NAME
        DupLockFromFH -- Gets a lock on an open file (V36)

   SYNOPSIS
        lock = DupLockFromFH(fh)
        D0                   D1

        bptr duplockfromfh(bptr)

   FUNCTION
        Obtain a lock on the object associated with fh.  Only works if the
        file was opened using a non-exclusive mode.  Other restrictions may be
        placed on success by the filesystem.

   INPUTS
        fh   - Opened file for which to obtain the lock

   RESULT
        lock - Obtained lock or NULL for failure

   SEE ALSO
        duplock(), lock(), unlock()