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Migration is another case of stranding metadata. And since snapshot metadata is arbitrarily large, there's no way to shoehorn it into the migration cookie of migration v3. This patch consolidates two existing locations for migration validation into one helper function, then enhances that function to also do the new checks. If we could always trust the source to validate migration, then the destination would not have to do anything; but since older servers that did not do checking can migrate to newer destinations, we have to repeat some of the same checks on the destination; meanwhile, we want to detect failures as soon as possible. With migration v2, this means that validation will reject things at Prepare on the destination if the XML exposes the problem, otherwise at Perform on the source; with migration v3, this means that validation will reject things at Begin on the source, or if the source is old and the XML exposes the problem, then at Prepare on the destination. This patch is necessarily over-strict. Once a later patch properly handles auto-cleanup of snapshot metadata on the death of a transient domain, then the only time we actually need snapshots to prevent migration is when using the --undefinesource flag on a persistent source domain. It is possible to recreate snapshot metadata on the destination with VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE and VIR_DOMAIN_SNAPSHOT_CREATE_CURRENT. But for now, that is limited, since if we delete the snapshot metadata prior to migration, then we won't know the name of the current snapshot to pass along; and if we delete the snapshot metadata after migration and use the v3 migration cookie to pass along the name of the current snapshot, then we need a way to bypass the fact that this patch refuses migration with snapshot metadata present. So eventually, we may have to introduce migration protocol v4 that allows feature negotiation and an arbitrary number of handshake exchanges, so as to pass as many rpc calls as needed to transfer all the snapshot xml hierarchy. But all of that is thoughts for the future; for now, the best course of action is to quit early, rather than get into a funky state of stale metadata; then relax restrictions later. * src/qemu/qemu_migration.h (qemuMigrationIsAllowed): Make static. * src/qemu/qemu_migration.c (qemuMigrationIsAllowed): Alter signature, and allow checks for both outgoing and incoming. (qemuMigrationBegin, qemuMigrationPrepareAny) (qemuMigrationPerformJob): Update callers.
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>