[libvirt] mdevctl: A shoestring mediated device management and persistence utility

Hi, Currently mediated device management, much like SR-IOV VF management, is largely left as an exercise for the user. This is an attempt to provide something and see where it goes. I doubt we'll solve everyone's needs on the first pass, but maybe we'll solve enough and provide helpers for the rest. Without further ado, I'll point to what I have so far: https://github.com/awilliam/mdevctl This is inspired by driverctl, which is also a bash utility. mdevctl uses udev and systemd to record and recreate mdev devices for persistence and provides a command line utility for querying, listing, starting, stopping, adding, and removing mdev devices. Currently, for better or worse, it considers anything created to be persistent. I can imagine a global configuration option that might disable this and perhaps an autostart flag per mdev device, such that mdevctl might simply "know" about some mdevs but not attempt to create them automatically. Clearly command line usage help, man pages, and packaging are lacking as well, release early, release often, plus this is a discussion starter to see if perhaps this is sufficient to meet some needs. Originally I thought about making a utility to manage both mdev and SR-IOV VFs all in one, but it seemed more natural to start here (besides, I couldn't think of a good name for the combined utility). If this seems useful, maybe I'll start on a vfctl for SR-IOV and we'll see whether they have enough synergy to become one. It would be really useful if s390 folks could help me understand whether it's possible to glean all the information necessary to recreate a ccw or ap mdev device from sysfs. I expect the file where we currently only store the mdev_type to evolve into something that includes more information to facilitate more complicated devices. For now I make no claims to maintaining compatibility of recorded mdev devices, it will absolutely change, but I didn't want to get bogged down in making sure I don't accidentally source a root kit hidden in an mdev config file. I'm also curious how or if libvirt or openstack might use this. If nothing else, it makes libvirt hook scripts easier to write, especially if we add an option not to autostart mdevs, or if users don't mind persistent mdevs, maybe there's nothing more to do. BTW, feel free to clean up by bash, I'm a brute force and ignorance shell coder ;) Thanks, Alex