Re: [9fans] A proposal regarding # in bind

[Martin C.Atkins <martin@mca-ltd.com>]

On Tue, 25 Feb 2003 11:49:59 -0500 Dan Cross <cross@math.psu.edu> wrote:
> > > Newns should only work if /proto is mounted, right? Just like it shouldn't work
> > > after a pctl(NODEVS). Or is newns more powerful than I had appreciated?
> >
> > [RFCNAMEG not RFNAMEG]
> >
> > Newns builds a new name space from scratch.  The implementation
> > is in /sys/src/libauth/newns.c.

Right. I forgot about RFCNAMEG, and assumed that it just read /prog/pid/ns
and unmounted it found there! But...

> > Once newns opens the file describing the name space it is
> > to construct, it clears the name space with rfork(RFCNAMEG)
> > and then starts rebuilding.  If rfork(RFCNAMEG) doesn't clear
> > /ur, then /ur is still a special case.  If it does clear /ur, then
> > how do you get it back?
>
> Hmm.  I wonder if one can post a file descriptor for a kernel
> device under /ur ala what srv does.  Then, newns() could simply
> open that file descriptor, clear the namespace, and then mount
> it.  That's not shockingly different from what we do now.

This sounds neat to me. It's not really a special case any more, just
the application of a general mechanism. (I don't like special cases
either! :-)

> Similarly, the bootstrapping case could be handled by having the
> kernel pass init() an open file descriptor, which it could mount
> on /ur.  I'm not so concerned about being able to remount it in
> a process (or descendent thereof) that's unmounted it, so I see
> little difference between ``bigur'' and ``smallur''.  If you
> want /proc, mount it.  If you want #|, mount it somewhere, then
> do your unmount.  Environment's might be a little wierd to deal
> with, though.

Agreed! That was exactly my point of view too - I only suggested smallur
to show that there are several possible approaches.

>
> 	- Dan C.
>

Re: /ur introducing more special cases than it removes: I believe
that most of the new special cases are to continue the support for
the old '#' syntax. During the transition period, there would of course
be more complications, since both the old and the new syntaxes
have to work simultaneously!

However, once backwards compatibility for '#' could be removed
completely, then using Dan's suggestion, I would have thought the
'/ur' approach would be gloriously free of special cases (except
perhaps, the fact that init is spawned with an open file descriptor).

Anyway, the whole thing was just a suggestion/idea/question, and the
discussion has been educational for me, at least. (It sure beats spam
and "how do we avoid spam" messages, however important the later
might be! :-)

Martin
--
Martin C. Atkins				martin@mca-ltd.com
Mission Critical Applications Ltd, U.K.		http://www.mca-ltd.com