[AFS3-std] Locking, ACL's, and Capabilities

[Jeffrey Altman]

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At the AFS Hackathon there was an active discussion of these issues.
Here is a summary of what was concluded:

(1) The file server will advertise a capability flag indicating that
    write-lock access is controlled by the same access rules as
    writing to the files.  ('w' or 'i' bits)

(2) It was agreed that the desired granularity for advertising the
    locking sanity of ACLs is at the directory level.  This sanity
    value will be communicated by the file server to the cache
    manager within a future revision to the FetchStatus RPC data
    structure. The sanity value will indicate that the 'k' bit is
    intentionally set or not set with knowledge of the implications for
    applications which require the ability to obtain a read-lock before
    the file can be opened for reading or executing.

    It was also agreed that it is inappropriate to revise the
    FetchStatus RPC just for the locking sanity value.  In the meantime,
    the file servers will support a runtime switch which will cause
    a capability flag to be set indicating that the ACLs on all served
    directories are sane.  This is intended to be used by sites that
    have always applied sane ACLs.

(3) The Windows clients will support the following locally controlled
    locking policies:

 (3a) [default]
      Never obtain locks if the volume is RO.
      Obtain locks if the volume is RW and ignore read-lock access
      denied errors if the user's rights are no better than 'rl' and the
      ACLs are not sane.

 (3b) Never obtain read or write locks.  (In other words, support the
      old Windows AFS client behavior.)

 (3c) Never obtain locks if the volume is RO and always treat the ACLs
      as sane.

(4) The file server will implement a revised SetLock RPC which supports
  (4a)  Non-blocking lock upgrades from read-lock to write-lock
  (4b)  Lock downgrades from write-lock to read-lock
  (4c)  Will not utilizes error codes in ambiguous ways.

(5) The client ExtendLock behavior should be altered to pay attention to
    EINVAL errors when renewing lock lifetimes.  On Windows, the clients
    will following the CIFS behavior and invalidate the file handles.
    On Unix clients, the clients will stop attempting to extend the
    lock.  However, on Unix there is no error that can be returned to
    the application.

(6) In order to support more intelligent lock handling, the file server
    needs to track which client the lock was issued to.

Jeffrey Altman (on behalf of the hackathon attendees)




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