Re: [Qemu-devel] [PATCH v2 2/2] vl: fix use of --daemonize with --preconfig

[Igor Mammedov <imammedo@redhat.com>]

On Mon,  4 Jun 2018 13:03:45 +0100
Daniel P. Berrangé <berrange@redhat.com> 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 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.
> 
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
[...]

How about combining ideas from yours and Michal's patches?
It should fix broken iotests/libvirt sync point and
we can think about NONE runstate idea at without rushing it.
If it looks acceptable, I'll post proper patches + test case for it
after some testing (to ensure that iotests Max pointed out are working
as expected)

diff --git a/vl.c b/vl.c
index c4fe255..a2062d6 100644
--- a/vl.c
+++ b/vl.c
@@ -1953,10 +1953,15 @@ static bool main_loop_should_exit(void)
 
 static void main_loop(void)
 {
+    static bool os_setup_post_done = false;
 #ifdef CONFIG_PROFILER
     int64_t ti;
 #endif
-    do {
+    if (!os_setup_post_done) {
+        os_setup_post();
+        os_setup_post_done = true;
+    }
+    while (!main_loop_should_exit()) {
 #ifdef CONFIG_PROFILER
         ti = profile_getclock();
 #endif
@@ -1964,7 +1969,7 @@ static void main_loop(void)
 #ifdef CONFIG_PROFILER
         dev_time += profile_getclock() - ti;
 #endif
-    } while (!main_loop_should_exit());
+    }
 }
 
 static void version(void)