linux-kernel - Re: [RFC][PATCH 00/11] track files for checkpointability

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Message-ID: <49B15F35.2010909@free.fr>
Date:	Fri, 06 Mar 2009 18:36:53 +0100
From:	Cedric Le Goater <legoater@...e.fr>
To:	"Serge E. Hallyn" <serue@...ibm.com>
CC:	Greg Kurz <gkurz@...ibm.com>,
	containers <containers@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [RFC][PATCH 00/11] track files for checkpointability

Serge E. Hallyn wrote:
> Quoting Greg Kurz (gkurz@...ibm.com):
>> On Fri, 2009-03-06 at 01:00 +0300, Alexey Dobriyan wrote:
>>> On Thu, Mar 05, 2009 at 01:27:07PM -0800, Dave Hansen wrote:
>>>>> Imagine, unsupported file is opened between userspace checks
>>>>> for /proc/*/checkpointable and /proc/*/fdinfo/*/checkpointable
>>>>> and whatever, you stil have to do all the checks inside checkpoint(2).
>>>> Alexey, we have two problems here.  I completely agree that we have to
>>>> do complete and thorough checks of each file descriptor at
>>>> sys_checkpoint().  Any checks made at other times should not be trusted.
>>>>
>>>> The other side is what Ingo has been asking for.  How do we *know* when
>>>> we are checkpointable *before* we call (and without calling)
>>> This "without calling checkpoint(2)" results in much complications
>>> as demonstrated.
>>>
>>> task_struct and file are not like other structures because they are exposed
>>> in /proc. For PROC_FS=n kernels, one can't even check.
>>>
>>> You can do checkpoint(2) without actual dump. You pass, you're most
>>> certainly checkpointable (with inevitable race condition in mind).
>>>
>> Ahhh thank you very much Alexey ! I wanted to explain this to Dave a few
>> monthes ago but I failed... probably because of my poor English skills.
>>
>> https://lists.linux-foundation.org/pipermail/containers/2008-October/013549.html
>>
>> Why would we add checking all over the place when it MUST be done on the
>> sys_checkpoint() path ? The checkpoint(2) dry-run is definitely the way
>> to go.
> 
> I'm sure Dave understood that this was possible :)
> 
> But what you and Alexey are proposing does not and cannot fullfill
> Ingo's requirement.

And if Ingo's requirement is fulfilled, would any C/R patchset be acceptable ?

C.  
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