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Re: emulating no-senders notifications in L4?

From: Debian UserAd Buijsen
Subject: Re: emulating no-senders notifications in L4?
Date: Fri, 21 Dec 2001 15:09:54 +0100 (CET)

>> I think here the answer has to be no.  BTW, one interesting question for L4
>> is:  How do you prevent that a task sends its own, faked messages to the
>> server, circumventing the port right server.  In other words, how do you
>> enforce the port server.  This might involve some more RPCs the server has
>> to do with the port server.

The next version of L4 will probably support IPC redirection, using an 
in-kernel table of
sources and destinations.  A 'privileged' task in user space will set this 
table, thus controlling 
whether entity A can send (directly) to entity B or not; in the latter case the 
IPC will typically be
redirected to another entity.  A 'one-shot' flag in the redirection table would 
make it easy to
emulate send-once rights.  The privileged task mentioned above could hand out 
the port rights
and should do enough bookkeeping to clear up after tasks that have terminated 
graciously or

In case you are wondering why I used the term 'entity' in stead of threads: 
reading of the L4 list
at Karlsruhe suggests that the semantics of tasks and threads will change as 
well.  I really don't
think we can do anything fundamental about L4-hurd until the specs of L4V4 are 

 Ad Buijsen

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