linux-kernel - Re: [patch 0/8] unprivileged mount syscall

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Message-Id: <E1HcKQd-0001yO-00@dorka.pomaz.szeredi.hu>
Date:	Fri, 13 Apr 2007 13:58:59 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	linuxram@...ibm.com
CC:	serue@...ibm.com, akpm@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, containers@...ts.osdl.org,
	util-linux-ng@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 0/8] unprivileged mount syscall

> On Wed, 2007-04-11 at 12:44 +0200, Miklos Szeredi wrote:
> > > 1. clone the master namespace.
> > > 
> > > 2. in the new namespace
> > > 
> > > 	move the tree under /share/$me to /
> > >         for each ($user, $what, $how) {
> > >             move /share/$user/$what to /$what
> > > 	    if ($how == slave) {
> > >                  make the mount tree under /$what as slave
> > >             }
> > >         }
> > >         
> > > 3. in the new namespace make the tree under 
> > >        /share as private and unmount /share
> > 
> > Thanks.  I get the basic idea now: the namespace itself need not be
> > shared between the sessions, it is enough if "share" propagation is
> > set up between the different namespaces of a user.
> > 
> > I don't yet see either in your or Viro's description how the trees
> > under /share/$USER are initialized.  I guess they are recursively
> > bound from /, and are made slaves.
> 
> yes. I suppose, when a userid is created one of the steps would be
> 
> mount --rbind / /share/$USER
> mount --make-rslave /share/$USER
> mount --make-rshared /share/$USER

Thinking a bit more about this, I'm quite sure most users wouldn't
even want private namespaces.  It would be enough to

  chroot /share/$USER

and be done with it.

Private namespaces are only good for keeping a bunch of mounts
referenced by a group of processes.  But my guess is, that the natural
behavior for users is to see a persistent set of mounts.

If for example they mount something on a remote machine, then log out
from the ssh session and later log back in, they would want to see
their previous mount still there.

Miklos
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