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Each <domainsnapshot> can now contain an optional <memory> element that describes how the VM state was handled, similar to disk snapshots. The new element will always appear in output; for back-compat, an input that lacks the element will assume 'no' or 'internal' according to the domain state. Along with this change, it is now possible to pass <disks> in the XML for an offline snapshot; this also needs to be wired up in a future patch, to make it possible to choose internal vs. external on a per-disk basis for each disk in an offline domain. At that point, using the --disk-only flag for an offline domain will be able to work. For some examples below, remember that qemu supports the following snapshot actions: qemu-img: offline external and internal disk savevm: online internal VM and disk migrate: online external VM transaction: online external disk ===== <domainsnapshot> <memory snapshot='no'/> ... </domainsnapshot> implies that there is no VM state saved (mandatory for offline and disk-only snapshots, not possible otherwise); using qemu-img for offline domains and transaction for online. ===== <domainsnapshot> <memory snapshot='internal'/> ... </domainsnapshot> state is saved inside one of the disks (as in qemu's 'savevm' system checkpoint implementation). If needed in the future, we can also add an attribute pointing out _which_ disk saved the internal state; maybe disk='vda'. ===== <domainsnapshot> <memory snapshot='external' file='/path/to/state'/> ... </domainsnapshot> This is not wired up yet, but future patches will allow this to control a combination of 'virsh save /path/to/state' plus disk snapshots from the same point in time. ===== So for 1.0.1 (and later, as needed), I plan to implement this table of combinations, with '*' designating new code and '+' designating existing code reached through new combinations of xml and/or the existing DISK_ONLY flag: domain memory disk disk-only | result ----------------------------------------- offline omit omit any | memory=no disk=int, via qemu-img offline no omit any |+memory=no disk=int, via qemu-img offline omit/no no any | invalid combination (nothing to snapshot) offline omit/no int any |+memory=no disk=int, via qemu-img offline omit/no ext any |*memory=no disk=ext, via qemu-img offline int/ext any any | invalid combination (no memory to save) online omit omit off | memory=int disk=int, via savevm online omit omit on | memory=no disk=default, via transaction online omit no/ext off | unsupported for now online omit no on | invalid combination (nothing to snapshot) online omit ext on | memory=no disk=ext, via transaction online omit int off |+memory=int disk=int, via savevm online omit int on | unsupported for now online no omit any |+memory=no disk=default, via transaction online no no any | invalid combination (nothing to snapshot) online no int any | unsupported for now online no ext any |+memory=no disk=ext, via transaction online int/ext any on | invalid combination (disk-only vs. memory) online int omit off |+memory=int disk=int, via savevm online int no/ext off | unsupported for now online int int off |+memory=int disk=int, via savevm online ext omit off |*memory=ext disk=default, via migrate+trans online ext no off |+memory=ext disk=no, via migrate online ext int off | unsupported for now online ext ext off |*memory=ext disk=ext, via migrate+transaction * docs/schemas/domainsnapshot.rng (memory): New RNG element. * docs/formatsnapshot.html.in: Document it. * src/conf/snapshot_conf.h (virDomainSnapshotDef): New fields. * src/conf/domain_conf.c (virDomainSnapshotDefFree) (virDomainSnapshotDefParseString, virDomainSnapshotDefFormat): Manage new fields. * tests/domainsnapshotxml2xmltest.c: New test. * tests/domainsnapshotxml2xmlin/*.xml: Update existing tests. * tests/domainsnapshotxml2xmlout/*.xml: Likewise.
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>