 - Hold a reference from the time vfs_busy starts until vfs_unbusy is    called.  - vfs_getvfs has to return a reference to prevent the returned mountpoint    from changing identities.  - Release references acquired via vfs_getvfs.
 - Hold a reference from the time vfs_busy starts until vfs_unbusy is
   called.
 - vfs_getvfs has to return a reference to prevent the returned mountpoint
   from changing identities.
 - Release references acquired via vfs_getvfs.

Discussed with:	tegge
Tested by:	kris
Sponsored by:	Isilon Systems, Inc.

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