linux-kernel - Re: [PATCH] autofs4: turn ->oz

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Message-ID: <20090123080617.GA4002@redhat.com>
Date:	Fri, 23 Jan 2009 09:06:17 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ian Kent <raven@...maw.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, hpa@...or.com,
	Cedric Le Goater <clg@...ibm.com>,
	Dave Hansen <haveblue@...ibm.com>,
	Eric Biederman <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Serge Hallyn <serue@...ibm.com>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] autofs4: turn ->oz_pgrp into "struct pid *"

On 01/23, Ian Kent wrote:
>
> On Sun, 2009-01-18 at 08:34 +0100, Oleg Nesterov wrote:
> >
> > I guess autofs4_show_options()->pid_vnr() is not exactly right, but hopefully
> > not worse than the current code.
>
> But shouldn't pid_vnr(sbi->oz_pgrp) report the pid as seen in the
> namespace of the calling process? In which case the only problem would
> be listing the mount table from a subordinate namespace that cannot see
> the process which did the mount, assuming fs namespace is not linked in
> some strict way to pid namespace, this could give an odd result. What
> might happen in this case Oleg?

Yes, nothing bad can happen. pid_vnr() just returns 0 if the calling
process can't see the namespace.

But I was worried about the case when, say, we are looking at
/subnamespace_root_mount/proc/mounts.

In that case pid_vnr() will report the pid_t in the global namespace,
this differs from the case when this file is read by its own namespace
as /proc/mounts.

I do not know whether this is right or not, though.

Oleg.

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