Naive question about grant/map

[Jean Wolter]

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

> 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? 

I am not sure whether I understood the question correctly but there is
the grant operation. 

After A maps to B and B maps to C it would look like 

        A -> B -> C

in contrast to A maps to B and B grants to C which would look like

        A -> C

> That is, in which the resulting mapping dependency hierarchy is
> 
>        A
>       / \
>      B   C

This graph would be a result of the following operations

        A maps to B
        A maps to B and B grants to C

There is no single operation which could be used as a replacement for
the map/grant sequence.

> 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?

No, there ist only grant, where the sender transfers its own rights to
the receiver and has no access to the page afterwards.

> If not, is it important?

I don't know. So far the map/grant combination was enough to handle
all scenarios. Do you have a scenario in mind where such an operation
would be useful?

Regards,
Jean