From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:41578)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1VUCLm-0001jw-9u
	for qemu-devel@nongnu.org; Thu, 10 Oct 2013 05:16:14 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1VUCLd-0005UZ-TC
	for qemu-devel@nongnu.org; Thu, 10 Oct 2013 05:16:06 -0400
Received: from mail-bk0-x231.google.com ([2a00:1450:4008:c01::231]:60386)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1VUCLd-0005Ry-Gm
	for qemu-devel@nongnu.org; Thu, 10 Oct 2013 05:15:57 -0400
Received: by mail-bk0-f49.google.com with SMTP id r7so825481bkg.8
	for <qemu-devel@nongnu.org>; Thu, 10 Oct 2013 02:15:56 -0700 (PDT)
Date: Thu, 10 Oct 2013 11:15:54 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20131010091554.GA11408@stefanha-thinkpad.redhat.com>
References: <CAJSP0QWCzMyJ_Q8ebZHtZUDkgcJhzc2JvMHAfgurxbH5x+dh-A@mail.gmail.com>
	<CE7417FD.911A%markt@netqa.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CE7417FD.911A%markt@netqa.com>
Subject: Re: [Qemu-devel] [Nbd]  Hibernate and qemu-nbd
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: Mark Trumpold <markt@netqa.com>
Cc: nbd-general@lists.sourceforge.net, Wouter Verhelst <w@uter.be>, bonzini@stefanha-thinkpad.redhat.com, Paul Clements <Paul.Clements@steeleye.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

On Fri, Oct 04, 2013 at 07:30:45AM -0700, Mark Trumpold wrote:
> 
> 
> On 9/26/13 10:18 PM, "Stefan Hajnoczi" <stefanha@gmail.com> wrote:
> 
> >
> >Try the qemu-nbd --persistent option.  That should prevent it from
> >shutting down when nbd-client is disconnected.
> >
> >Stefan
> >
> 
> 
> Hi Stefan,
> 
> Sorry for the delay..
> I tried the following per your suggestion:
> 
>   920  qemu-nbd --persistent -p 2000 /root/qemu/q1.img &
>   921  nbd-client -persist localhost 2000 /dev/nbd0
>   922  fsck /dev/nbd0
>   923  mount /dev/nbd0 /mnt
>   924  ls /mnt
>   925  umount /dev/nbd0
>   ::
> 
>   927  echo reboot >/sys/power/disk
>   928  echo disk >/sys/power/state
>   929  mount /dev/nbd0 /mnt
> 
> This seems to work; that is both sides (client and server) persist
> after the hibernate cycle.
> 
> However, if I don't 'umount' '/dev/nbd0' before the hibernate
> cycle, and try to 'ls /mnt' after, the 'ls' hangs indefinitely.
> 
> For my real use case we have the root filesystem mounted,
> so unmounting is not an option (at least I don't think so).
> 
> I also tried remounting readonly, and also 'blockdev --flushbufs ..'
> before the hibernate cycle -- either or both did not help.
> 
> I had thought about trying a 'chroot' and then a 'umount', but
> have not yet tried this.
> 
> This one was so close..

Too bad.  I'm sure it's solvable but would require more debugging and
writing qemu-nbd.c and kernel nbd.c fixes.  Unfortunately I don't have
time to look into it myself.

Stefan