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

[Michal Privoznik <mprivozn@redhat.com>]

On 06/04/2018 02:03 PM, Daniel P. Berrangé 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>
> ---
>  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 <mprivozn@redhat.com>

(if my R-b line means anything here :-))

Michal