linux-kernel - Re: Mount namespace "dominant peer group"?

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Message-ID: <f6d3f4b6-a029-d2a4-d3f3-f1e75b48590e@gmail.com>
Date:	Tue, 24 May 2016 17:57:44 -0500
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Miklos Szeredi <mszeredi@...hat.com>
Cc:	mtk.manpages@...il.com, Ram Pai <linuxram@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: Mount namespace "dominant peer group"?

On 05/23/2016 02:55 AM, Miklos Szeredi wrote:
> C is slave of B is slave of A.  If a process can see (i.e. has under
> its root) A and C but not B then for C it will show
> master:B,propagate_from:A.  This piece of information is shown because
> it can't see the immediate master (B) and so cannot determine the
> chain of propagation between the mounts it can see.

Thanks, Miklos!

> Concrete example:

Yep, that does it. Thanks for the walk through!

One piece missing below though, in case anyone else tries to walk
through.

> # mount --bind / /mnt
> # mount --bind /proc /mnt/proc
> # mount --make-private /mnt
> # mount --make-shared /mnt
> # mkdir /tmp/etc
> # mount --bind /mnt/etc /tmp/etc
> # mount --make-slave /tmp/etc
> # mount --make-shared /tmp/etc

# mkdir /mnt/tmp/etc

> # mount --bind /tmp/etc /mnt/tmp/etc
> # mount --make-slave /mnt/tmp/etc
> # cat /proc/self/mountinfo | grep /tmp/etc
> 164 40 253:1 /etc /tmp/etc rw,relatime shared:100 master:97 - ...
> # chroot /mnt
> # cat /proc/self/mountinfo
> 129 62 253:1 / / rw,relatime shared:97 - ...
> 168 129 253:1 /etc /tmp/etc rw,relatime master:100 propagate_from:97 - ...

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/