[libvirt] [PATCH 00/14] Add a virtlockd lock manager daemon

The lock manager infrastructure we recently added to QEMU only has two possible drivers at this time, 'nop' and 'sanlock'. The former does absolutely nothing, while the latter requires a 3rd party package installed and is a little heavy on disk I/O and storage requirements. This series adds a new daemon 'virtlockd' which is intended to be enabled by default on all hosts running 'libvirtd'. This daemon provides a service for disk locking based on the traditional fcntl() lock primitives. There is a new libvirt manager plugin which talks to this daemon over RPC. The reason for doing the locks in a separate process is that we want the locks to remain active, even if libvirtd crashes, or is restarted. The virtlockd daemon has this one single job so should be pretty reliable and selfcontained. This patch series really benefits from the new RPC APIs, requiring minimal code for the new daemon / client At this time, virtlockd does not lock the actual disk files, but instead creates a lockspace & leases under /var/lib/libvirt/lockd. The lockspace we use for disks is named org.libvirt.lockd.files, and lease names are based on a SHA256 checksum of the fully qualified disk name. eg /var/lib/libvirt/lockd/org.libvirt.lockd.files/adf94fc33a24da1abff7dd7374a9919bb51efee646da8c3ac464c10cd59750bd These leases are all zero-bytes long and no I/O is ever performed on them, only fcntl() is used. So there is material overhead. Whenever creating or deleting leases, we first acquire a lock on /var/lib/libvirt/lockd/org.libvirt.lockd.files/org.libvirt.lockd.index A non-root virtlockd will instead use $HOME/.libvirt/lockd By default we gain protection out of the box against - Starting two guests on the same host with the same disk image not marked with <shareable/> - libvirtd getting confused and forgetting a guest, allowing it to be started for a 2nd time If the admin mounts a shared filesytem (eg NFS) on /var/lib/libvirt/lockd then this protection is extended across all hosts sharing that mount volume. As part of this series, I also introduce support for systemd services for libvirtd and libvir-guests.