linux-kernel - Re: [PATCH] vfs: Add setns support for the mount namespace

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Message-ID: <4FAE4C70.5000804@parallels.com>
Date:	Sat, 12 May 2012 15:41:36 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Al Viro <viro@...IV.linux.org.uk>,
	Daniel Lezcano <dlezcano@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Miklos Szeredi <mszeredi@...e.cz>
Subject: Re: [PATCH] vfs: Add setns support for the mount namespace

On 05/12/2012 12:54 AM, Eric W. Biederman wrote:
> 
> setns support for the mount namespace is a little tricky as an arbitrary
> decision must be made about what to set fs->root and fs->pwd to, as
> there is no expectation of a relationship between the two mount
> namespaces.  Therefore I arbitrarily find the root mount point, and
> follow every mount on top of it to find the top of the mount stack.
> Then I set fs->root and fs->pwd to that location.  The topmost root of
> the mount stack seems like a reasonable place to be.
> 
> Bind mount support for the mount namespace inodes has the possibility of
> creating circular dependencies between mount namespaces.  Circular
> dependencies can result in loops that prevent mount namespaces from
> every being freed.  I avoid creating those circular dependencies by
> adding a sequence number to the mount namespace and require all bind
> mounts be of a younger mount namespace into an older mount namespace.
> 
> Add a helper function proc_ns_inode so it is possible to detect when we
> are attempting to bind mound a namespace inode.
> 
> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>

Acked-by: Pavel Emelyanov <xemul@...allels.com>
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