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The current sanlock plugin requires a central management application to manually add <lease> elements to each guest, to protect resources that are assigned to it (eg writable disks). This makes the sanlock plugin useless for usage in more ad hoc deployment environments where there is no central authority to associate disks with leases. This patch adds a mode where the sanlock plugin will automatically create leases for each assigned read-write disk, using a md5 checksum of the fully qualified disk path. This can work pretty well if guests are using stable disk paths for block devices eg /dev/disk/by-path/XXXX symlinks, or if all hosts have NFS volumes mounted in a consistent pattern. The plugin will create one lockspace for managing disks with filename /var/lib/libvirt/sanlock/__LIBVIRT__DISKS__. For each VM disks, there will be another file to hold a lease /var/lib/libvirt/sanlock/5903e5d25e087e60a20fe4566fab41fd Each VM disk lease is usually 1 MB in size. The script virt-sanlock-cleanup should be run periodically to remove unused lease files from the lockspace directory. To make use of this capability the admin will need to do several tasks: - Mount an NFS volume (or other shared filesystem) on /var/lib/libvirt/sanlock - Configure 'host_id' in /etc/libvirt/qemu-sanlock.conf with a unique value for each host with the same NFS mount - Toggle the 'auto_disk_leases' parameter in qemu-sanlock.conf Technically the first step can be skipped, in which case sanlock will only protect against 2 vms on the same host using the same disk (or the same VM being started twice due to error by libvirt). * src/locking/libvirt_sanlock.aug, src/locking/sanlock.conf, src/locking/test_libvirt_sanlock.aug: Add config params for configuring auto lease setup * libvirt.spec.in: Add virt-sanlock-cleanup program, man page * tools/virt-sanlock-cleanup.in: Script to purge unused disk resource lease files
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>