Re: emulating no-senders notifications in L4?

[Niels Möller]

Jean Wolter <jean.wolter@inf.tu-dresden.de> writes:

> nisse@lysator.liu.se (Niels Möller) writes:
> 
> > When thinking some more, I realize that you can perhaps distribute the
> > "central" registry, giving the owner of each receive right the
> > reponsibility to keep track of all corresponding the send rights. Is
> > that what you're thinking of? 
> 
> Thats right, that was what Michael and Sven implemented when they did
> a Mach emulation for L3 (the precursor of L4). Michael mentioned it
> some weeks ago and there is a paper on our web sites about it
> (http://os.inf.tu-dresden.de/~hohmuth/dir/pub).

Thanks for explaining this. I guess I should read that paper.

> > Nice idea. A few potential drawbacks is
> > that
> > 
> > 1. Transfer of port-rights gets more complicated. In particular the
> >    transfer of receive rights becomes more difficult. Does the hurd
> >    ever need transfer of receive rights?
> 
> Sure you would have to contact the owner of the port to transfer a
> send right. How often does this happen?

Hmm, I guess most cases port rights that are passed on to other tasks
are newly created ones (happens at open(), for instance, and ports
handed out by the auth server).

> And the main question is: Does Hurd actually use the possibility to
> transfer receive rights?

I'd like to know that too.

> > 2. You get a lot more parties that are interested in task death
> >    events. The task server to keep track of all subscriptions. 
> 
> How many servers are there? How often are tasks created and destroyed
> compared to the number of ipc which would have to go through the port
> server?

Probably not more than manageble.

> > So far, I've been thinking of delegation (i.e. transfer of send
> > rights) as something that is under complete control of whoever wants
> > to give a way a right, [...]

> Is that information hiding a requirement or just nice to have? If it
> is required you need the port server, if not...

It is somewhat subtle change, but I don't think it is terribly
important.

Regards,
/Niels