From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50597) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fPqMq-0000nA-C0 for qemu-devel@nongnu.org; Mon, 04 Jun 2018 10:21:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fPqMp-0000gk-E4 for qemu-devel@nongnu.org; Mon, 04 Jun 2018 10:21:52 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:56704 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fPqMp-0000gc-9M for qemu-devel@nongnu.org; Mon, 04 Jun 2018 10:21:51 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E89294022414 for ; Mon, 4 Jun 2018 14:21:50 +0000 (UTC) References: <20180604120345.12955-1-berrange@redhat.com> <20180604120345.12955-3-berrange@redhat.com> From: Michal Privoznik Message-ID: Date: Mon, 4 Jun 2018 16:21:48 +0200 MIME-Version: 1.0 In-Reply-To: <20180604120345.12955-3-berrange@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v2 2/2] vl: fix use of --daemonize with --preconfig List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "=?UTF-8?Q?Daniel_P._Berrang=c3=a9?=" , qemu-devel@nongnu.org Cc: Igor Mammedov , Eric Blake , Paolo Bonzini , Markus Armbruster , Max Reitz On 06/04/2018 02:03 PM, Daniel P. Berrang=C3=A9 wrote: > When using --daemonize, the initial lead process will fork a child and > then wait to be notified that setup is complete via a pipe, before it > exits. When using --preconfig there is an extra call to main_loop() > before the notification is done from os_setup_post(). Thus the parent > process won't exit until the mgmt application connects to the monitor > and tells QEMU to leave the RUN_STATE_PRECONFIG. The mgmt application > won't connect to the monitor until daemonizing has completed though. >=20 > This is a chicken and egg problem, leading to deadlock at startup. >=20 > The only viable way to fix this is to call os_setup_post() before > the early main_loop() call when in RUN_STATE_PRECONFIG. This has the > downside that any errors from this point onwards won't be handled > well by the mgmt application, because it will think QEMU has started > successfully, so not be expecting an abrupt exit. The only way to > deal with that is to move as much user input validation as possible > to before the main_loop() call. This is left as an exercise for > future interested developers. >=20 > Signed-off-by: Daniel P. Berrang=C3=A9 > --- > vl.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) Yup, this fixes the problem I've raised in my patch. Thanks! Reviewed-by: Michal Privoznik (if my R-b line means anything here :-)) Michal