[ovirt-devel] logging VDSM-generated libvirt XML properly

Hello developers! I've been chasing a bug that lead me to an idea of improving our XML logging. Now, to see a VMs generated libvirt XML, we have to rely on vdsm.log. The issue is that the log is rotating and therefore, it is easy to miss the correct XML when dealing with busy hypervisor. Since we're built on libvirt, I was thinking of doing similar thinks that libvirt does with qemu commandline. Each running domain(VM) has it's command line logged in /var/log/libvirt/qemu/${vmname}. This is great for debugging as you can mostly just take the cmdline and restart the VM. There is an issue with using the cmdline directly - networking. Libvirt uses additional script to create and up a bridge. Therefore, it is easier to use the XML and shape it to one's needs. I propose that we properly log the generated XML in a similar fashion as libvirt generates the cmdline. This means we would have path like /var/log/vdsm/libvirt/${vmname}, where generated XML would be stored. To minimize the logging requirements, only last definition of VM with that name may be stored. Additionally, exception level errors related to that VM could also be stored there. What do you think, can we afford the space and additional writes per VM to help the debugging process? Regards, mpolednik