Comparing IPC and capability invocation

Hermann Härtig haertig at
Mon Dec 22 11:10:26 CET 2003

Jonathan S. Shapiro wrote:
> This is a response to several messages (from Volkmar, Rudy, Hermann) at
> once. The delay has partly been due to other demands on my time, and
> partly because I wanted to consider how to answer.

It seems to me (but this needs to be confirmed in face to face 
discussions in January, I am now confused about the many "id"s)
that both, EROS and the "Generalized Mappings" proposal,
replace (in relation to original L4) thread-id by some other
"id" as an unforgable part of messages. The "other id" is
protected by the kernel and managed by user level processes.
In EROS, it is managed by the server, in "Generalized
Mappings" by the pager providing the mappings.
In "Generalized Mapping", the size of this "id" is under
user control as well. Thus no problem with register payload,
the "id" can become even smaller than the original thread-id in specific 
cases. In EROS, these "id"s are under complete control of the process
providing a service, in L4 "Generalized Mapping" the pagers can restrict 
the "id" spaces of their clients in a pager hierarchy.

I do not understand the relation of this "id" to "user-level object 
invocation" as a first class EROS citizen.

Merry Chrismas to all of you


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