[libvirt PATCH 54/80] qemu: Implement VIR_MIGRATE_POSTCOPY_RESUME for Begin phase

[Peter Krempa]

On Tue, May 10, 2022 at 17:21:15 +0200, Jiri Denemark wrote:
> Mostly we just need to check whether the domain is in a failed post-copy
> migration that can be resumed.
> 
> Signed-off-by: Jiri Denemark <jdenemar at redhat.com>
> ---
>  src/qemu/qemu_migration.c | 143 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 143 insertions(+)
> 
> diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
> index c111dd8686..99b1d4b88b 100644
> --- a/src/qemu/qemu_migration.c
> +++ b/src/qemu/qemu_migration.c
> @@ -2717,6 +2717,143 @@ qemuMigrationSrcBeginPhase(virQEMUDriver *driver,
>                                      flags);
>  }
>  
> +
> +static bool
> +qemuMigrationAnyCanResume(virDomainObj *vm,
> +                          virDomainAsyncJob job,
> +                          unsigned long flags,
> +                          qemuMigrationJobPhase expectedPhase)
> +{
> +    qemuDomainObjPrivate *priv = vm->privateData;
> +
> +    VIR_DEBUG("vm=%p, job=%s, flags=0x%lx, expectedPhase=%s",
> +              vm, virDomainAsyncJobTypeToString(job), flags,
> +              qemuDomainAsyncJobPhaseToString(VIR_ASYNC_JOB_MIGRATION_OUT,
> +                                              expectedPhase));
> +
> +    if (!(flags & VIR_MIGRATE_POSTCOPY)) {
> +        virReportError(VIR_ERR_ARGUMENT_UNSUPPORTED, "%s",
> +                       _("resuming failed post-copy migration requires "
> +                         "post-copy to be enabled"));

Error messages shall not have line breaks.

Also ... requiring this flag seems to be a bit pointless and ...
cosmetic at best. Since the previous migration would need to be started
with the post-copy flag already which is checked below.

> +        return false;
> +    }
> +
> +    /* This should never happen since POSTCOPY_RESUME is newer than
> +     * CHANGE_PROTECTION, but let's check it anyway in case we're talking to
> +     * a weired client.
> +     */
> +    if (job == VIR_ASYNC_JOB_MIGRATION_OUT &&
> +        expectedPhase < QEMU_MIGRATION_PHASE_PERFORM_RESUME &&
> +        !(flags & VIR_MIGRATE_CHANGE_PROTECTION)) {
> +        virReportError(VIR_ERR_ARGUMENT_UNSUPPORTED, "%s",
> +                       _("resuming failed post-copy migration requires "
> +                         "change protection"));

Same here.

> +        return NULL;
> +    }


[...]

> +static char *
> +qemuMigrationSrcBeginResume(virQEMUDriver *driver,
> +                            virDomainObj *vm,
> +                            const char *xmlin,
> +                            char **cookieout,
> +                            int *cookieoutlen,
> +                            unsigned long flags)
> +{
> +    virDomainJobStatus status;
> +
> +    if (qemuMigrationAnyRefreshStatus(driver, vm, VIR_ASYNC_JOB_MIGRATION_OUT,
> +                                      &status) < 0)
> +        return NULL;
> +
> +    if (status != VIR_DOMAIN_JOB_STATUS_POSTCOPY_PAUSED) {
> +        virReportError(VIR_ERR_OPERATION_INVALID, "%s",
> +                       _("QEMU reports migration is still running"));
> +        return NULL;
> +    }
> +
> +    return qemuMigrationSrcBeginXML(driver, vm, xmlin,
> +                                    cookieout, cookieoutlen, 0, NULL, 0, flags);

Certain steps here around the non-shared-storage migration are redundant
at this point and IMO should be skipped.

> +}
> +
> +
> +static char *
> +qemuMigrationSrcBeginResumePhase(virConnectPtr conn,
> +                                 virQEMUDriver *driver,
> +                                 virDomainObj *vm,
> +                                 const char *xmlin,
> +                                 char **cookieout,
> +                                 int *cookieoutlen,
> +                                 unsigned long flags)
> +{
> +    g_autofree char *xml = NULL;
> +
> +    VIR_DEBUG("vm=%p", vm);
> +
> +    if (!qemuMigrationAnyCanResume(vm, VIR_ASYNC_JOB_MIGRATION_OUT, flags,
> +                                   QEMU_MIGRATION_PHASE_POSTCOPY_FAILED))
> +        return NULL;
> +
> +    if (qemuMigrationJobStartPhase(vm, QEMU_MIGRATION_PHASE_BEGIN_RESUME) < 0)
> +        return NULL;
> +
> +    virCloseCallbacksUnset(driver->closeCallbacks, vm,
> +                           qemuMigrationSrcCleanup);
> +    qemuDomainCleanupRemove(vm, qemuProcessCleanupMigrationJob);

Could you please add an explanation why we are removing the callbacks
...

> +
> +    xml = qemuMigrationSrcBeginResume(driver, vm, xmlin, cookieout, cookieoutlen, flags);
> +
> +    if (virCloseCallbacksSet(driver->closeCallbacks, vm, conn,
> +                             qemuMigrationSrcCleanup) < 0)
> +        g_clear_pointer(&xml, g_free);
> +
> +    if (!xml)
> +        ignore_value(qemuMigrationJobSetPhase(vm, QEMU_MIGRATION_PHASE_POSTCOPY_FAILED));
> +
> +    qemuDomainCleanupAdd(vm, qemuProcessCleanupMigrationJob);

Just to add them here?

> +    qemuMigrationJobContinue(vm);
> +    return g_steal_pointer(&xml);
> +}