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 * be unable to finish machine initialization because of chdir("/"), change_root(), or change_process_uid(). Doesn't this make -preconfig and -daemonize fundamentally incompatible? > main_loop(); > > /* from here on runstate is RUN_STATE_PRELAUNCH */ > -- > 2.7.4 > > -- Eduardo