To: Andrew Morton <akpm@osdl.org>
Cc: Herbert Poetzl <herbert@13thfloor.at>, serue@us.ibm.com,
       linux-kernel@vger.kernel.org, dev@sw.ru, devel@openvz.org,
       sam@vilain.net, xemul@sw.ru, haveblue@us.ibm.com, clg@fr.ibm.com
Subject: Re: [PATCH 0/9] namespaces: Introduction
References: <20060518154700.GA28344@sergelap.austin.ibm.com>
	<20060518103430.080e3523.akpm@osdl.org>
	<20060519124235.GA32304@MAIL.13thfloor.at>
	<20060519081334.06ce452d.akpm@osdl.org>
From: ebiederm@xmission.com (Eric W. Biederman)
Date: Fri, 19 May 2006 10:27:32 -0600
In-Reply-To: <20060519081334.06ce452d.akpm@osdl.org> (Andrew Morton's
 message of "Fri, 19 May 2006 08:13:34 -0700")
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Andrew Morton <akpm@osdl.org> writes:

> Herbert Poetzl <herbert@13thfloor.at> wrote:
>>
>> let me
>>  give a simple example here:
>
> Examples are useful.
>
>>   "pid virtualization"
>> 
>>   - Linux-VServer doesn't really need that right now.
>>     we are perfectly fine with "pid isolation" here, we
>>     only "virtualize" the init pid to make pstree happy
>> 
>>   - Snapshot/Restart and Migration will require "full"
>>     pid virtualization (that's where Eric and OpenVZ
>>     are heading towards)
>
> snapshot/restart/migration worry me.  If they require complete
> serialisation of complex kernel data structures then we have a problem,
> because it means that any time anyone changes such a structure they need to
> update (and test) the serialisation.

There is a strict limit to what is user visible, and if it isn't user visible
we will never need it in a checkpoint.  So internal implementation details
should not matter.

> This may be a show-stopper, in which case maybe we only need to virtualise
> pid #1.

Except we do need something for pid isolation, and a pid namespace is
quite possibly the light weight solution.  If you can't see the pid it is
clearly isolated from you.

> Anyway.  Thanks, guys.  It sound like most of this work will be nicely
> separable so we can think about each bit as it comes along.

Yes, and there are enough issues it is significant.

Eric
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