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We were not directly saving the domain XML to file after starting or finishing a blockcopy. Without the startup write, a libvirtd restart in the middle of a copy job would forget that the job was underway. Then at pivot, we were indirectly writing new XML in reaction to events that occur as we stop and restart the guest CPUs. But there was a race: since pivot is an async action, it is possible that libvirtd is restarted before the pivot completes, so if XML changes during the event, that change was not written. The original blockcopy code cleared out the <mirror> element prior to restarting the CPUs, but this is also a race, observed if a user does an async pivot and a dumpxml before the event occurs. Furthermore, this race will interfere with active commit in a future patch, because that code will rely on the <mirror> element at the time of the qemu event to determine whether to inform the user of a normal commit or an active commit. Fix things by saving state any time we modify live XML, while delaying XML disk modifications until after the event completes. We still need a to teach libvirtd restarts to examine all existing <mirror> elements to see if the job completed in the meantime (that is, if libvirtd misses the event, the updated state still needs to be updated in live XML), but that will be a later patch, in part because we also need to to start taking advantage of newer qemu's ability to keep the job around after completion rather than the current usage where the job disappears both on error and on success. * src/qemu/qemu_driver.c (qemuDomainBlockCopy): Track XML change on disk. (qemuDomainBlockJobImpl, qemuDomainBlockPivot): Move job-end XML rewrites... * src/qemu/qemu_process.c (qemuProcessHandleBlockJob): ...here. Signed-off-by: Eric Blake <eblake@redhat.com>
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>