Naive question about grant/map

[Jonathan S. Shapiro]

I have a note about mappings and address spaces pending, but before I
send it I want to ask a naive question about the map operations:

Consider a sequence of operations in which 

	A maps to B
	B maps same stuff to C.

Is there some variant of the 'map' operation in which B does NOT retain
the ability to revoke C's mapping? That is, in which the resulting
mapping dependency hierarchy is

       A
      / \
     B   C

instead of

       A
       |
       B
       |
       C

That is, is there a way for a sender to give a receiver rights on data
that are co-equal in all respects with those of the sender?

If not, is it important?

If such a "coequal map" operation existed, how often would it be used in
contrast to the current map operation?

shap
-- 
Jonathan S. Shapiro <shap at eros-os.org>