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Ever since we introduced fake reboot, we call qemuProcessKill as a reaction to SHUTDOWN event. Unfortunately, qemu doesn't guarantee it flushed all internal buffers before sending SHUTDOWN, in which case killing the process forcibly may result in (virtual) disk corruption. By sending just SIGTERM without SIGKILL we give qemu time to to flush all buffers and exit. Once qemu exits, we will see an EOF on monitor connection and tear down the domain. In case qemu ignores SIGTERM or just hangs there, the process stays running but that's not any different from a possible hang anytime during the shutdown process so I think it's just fine. Also qemu (since 0.14 until it's fixed) has a bug in SIGTERM processing which causes it not to exit but instead send new SHUTDOWN event and keep waiting. I think the best we can do is to ignore duplicate SHUTDOWN events to avoid a SHUTDOWN-SIGTERM loop and leave the domain in paused state.
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>