From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:45835)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1UIgv3-0000jE-37
	for qemu-devel@nongnu.org; Thu, 21 Mar 2013 10:56:46 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1UIgv1-0004vx-IG
	for qemu-devel@nongnu.org; Thu, 21 Mar 2013 10:56:41 -0400
Received: from mail-we0-x22f.google.com ([2a00:1450:400c:c03::22f]:54518)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1UIgv1-0004vg-Af
	for qemu-devel@nongnu.org; Thu, 21 Mar 2013 10:56:39 -0400
Received: by mail-we0-f175.google.com with SMTP id t11so278622wey.20
	for <qemu-devel@nongnu.org>; Thu, 21 Mar 2013 07:56:38 -0700 (PDT)
Date: Thu, 21 Mar 2013 15:56:30 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20130321145630.GA16677@stefanha-thinkpad.redhat.com>
References: <5142CCB6.7000004@linux.vnet.ibm.com> <51471686.3030505@redhat.com>
	<514AABFC.1030605@linux.vnet.ibm.com> <514AF393.8030109@redhat.com>
	<20130321133802.GA15276@stefanha-thinkpad.redhat.com>
	<514B0E3F.5070309@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <514B0E3F.5070309@redhat.com>
Subject: Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Pavel Hrdina <phrdina@redhat.com>, Juan Quintela <quintela@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, Dietmar Maurer <dietmar@proxmox.com>, Wenchao Xia <xiawenc@linux.vnet.ibm.com>

On Thu, Mar 21, 2013 at 02:42:23PM +0100, Paolo Bonzini wrote:
> Il 21/03/2013 14:38, Stefan Hajnoczi ha scritto:
> > There already is a guest RAM cloning mechanism: fork the QEMU process.
> > Then you have a copy-on-write guest RAM.
> > 
> > In a little more detail:
> > 
> > 1. save non-RAM device state
> > 2. quiesce QEMU to a state that is safe for forking
> > 3. create an EventNotifier for live savevm completion signal
> > 4. fork and pass completion EventNotifier to child
> > 5. parent continues running VM
> > 6. child performs vmsave of copy-on-write guest RAM
> > 7. child signals completion EventNotifier and terminates
> > 8. parent raises live savevm completion QMP event
> 
> Forking a threaded program is not so easy, but it could be done if the
> child is very simple and only uses syscalls to communicate back with the
> parent:

On Linux you should be able to use clone(2) to spawn a thread with
copy-on-write memory.  Too bad it's not portable because it gets around
the messy fork issues.

Stefan