Re: [libvirt] [PATCH] qemu: Don't set migration caps when changing postcopy bandwidth

On Wed, Mar 06, 2019 at 12:39:56 +0100, Peter Krempa wrote: > On Wed, Mar 06, 2019 at 12:15:08 +0100, Jiri Denemark wrote:

So how about: The qemuMigrationParamsApply internal API was designed to apply all migration parameters and capabilities before we start to migrate a domain. While migration parameters are only passed to QEMU when we explicitly want to set a specific value, capabilities are always either enabled or disabled. Thus when this API is called outside migration job, e.g., via a call to qemuDomainMigrateSetMaxSpeed with VIR_DOMAIN_MIGRATE_MAX_SPEED_POSTCOPY flag, we would call migrate-set-capabilities and disable all capabilities. However, changing capabilities while migration is already running does not make sense and our code should never be trying to do so. In fact QEMU even reports an error if migrate-set-capabilities is called during migration and qemuDomainMigrateSetMaxSpeed would fail with: internal error: unable to execute QEMU command migrate-set-capabilities: There's a migration process in progress With this patch qemuMigrationParamsApply never tries to call migrate-set-capabilities outside of migration job. When the capabilities bitmap is all zeros (which is its initial value after qemuMigrationParamsNew), we just skip the command. But when any capability bit is set to 1 by a non-migration job, we report an error to highlight a bug in our code.