Re: [9front] srv(3) clone and srvid

[unobe@cpan.org]

Quoth ori@eigenstate.org:
> Quoth Jacob Moody <moody@mail.posixcafe.org>:
> > Yes, clone works like how it does in /net, the board is only open for as long
> > as you have the fd open. So you cat'd it which opened it, read the new id, then closed
> > it deallocating the child srv. You need to keep the fd open for the length of time you
> > use the child srv, Or if you wish to 'pin' the child srv you can stash the clone fd itself
> > as a file in the child srv. This will keep the child srv around until you remove the pinned
> > clone fd.

Thank you Moody. I'm still misunderstanding something because I would have that:
	 bind -c '#s20' /srv
when /srv/20 isn't available would have failed somehow, since the man page states:
    As a convention, /lib/namespace
	accepts the path to the service directory from the environ-
	ment variable $srvspec, making it possible to start a new
	namespace using a specific service directory as a starting
	point.

But for comparison, this has no failure either:
	bind '#l20' /net
so I still need to wrap my head around something.

> for an example of how it's used on shithub:
> 	
> 	<[3]/srv/clone{
> 		d=`{<[0=3]read}
> 		bind /srv/$d /srv
> 		# ugly, but we don't want to leak the clone fd into
> 		# procs that may stick around, so write over fd3 again
> 		<[3=0]{
> 			rfork n
> 			bind /usr/web /mnt/static
> 			execfs -m /usr/web /sys/lib/tcp80/gitrules
> 			bind /mnt/static /usr/web/static
> 			rfork n
> 			cd /
> 			exec /bin/tcp80
> 		}
> 	}
> 

Thank you Ori, that was very helpful.  I was surprised to see that the
file is left open when there's an rc error:
	cpu% lc /srv
	acme.glenn.3372	cons			hjfs.cmd		rio.glenn.504
	acme.glenn.908	cs				mntexport		rio.glenn.836
	boot			dns				pin-glenn		slashmnt
	clone			factotum		plumb.glenn.495	slashn
	cpu% </srv/clone { d=`{<f} }
	/fd/0:2: < can't open: f: 'f' not found
	cpu% lc /srv
	36/				cons			mntexport		slashmnt
	acme.glenn.3372	cs				pin-glenn		slashn
	acme.glenn.908	dns				plumb.glenn.495
	boot			factotum		rio.glenn.504
	clone			hjfs.cmd		rio.glenn.836
	cpu% bind -c '#s36' /srv
	cpu% lc /srv
	36/				cons			mntexport		slashmnt
	acme.glenn.3372	cs				pin-glenn		slashn
	acme.glenn.908	dns				plumb.glenn.495
	boot			factotum		rio.glenn.504
	clone			hjfs.cmd		rio.glenn.836
	cpu% bind -c '#s'/36 /srv
	cpu% lc /srv
	clone

When the window is closed, then 36/ finally is cleaned up.