[libvirt] RFC [0/3]: A proposal for lock manager plugins

A few weeks back David introduce sync-manager as a means for protecting against the same VM being started on multiple hosts: https://www.redhat.com/archives/libvir-list/2010-August/msg00179.html This is obviously a desirable feature for libvirt, but we don't want to have a hardcoded dependancy on a particular implementation. We can achieve isolation between libvirt & sync-manager, allowing for alternative implementations by specifying a formal plugin for supervisor processes. What follows is my mockup of what a plugin API would look like, its internal libvirt API and an outline of the usage scenarios in psuedo code. At the minimum level of compliance, the plugin implementation provides for per-VM level exclusion. Optionally a plugin can declare that it - supports locks against individual resources (disks) - supports hotplug of individual resources - supports migration of the supervised process Migration/hotplug will be forbid if those capabilities aren't declared by the plugin. In parallel with David's work on sync-manager, I intend to write a simple plugin implementation based solely on fcntl() locking. It is important that we have 2 independant implementations to prove the validity of the plugin API. The fcntl() impl should provide a zero-config impl we can deploy out of the box that will provide protection against 2 vms using the same disk image on a host, and limited protection in multi-host scenarios with shared filesystems (no protection for shared block devs). Perhaps we should have a 3rd impl based on libdlm too, for Red Hat ClusterSuite scenarios, though sync-manager may well be general & simple enough to easily cope with this already. Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://deltacloud.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|