linux-kernel - Re: [PATCH 1/2] autofs4: allow autofs to work outside the initial PID namespace

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Message-ID: <CAJfpegsqwd57NdHVhwfdNjauj8HKJb=x+2GAZtJQ8vLdt+A=sw@mail.gmail.com>
Date:	Mon, 26 Nov 2012 09:05:46 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Ian Kent <raven@...maw.net>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	autofs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, sukadev@...ux.vnet.ibm.com,
	serge.hallyn@...onical.com, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 1/2] autofs4: allow autofs to work outside the initial PID namespace

On Mon, Nov 26, 2012 at 3:29 AM, Ian Kent <raven@...maw.net> wrote:
>> > > MS_UNBINDABLE says:  skip this mount when copying a mount tree, such
>> > > as when the mount namespace is cloned.
>> > >
>> > > If you set MS_UNBINDABLE on autofs mounts then they will simply not
>> > > appear in a cloned namespace.  Which sounds like a good idea,  no?
>> >
>> > Good point.  If the desire is for a mount to be managed by autofs
>> > setting MS_UNBINDABLE seems required.
>>
>> Arrgh, I know that's something I should have looked into long ago.
>> The fact is that autofs mounts are directly related to a specific path
>> defined by automount maps that are associated with the daemon so bind
>> mounting them elsewhere makes no sense.
>
> Except, AFAICS, they do appear in the clone.

Hmm, yes, apparently the semantics of MS_UNBINDABLE only apply to
actual bind mounts not to namespace cloning. Even though the two
operations are closely related.  Not sure why this is so, but it is
probably not a good idea to change the semantics at this point.

Thanks,
Miklos
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