linux-kernel - Re: [RFC][PATCH 1/4] checkpoint-restart: general infrastructure

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Message-Id: <200808090837.07417.arnd@arndb.de>
Date:	Sat, 9 Aug 2008 08:37:07 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	containers@...ts.linux-foundation.org,
	Theodore Tso <tytso@....edu>, linux-kernel@...r.kernel.org,
	Oren Laadan <orenl@...columbia.edu>
Subject: Re: [RFC][PATCH 1/4] checkpoint-restart: general infrastructure

On Saturday 09 August 2008, Dave Hansen wrote:
> On Sat, 2008-08-09 at 00:39 +0200, Arnd Bergmann wrote:
> > The main problem I see with that would be atomicity: If you want multiple
> > processes to keep interacting with each other, you need to save them at
> > the same point in time, which gets harder as you split your interface into
> > more than a single file descriptor.
> 
> It could take ages to write out a checkpoint even to a single fd, so I
> suspect we'd have the exact same kinds of issues either way.

I guess either way, you have to SIGSTOP (or similar) all the tasks you want
to checkpoint atomically before you start saving the contents.
If you use a single fd, you can do that under the covers, when using a 
more complex file system, it seems more logical to require an explicit
interface for this.

	Arnd <><
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