From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51047) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fSS8s-0000bo-50 for qemu-devel@nongnu.org; Mon, 11 Jun 2018 15:06:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fSS8p-0004lt-0C for qemu-devel@nongnu.org; Mon, 11 Jun 2018 15:06:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54536) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fSS8o-0004lJ-Nj for qemu-devel@nongnu.org; Mon, 11 Jun 2018 15:06:10 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DF1CF804F5 for ; Mon, 11 Jun 2018 19:06:09 +0000 (UTC) Date: Mon, 11 Jun 2018 16:06:07 -0300 From: Eduardo Habkost Message-ID: <20180611190607.GU7451@localhost.localdomain> References: <20180606135051.GR7451@localhost.localdomain> <1528372809-175770-1-git-send-email-imammedo@redhat.com> <20180608132105.GA24764@localhost.localdomain> <20180611151625.4b2420b8@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20180611151625.4b2420b8@redhat.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v6 2/2] vl: fix use of --daemonize with --preconfig List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Igor Mammedov Cc: qemu-devel@nongnu.org, ldoktor@redhat.com, mreitz@redhat.com, pbonzini@redhat.com, Eric Blake , "Daniel P. Berrange" , Markus Armbruster On Mon, Jun 11, 2018 at 03:16:25PM +0200, Igor Mammedov wrote: > On Fri, 8 Jun 2018 10:21:05 -0300 > Eduardo Habkost wrote: >=20 > > On Thu, Jun 07, 2018 at 02:00:09PM +0200, Igor Mammedov 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 pare= nt > > > process won't exit until the mgmt application connects to the monit= or > > > and tells QEMU to leave the RUN_STATE_PRECONFIG. The mgmt applicati= on > > > 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 --preconfig is used. 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 starte= d > > > successfully, so not be expecting an abrupt exit. Moving as much us= er > > > input validation as possible to before the main_loop() call might h= elp, > > > but mgmt application should stop assuming that QEMU has started > > > successfuly and use other means to collect errors from QEMU (logfil= e). > > >=20 > > > Signed-off-by: Daniel P. Berrang=E9 > > > Signed-off-by: Igor Mammedov > > > --- > > > v5: > > > * use original Daniel's patch [1], but addapt it to apply on top = of > > > "[PATCH v3 1/2] cli: Don't run early event loop if no --precon= fig was specified" > > > with extra comment and massage commit message a little bit. > > > v6: > > > * hide os_setup_post_done flag inside of os_setup_post() as it wa= s in v4 > > >=20 > > > CC: berrange@redhat.com > > > CC: mreitz@redhat.com > > > CC: pbonzini@redhat.com > > > CC: ehabkost@redhat.com > > > CC: ldoktor@redhat.com > > > CC: eblake@redhat.com > > > --- > > > os-posix.c | 6 ++++++ > > > vl.c | 6 ++++++ > > > 2 files changed, 12 insertions(+) > > >=20 > > > diff --git a/os-posix.c b/os-posix.c > > > index 9ce6f74..0246195 100644 > > > --- a/os-posix.c > > > +++ b/os-posix.c > > > @@ -309,8 +309,14 @@ void os_daemonize(void) > > > =20 > > > void os_setup_post(void) > > > { > > > + static bool os_setup_post_done; > > > int fd =3D 0; > > > =20 > > > + if (os_setup_post_done) { > > > + return; > > > + } > > > + os_setup_post_done =3D true; > > > + > > > if (daemonize) { > > > if (chdir("/")) { > > > error_report("not able to chdir to /: %s", strerror(er= rno)); > > > diff --git a/vl.c b/vl.c > > > index fa44138..457ff2a 100644 > > > --- a/vl.c > > > +++ b/vl.c > > > @@ -4578,6 +4578,12 @@ int main(int argc, char **argv, char **envp) > > > parse_numa_opts(current_machine); > > > =20 > > > /* do monitor/qmp handling at preconfig state if requested */ > > > + if (!preconfig_exit_requested && is_daemonized()) { > > > + /* signal parent QEMU to exit, libvirt treats it as a sign > > > + * that monitor socket is ready to accept connections > > > + */ > > > + os_setup_post(); > > > + } =20 > >=20 > > I was looking at the daemonize logic, and noticed it we have a > > huge amount of code between this line and the next > > os_setup_post() call that could either: > >=20 > > * call exit() and/or error_report(); or > logging would work to the extent mentioned in commit message, > i.e. it' would work fine when log file is used otherwise it > errors will go to /dev/null >=20 > so it should be more or less fine on this point My worry is that most users of error_report() involve an exit() call too. Once we have an active monitor, we must never call exit() directly. Even qmp_quit() doesn't call exit() directly. >=20 > > * be unable to finish machine initialization because of > > chdir("/"), change_root(), or change_process_uid(). > this one really no go. > I see 2 options here, >=20 > * move init code that opens files to early stage (before preconfig mon= itor) > or split it to open files early. > (I've spotted several obvious places fwcfg/vnc/replay_start/migratio= n) > but there might be code somewhere in callbacks that would do it too, > so it rather risky to go this route. > (I'd do this anyways one place at the time using sanitizing > initialization sequence pretext.) We might have QMP commands that take file paths as input, so is this really an option? >=20 > * split out signaling part that tells parent process to exit into > separate helper that's called once before/from main_loop(). > This option seems low risk and additionally error output to > stderr will work as it does currently (until os_setup_post()) My assumption is that separating the chdir()/stdout/stderr logic from the fork/daemonize/exit steps wouldn't be possible without breaking expectations about -daemonize. --=20 Eduardo