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Re: emulating no-senders notifications in L4?

From: Niels Möller
Subject: Re: emulating no-senders notifications in L4?
Date: 20 Dec 2001 17:28:33 +0100
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.1

"Yoshinori K. Okuji" <okuji@kuicr.kyoto-u.ac.jp> writes:

> > Can the scheme above be improved (without adding security features
> > like port-rigts to the kernel)?
> If most RPCs are normal messages from a task having a send right to
> one having a receive right, it might improve the performance to map
> the arrays to every task in read-only mode, so that it can check if an
> IPC is valid by itself.

Interesting idea! You can do this, and still have the port-rights
server send no-senders notifications when send-rights are removed
from the table.

> This isn't good for "send once" rights, but I don't think "send
> once" rights are used so often.

Then the receiving task would have to tell the port-rights server that
the send-once right is consumed and should be deleted. I'm not sure if
a receive right in general implies the right to selectively revoke
send rights. And one also gets a few race conditions to deal with. It
might not be worth the trouble. 

> However, I'm not sure if L4-Hurd needs a central port right server. Is
> it really necessary?

My reasoning, in

  Message-ID: <nnelmybwbf.fsf@sture.lysator.liu.se>
  Date: 16 Nov 2001 15:54:28 +0100)

was that an extra level of indirection is necessary for implementing a
reliable no-senders notification. I'd be delighted to be proved wrong.


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