Re: Subsystem booting

[Niels Möller]

Marcus Brinkmann <address@hidden> writes:

> On Sun, May 25, 2003 at 12:17:36PM +0200, Niels Möller wrote:
> > What should the subsystem boot procedure be like? Is the following
> > close to right?
> > 
> > For each subsystem, there's one "subsystem-root" module. These are
> > loaded by grub, after the rootserver.
> 
> No, there can be several modules per subsystem.  In fact, I am not sure I
> want to worry about subsystems at all at this stage, but an argument in the
> grub module command line can specify the subsystem.

Sure, but for each subsystem there will only be one task (or rather, a
small number of threads) which the rootserver consideres privileged.
It seems simpler if that corresponds to one grub module, but you're
right that's not absolutely necessary.

BTW, I spent the afternoon rereading the L4 spec. Section 7.7 says
that the kernel can start three special tasks: sigma0, sigma1, and the
root server. The current kickstart.cc never loads any sigma1, and the
spec doesn't say much more about it. So what is sigma1 supposed to do?

> About that.  Did you check out Neals l4hurd code?

No, I guess I should. Where exactly can I find that? I browsed the
l4hurd project at savannah, but didn't find anything there that's
obviously written by Neal.

> > For the hurd, the task server needs another grub module for the first
> > task(s), which could be something like serverboot (processing
> > additional GRUB modules),
> 
> Serverboot is dead, man.

;-) The serverboot configuration etc is dead. But some task has to get
the grub modules needed for booting, and get some tasks running and
interconnected. Who's going to do that? Not the L4 kernel, not the
root server, probably not the task server either.

> > The root server could also support have some ipc call for starting a
> > new subsystem, later than boot time.
> 
> Not at all.

I don't remeber exactly how I thought when I wrote that. But perhaps
the right way to get a new subsystem, and start a thread with
privileges with respect to the root server, is to cooperate with the
privileged task in your current subsystem. Some coordination on
subsystem id allocation would be nice, but ok, those are very
secondary issues for the moment.

Regards,
/Niels