Date: Thu, 13 Jan 2005 09:55:20 -0800
From: Greg KH <greg@kroah.com>
To: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Al Viro <viro@parcelfarce.linux.theplanet.co.uk>,
       Arjan van de Ven <arjan@infradead.org>, akpm@osdl.org,
       linux-kernel@vger.kernel.org, jtk@us.ibm.com, wtaber@us.ibm.com,
       pbadari@us.ibm.com, markv@us.ibm.com, tytso@us.ibm.com,
       suparna@in.ibm.com
Subject: Re: [PATCH] fs: Restore files_lock and set_fs_root exports
Message-ID: <20050113175520.GA24349@kroah.com>
References: <20050106190538.GB1618@us.ibm.com> <1105039259.4468.9.camel@laptopd505.fenrus.org> <20050106201531.GJ1292@us.ibm.com> <20050106203258.GN26051@parcelfarce.linux.theplanet.co.uk> <20050106210408.GM1292@us.ibm.com> <20050106212417.GQ26051@parcelfarce.linux.theplanet.co.uk> <20050107010119.GS1292@us.ibm.com> <20050113025157.GA2849@us.ibm.com> <20050113170712.GA867@us.ibm.com> <20050113174428.GD1269@us.ibm.com>
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On Thu, Jan 13, 2005 at 09:44:28AM -0800, Paul E. McKenney wrote:
> On Thu, Jan 13, 2005 at 09:07:12AM -0800, Greg KH wrote:
> > On Wed, Jan 12, 2005 at 06:51:57PM -0800, Paul E. McKenney wrote:
> > > 
> > > The current hope is that adding (a) shared and asymmetrically shared
> > > subtrees between namespaces/locations in the same namespace, (b) stackable
> > > LSM modules, and (c) dynamic recursive union mount would enable Linux
> > > to provide this in a technically sound manner.  [But this is not clear
> > > to me yet.]
> > 
> > I don't see how (b) has anything to do with this.  Anyone care to
> > explain that?
> 
> It would allow tracking the processes that are using a given view,
> so that state associated with that view could be cleaned up when the
> last process exits.  One case that motivates this approach:
> 
> 1.	one process creates a view (e.g,. "setview" so that
> 	"/vob/foo/bar.c" references version 1.2, just as
> 	"/views/v1.2/vob/foo/bar.c" would),
> 
> 2.	this process forks off several descendants, then exits, and
> 
> 3.	the descendant processes eventually exit.
> 
> The underlying filesystem could use stackable LSM modules to track fork()s
> and exit()s, allowing it to work out when all processes using a given
> view had terminated.

But why the "stackable" requirement?  Why not just use the LSM interface
and be done with it?

Or do you want to combine this LSM with SELinux or any other LSM
(root-plug, seclvl, etc.)?  If so, that's asking for trouble (see the
stackable LSM problems that have been posted multiple times here, and on
the linux-security-modules mailing list.)

thanks,

greg k-h
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