From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from [140.186.70.92] (port=51147 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1PaPYg-0000eE-R5
	for qemu-devel@nongnu.org; Wed, 05 Jan 2011 04:21:31 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <paolo.bonzini@gmail.com>) id 1PaPYf-0002Ra-JP
	for qemu-devel@nongnu.org; Wed, 05 Jan 2011 04:21:30 -0500
Received: from mail-gw0-f45.google.com ([74.125.83.45]:61658)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <paolo.bonzini@gmail.com>) id 1PaPYf-0002RT-Dd
	for qemu-devel@nongnu.org; Wed, 05 Jan 2011 04:21:29 -0500
Received: by gwj23 with SMTP id 23so7545935gwj.4
	for <qemu-devel@nongnu.org>; Wed, 05 Jan 2011 01:21:28 -0800 (PST)
Sender: Paolo Bonzini <paolo.bonzini@gmail.com>
Message-ID: <4D24382E.8080903@redhat.com>
Date: Wed, 05 Jan 2011 10:21:50 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
MIME-Version: 1.0
References: <4D005006.9080307@cn.fujitsu.com>
	<4D07378B.3050901@cn.fujitsu.com>	<4D0EB06D.6060001@cn.fujitsu.com>	<29897010-A575-4C94-8016-C0FC03652B64@web.de>
	<4D102795.9040107@cn.fujitsu.com>
In-Reply-To: <4D102795.9040107@cn.fujitsu.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Subject: [Qemu-devel] Re: [PATCH v2] disable sigcld handling before calling
	pclose()
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/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: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Wen Congyang <wency@cn.fujitsu.com>
Cc: =?ISO-8859-1?Q?Andreas_F=E4rber?= <andreas.faerber@web.de>, qemu-devel <qemu-devel@nongnu.org>, Luiz Capitulino <lcapitulino@redhat.com>

On 12/21/2010 05:05 AM, Wen Congyang wrote:
> When I use the command 'virsh save' to save the domain state,
> I receive the following error message:
> operation failed: Migration unexpectedly failed.
>
> I debug the qemu by adding some printf(), and find the function
> pclose() returns -1.
>
> I use strace to trace qemu, the log is as the following:
> ======
> close(17)                               = 0
> --- SIGCHLD (Child exited) @ 0 (0) ---
> wait4(-1, NULL, WNOHANG, NULL)          = 22016
> rt_sigreturn(0)                         = 0
> wait4(22016, 0x7fff7f1034fc, 0, NULL)   = -1 ECHILD (No child processes)
> ======
>
> We wait the child twice: one is in signal SIGCHLD handling and the other
> one is in pclose().
>
> We should disable sigcld handling before calling pclose().

I wondered whether we need SIGCHLD handling at all.  fork is called only 
from:

- xen_domain_watcher in hw/xen_domainbuild.c

- launch_script in net/tap.c

- SLIRP's fork_exec ("mini inetd")

For the first, the child will always "outlive" the parent.  For the 
second, we do waitpid in the function.  So SLIRP is the only real user 
of the SIGCHLD handler and in fact this:

http://www.google.com/codesearch/p?hl=en#tGk9u3ZS0cw/pub/Linux/system/network/serial/slirp-1.0.9.tar.gz|s3yKHVXI6eg/slirp-1.0.9/src/main.c

suggests that the handler came from there (search for do_wait).  Would 
anybody object to removing the support for Samba under SLIRP and all the 
resulting cruft?

Paolo