Hi, Reading http://libvirt.org/hooks.html I'm wondering of the following implication is accurate: Under "QEMU guest migration" it says At the beginning of the migration, the qemu hook script on the _destination_ host is executed with the "start" operation. Above that, under "Specifics" Before a QEMU guest is started, the qemu hook script is called in two locations; if either location fails, the guest is not started. The first location, since 0.9.0, is before libvirt performs any resource labeling.... This is called as: /etc/libvirt/hooks/qemu guest_name prepare begin - The second location, available Since 0.8.0, occurs after libvirt has finished labeling all resources, but has not yet started the guest, called as: /etc/libvirt/hooks/qemu guest_name start begin - Is it accurate that under 0.9.x, starting a VM will run the qemu hook script as both "prepare" and "start," but migrating a VM will only run the qemu hook script as "start"? Or is the description incomplete with libvirt also running "prepare" on migration? Another question, under "Calling libvirt functions from within a hook script" it says DO NOT DO THIS! A hook script must not call back into libvirt, as the libvirt daemon is already waiting for the script to exit. A deadlock is likely to occur. That makes obvious sense. But does it apply to calling libvirt on a second system? For example, a script might check the status of VMs on a second system as a condition of starting a VM on first, using virsh. My guess is that shouldn't deadlock. But then since during migration "the qemu hook script on the _destination_ host is executed," if the destination hook script were in turn to use virsh to check the _source_ host, then in a roundabout way a libvirt function has been called from within the hook script. I can't quite picture whether this particular instance would be dangerous. If it's accurate that the _destination_ hook script is only called with "start" and not with "prepare," the second question matters less. The checks on the second system that I want to do can be limited to the "prepare" invocation, and so never loop back. On the other hand, if the destination hook script _is_ called with "prepare" during migration, it would be useful to know how to tell if it's being called as part of a migration. TIA, Whit
