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

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Date:	Fri, 18 May 2012 16:47:02 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	Pavel Emelyanov <xemul@...allels.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	Daniel Lezcano <dlezcano@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-fsdevel\@vger.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Miklos Szeredi <mszeredi@...e.cz>
Subject: Re: [PATCH] vfs: Add setns support for the mount namespace

"Serge E. Hallyn" <serge@...lyn.com> writes:

> Quoting Pavel Emelyanov (xemul@...allels.com):
>> 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>
>
> These patches haven't made it into linux-next or Linus' tree.  (More
> worrisome, is that the several online linux-kernel mail archives I've
> checked seem to have most of this thread, but not Eric's original
> patch.)  What path were they expected to go in by?

I was hoping Al Viro would pick it up in the vfs tree, or at least
review the patch.  With a backup possibility that Andrew Morton might.

Given that the merge window is likely to open in next couple of days
I plan to resubmit this after the merge window closes. 

I don't have a clue what happened to the archives that day but it does
look like there was a significant mail hiccup as the number of messages
archived are way down.

Eric
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