[libvirt PATCH] qemu: allow passt to self-daemonize

[Peter Krempa]

On Wed, Feb 08, 2023 at 18:13:10 -0500, Laine Stump wrote:
> I initially had the passt process being started in an identical
> fashion to the slirp-helper - libvirt was daemonizing the new process
> and recording its pid in a pidfile. The problem with this is that,
> since it is daemonized immediately, any startup error in passt happens
> after the daemonization, and thus isn't seen by libvirt - libvirt
> believes that the process has started successfully and continues on
> its merry way. The result was that sometimes a guest would be started,
> but there would be no passt process for qemu to use for network
> traffic.
> 
> Instead, we should be starting passt in the same manner we start
> dnsmasq - we just exec it as normal (along with a request that passt
> create the pidfile, which is just another option on the passt
> commandline) and wait for the child process to exit; passt then has a
> chance to parse its commandline and complete all the setup prior to
> daemonizing itself; if it encounters an error and exits with a non-0
> code, libvirt will see the code and know about the failure. We can
> then grab the output from stderr, log that so the "user" has some idea
> of what went wrong, and then fail the guest startup.
> 
> Signed-off-by: Laine Stump <laine at redhat.com>
> ---
>  src/qemu/qemu_passt.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)

[..]

>      if (cmdret < 0 || exitstatus != 0) {
>          virReportError(VIR_ERR_INTERNAL_ERROR,
> -                       _("Could not start 'passt'. exitstatus: %d"), exitstatus);
> +                       _("Could not start 'passt': %s"), errbuf);
>          goto error;
>      }

So the 'passt' binary doesn't do any logging later on during runtime
which we'd have to capture into a specific log file?

For this patch:

Reviewed-by: Peter Krempa <pkrempa at redhat.com>