Implemented a protocol between a client and its pager to
request and get a capability to ipc to another client of the pager.
Pager first ensures the request is valid from its client.
It then tries to use a greater capability that it possesses, to
produce a new capability that the client requested. Once the kernel
validates the correct one and replicates/reduces it to client's
need, it grants it to the client.
Pager handles client capability requests by using one of its own
capabilities to create a new one that suits the client's needs.
The current issue is that the kernel can have multiple caps and it
may not know which one is suitable for using to create one for the client.
The kernel knows this very well, so the solution would be to attempt to
use capabilities that roughly match (i.e. by type) and leave it to
the kernel to decide whether it is any powerful to suit client's needs.
In posix, test0 makes inter-space ipc for testing extended ipc. This
correctly fails when only the cap to ipc to pager is given to all tasks
in the container.
In order to overcome this problem, the tasks who fork for doing ipc to
each other make a request to the pager to get capabilities to do so.
Pager finds its own widened ipc capability over the container, replicates
it, validates and reduces it to desired boundaries (i.e. just ipc betw.
two spaces) and grants it as IMMUTABLE to requesting tasks.
This protocol may be useful in implementing a client/server capability
request relationship. Code builds but untested.
