Deceiving IPC question: Bug or Feature?

[gernot at cse.unsw.edu.au]

We have noticed the following re deceiving IPC in L4/MIPS.

Assume task A is the chief of task B, which is the chief of task C. aa
is a thread in A, bb a thread in B, cc a thread in C.

aa does a closed receive from bb. bb sends a deceiving message to aa
with cc as the virtual sender. aa receives the message (although the
virtual sender is different from the source specified in the
receive). The kernel returns to aa the virtual sender specified by bb
(i.e., cc), but the C bindings discard this information, so aa cannot
see it using the C interface.

If in the otherwise identical situation aa does a closed receive from cc
it does NOT receive the message.

My questions:

 - do all L4 versions show this behaviour?

 - is this the correct behaviour?

Gernot
--
Gernot Heiser                ,--_|\   School of Computer Sci. & Engin.
Phone:  +61 2 9385 5156     /      \  The University of NSW
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E-mail: G.Heiser at unsw.edu.au      v   http://www.cse.unsw.edu.au/~gernot
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