PATCH [0/7] Fix posix locking code

[Trond Myklebust]

The following patches fix up a number of inconsistencies within
the current VFS locking code.

The main problems addressed are

  - Inconsistent definition of what the lock owner means.
  	Currently, the VFS code is sometimes using current->files,
	sometimes current->tgid, and sometimes a combination of both.
    It turns out that CLONE_FILES more or less forces us to use
    current->files as the basis for the lock owner (or bad things
    will happen) so we must drop the checks for current->tgid.
  - Design worries: separate out callbacks used by lock managers,
    such as lockd, and those used by filesystems.
  - posix_lock_file() is called by the VFS *AFTER* the filesystem
    has been notified. However because it uses no locking, and
    may even sleep, there are serious race issues.
    By moving the posix_lock_file() call into the filesystem
    callback, the filesystem may implement its own locking scheme
    to avoid trouble.

Cheers,
  Trond

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