From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
Subject: Re: [RFC 0/4] per-namespace allowed filesystems list
Date: Mon, 23 Jan 2012 23:12:39 +0000
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To: "Kirill A. Shutemov" <kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org>
Cc: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org, serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org, daniel.lezcano-GANU6spQydw@public.gmane.org, pjt-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, mzxreary-uLTowLwuiw4b1SvskN2V4Q@public.gmane.org, xemul-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org, James.Bottomley-d9PhHud1JfjCXq6kfMZ53/egYHeGw8Jk@public.gmane.org, tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, eric.dumazet-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org

On Tue, Jan 24, 2012 at 01:04:57AM +0200, Kirill A. Shutemov wrote:
> On Mon, Jan 23, 2012 at 09:12:19PM +0000, Al Viro wrote:
> > This is bloody ridiculous; if you want to prevent a luser adming playing with
> > the set of mounts you've given it, the right way to go is not to mess with the
> > "which fs types are allowed" but to add a per-namespace "immutable" flag.
> > And add a new clone(2)/unshare(2) flag, used only along with the CLONE_NEWNS
> > and setting the "immutable" on the copied namespace.
> 
> How will it work if we want to allow namespaced environment to mount block
> devices, but not, let say, debugfs?
> 
> Differentiation between filesystem type and source is one of broken things
> in Unix API.

Translation, please?

> I don't see an easy way to fix it. Only plan9. :)

Huh?  Plan 9 does *not* contain anything of that kind.  And their '#<letter>'
convention for in-kernel filesystems is one of the uglier things about their
API, IMO...