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When libvirt's virDomainDestroy API is shutting down the qemu process, it first sends SIGTERM, then waits for 1.6 seconds and, if it sees the process still there, sends a SIGKILL. There have been reports that this behavior can lead to data loss because the guest running in qemu doesn't have time to flush its disk cache buffers before it's unceremoniously whacked. This patch maintains that default behavior, but provides a new flag VIR_DOMAIN_DESTROY_GRACEFUL to alter the behavior. If this flag is set in the call to virDomainDestroyFlags, SIGKILL will never be sent to the qemu process; instead, if the timeout is reached and the qemu process still exists, virDomainDestroy will return an error. Once this patch is in, the recommended method for applications to call virDomainDestroyFlags will be with VIR_DOMAIN_DESTROY_GRACEFUL included. If that fails, then the application can decide if and when to call virDomainDestroyFlags again without VIR_DOMAIN_DESTROY_GRACEFUL (to force the issue with SIGKILL). (Note that this does not address the issue of existing applications that have not yet been modified to use VIR_DOMAIN_DESTROY_GRACEFUL. That is a separate patch.)
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>