Delegations

• Don't make client's reads conflict with its own delegations:

  Current situation: nfsd_open() calls break_lease() but break_lease has only inode pointer, indication of requested access--no notion of owner identity.

  Requirements:

  • Delegations must conflict with local opens and leases. (No optimizing out break_lease when we know there aren't conflicts with other nfs callers.)

  Possible solutions:

  • Coalesce all delegations held by the server into a single lease, write if possible, otherwise downgraded to read. On break, revoke set of delegations that conflict, downgrade or remove as appropriate. For now (without write delegations implemented), the breaking of a write lease will be a trivial downgrade operation; upgrades may be attempted on subsequent opens if desired.

    NOTE: obstacle to write deleg implementation currently: initial checks for d_count and i_count prevent granting *any* write leases at this point.... FIX!

    If we continue to count on d_count and i_count to identify other writers, then we also need to coalesce nfsd's readers and writers; currently it keeps a struct file per stateid.

    If we kept a single open file for the entire server, would we prevent the filesystem/security subsystem from performing appropriate security checks at open time? *Must* get these sorts of questions about file scope answered:

    • Ask Trond, Christoph, fs-devel....
    • Check filesystem open code, private data, etc.
    • Think about cluster fs case.
  • Pass into setlease the number of references we know we hold. (Make sure that can't be filesystem dependent somehow.)
  • While we're here, see projects/2.5-nfsv4/RESCUED-lease-cleanup

  Question to research: is current self-conflicting semantics correct for file leases?

  • Are leases defined elsewhere (Windows?), and what do they do there?
  • Who uses leases (Samba, ?), and what do they expect of them?
• Adjust # of delegations to give out by available memory?
• Fix delete/rename.
• Measure expense of delegation recall??? Etc.