On Mon, Jun 11, 2018 at 03:16:25PM +0200, Igor Mammedov wrote: > On Fri, 8 Jun 2018 10:21:05 -0300 > Eduardo Habkost <ehabk...@redhat.com> wrote: > > > 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 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. > > > > > > This is a chicken and egg problem, leading to deadlock at startup. > > > > > > 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 started > > > successfully, so not be expecting an abrupt exit. Moving as much user > > > input validation as possible to before the main_loop() call might help, > > > but mgmt application should stop assuming that QEMU has started > > > successfuly and use other means to collect errors from QEMU (logfile). > > > > > > Signed-off-by: Daniel P. Berrangé <berra...@redhat.com> > > > Signed-off-by: Igor Mammedov <imamm...@redhat.com> > > > --- > > > 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 --preconfig > > > 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 was in v4 > > > > > > CC: berra...@redhat.com > > > CC: mre...@redhat.com > > > CC: pbonz...@redhat.com > > > CC: ehabk...@redhat.com > > > CC: ldok...@redhat.com > > > CC: ebl...@redhat.com > > > --- > > > os-posix.c | 6 ++++++ > > > vl.c | 6 ++++++ > > > 2 files changed, 12 insertions(+) > > > > > > 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) > > > > > > void os_setup_post(void) > > > { > > > + static bool os_setup_post_done; > > > int fd = 0; > > > > > > + if (os_setup_post_done) { > > > + return; > > > + } > > > + os_setup_post_done = true; > > > + > > > if (daemonize) { > > > if (chdir("/")) { > > > error_report("not able to chdir to /: %s", strerror(errno)); > > > 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); > > > > > > /* 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(); > > > + } > > > > 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: > > > > * 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 > > 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. > > > * 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, > > * move init code that opens files to early stage (before preconfig monitor) > or split it to open files early. > (I've spotted several obvious places fwcfg/vnc/replay_start/migration) > 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? > > * 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. -- Eduardo