Re: [libvirt PATCH v3 00/21] Add support for persistent mediated devices

This patch series follows the previously-merged series which added support for transient mediated devices. This series expands mdev support to include persistent device definitions. Again, it relies on mdevctl as the backend. It follows the common libvirt pattern of APIs by adding the following new APIs for node devices: - virNodeDeviceDefineXML() - defines a persistent device - virNodeDeviceUndefine() - undefines a persistent device - virNodeDeviceCreate() - starts a previously-defined device It also adds virsh commands mapping to these new APIs: nodedev-define, nodedev-undefine, and nodedev-start. Since we rely on mdevctl for the definition of ediated devices, we need a way to stay up-to-date with devices that are defined by mdevctl (outside of libvirt). The method for staying up-to-date is currently a little bit crude due to the fact that mdevctl does not emit any events when new devices are added or removed. As a workaround, we create a file monitor for the mdevctl config directory and re-query mdevctl when we detect changes within that directory. In the future, mdevctl may introduce a more elegant solution. changes in v3: - streamlined tests -- removed some unnecessary duplication - split out patch to factor out node device name generation function - split nodeDeviceParseMdevctlChildDevice() into a separate function - added follow-up patch to remove space-padded alignment in header - refactored the mdevctl update handling significantly: - no longer a separate persistent thread that gets signaled by a timer - now piggybacks onto the existing udev thread and signals the thread in t= he same way that the udev event does. - Daniel suggested spawning a throw-away thread to handle mdevctl updates, but that introduces the complexity of possibly serializing multiple throw-away threads (e.g. if we get an 'created' event followed immediate= ly by a 'deleted' event, two threads may be spawned and we'd need to ensure they are properly ordered) - added virNodeDeviceObjListForEach() and virNodeDeviceObjListRemoveLocked() to simplify removing devices that are removed from mdevctl. - coding style fixes - NOTE: per Erik's request, I experimented with changing the way that mdevctl commands were generated and tested (e.g. introducing something like virMdevctlGetCommand(def, MDEVCTL_COMMAND_<SUBCOMMAND>, ...)), but it was too invasive and awkward and didn't seem worthwhile