/*
* layerfs_snapshot - handle a snapshot through a layered file system
*
* At present, we do NOT support snapshotting through a layered file
* system as the ffs implementation changes v_vnlock of the snapshot
* vnodes to point to one common lock. As there is no way for us to
* absolutely pass this change up the stack, a layered file system
* would end up referencing the wrong lock.
*
* This routine serves as a central resource for this behavior; all
* layered file systems don't need to worry about the above. Also, if
* things get fixed, all layers get the benefit.
*/