byte-range locks associated with the 
          same open and owned by the client/lock-owner
          released as well?
    S3.5) If the lock is associated with an open that is
          subordinate to a delegation, is the delegation
          released as well?
    S3.6) Are there any other locks that are released?

S4) If the lock that had a conflict is an open?

    S4.1) Are byte-range locks associated with this open
          released as well?
    S4.2) If the open is associated with a delegation,
          is the delegation released as well.

S5) If the lock that had the conflict a delegation?

    S5.1) Are opens associated with that delegation
          released as well?
    S5.2) Are all opens for that client and for that fh
          released as well?
    S5.3) Are all byte-range locks associated with open
          that are associated with that delegation released
          as well.
    S5.4) Are all byte-range locks for that client and for
          released as well?

S6) Are there any other situations in which release of a 
    lock due to a conflict will cause other locks to be
    released?

S7) After releasing locks due to a conflict, what happen if
    the associated stateid is referenced, assuming that 
    happens relatively quickly?

    S7.1) The client gets NFS4ERR_EXPIRED?
    S7.2) The client gets some other error?  What?
    S7.3) Can it be different for different types of stateids?

S8) Assuming that the release does not cause immediate freeing
    of the stateid (and returning NFS4ERR_BAD_STATEID), what 
    provision is made for eventual deletion of such stateids?

    a) There is an LRU mechanism to eventually delete them.
    b) They are kept around until the client or server 
       reboots.
    c) It depends on the type of lock.

If you have no client, you are done.

C1) When you get NFS4ERR_EXPIRED, what happens?

    a) Assume all locks associated with lease have been released
       that the client needs to create a new clientid?
    b) Assume that it means one or more locks have been lost and
       the client needs to determine what as gone and which are
       still valid.
    c) Something else.  What?

C2) If you didn't answer (a) to (C1), are there any assumptions
    (of the sort mentioned in (S3) to (S6)) whose violation would
    cause problems? 

C3) How do you respond to getting the following errors?  Specifically
    would it be problematic if that error were returned when a
    courtesy lock was released due to a conflict:

    C3.1) NFS4ERR_ADMIN_REVOKED
    C3.2) NFS4ERR_BAD_STATEID