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

[Martin Kletzander <mkletzan@redhat.com>]

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On Wed, Feb 08, 2023 at 06:13:10PM -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@redhat.com>

Reviewed-by: Martin Kletzander <mkletzan@redhat.com>

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