Subject: Re: [RFC][PATCH] Notify init when processes are reparented to it
From: Scott James Remnant <scott@canonical.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>, lkml <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>
In-Reply-To: <20081229132305.GA31210@redhat.com>
References: <1230378128.7026.50.camel@quest>
	 <20081227114452.GA2919@zelda.netsplit.com>
	 <20081228092024.GA21673@redhat.com>
	 <20081228220122.62940FC278@magilla.sf.frob.com>
	 <1230551457.4664.0.camel@wing-commander>
	 <20081229132305.GA31210@redhat.com>
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Date: Mon, 29 Dec 2008 07:21:11 -0800
Message-Id: <1230564071.4664.8.camel@wing-commander>
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On Mon, 2008-12-29 at 14:23 +0100, Oleg Nesterov wrote:

> On 12/29, Scott James Remnant wrote:
> >
> > On Sun, 2008-12-28 at 14:01 -0800, Roland McGrath wrote:
> >
> > > I'm highly skeptical that this is a desireable feature at all, and
> > > certainly I find the abuse of siginfo_t.si_status here extremely
> > > questionable.  I think we need a clear explanation of what problems
> > > the feature is intended to address.
> > >
> > Did the original e-mail not address this?
>=20
> Do you mean
>=20
> 	[RFC] Notify init when processes are reparented to it
> 	http://marc.info/?l=3Dlinux-kernel&m=3D123038049428388
>=20
> ?
>=20
> I am not sure I really understand the problem. And thus I can't
> understand how this patch can help.
>=20
No problem ;)  like anything, it's only ever perfectly clear to the guy
who wrote it - and everyone else wonders what he's going on about :p

> > We want to be able to supervise daemons.
>=20
> What do you mean?
>=20
> > Later on, 1002 will die and init will receive SIGCHLD for it.
> >
> > Unfortunately neither the 1001 or 1002 processes are known to init, eve=
n
> > though they are original children of the process it spawned (1000), for
> > init to be notified about them - this has been forgotten.
>=20
> Ok, with this patch /sbin/init knows that 1002 is a descendant
> of apache(1000) which was spwaned by init. What can init do
> with this info?
>=20
Fundamentally init would now know that the apache service terminated,
and with what exit code or by what signal.

Right now, all we know is that a process terminated (and why) - we can't
link that back to a service in any kind of foolproof manner.

With the ability to do that, when the apache service dies, we can log
that in a more useful manner (including marking the service as down) -
but most importantly, we can respawn it!

This is something we can't do with processes that daemonise right now.

Scott

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