Re: [PATCH v2 5/8] migration-test: Add COLO migration unit test

[Lukas Straub <lukasstraub2@web.de>]

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On Wed, 21 Jan 2026 20:37:51 +0100
Lukas Straub <lukasstraub2@web.de> wrote:

> On Tue, 20 Jan 2026 12:23:08 -0500
> Peter Xu <peterx@redhat.com> wrote:
> 
> > On Sat, Jan 17, 2026 at 03:09:12PM +0100, Lukas Straub wrote:  
> > > Add a COLO migration test for COLO migration and failover.
> > > 
> > > COLO does not support q35 machine at this time.
> > > 
> > > [...]
> > >  
> > > +int test_colo_common(MigrateCommon *args, bool failover_during_checkpoint,
> > > +                     bool primary_failover)
> > > +{
> > > +    QTestState *from, *to;
> > > +    void *data_hook = NULL;
> > > +
> > > +    /*
> > > +     * For the COLO test, both VMs will run in parallel. Thus both VMs want to
> > > +     * open the image read/write at the same time. Using read-only=on is not
> > > +     * possible here, because ide-hd does not support read-only backing image.
> > > +     *
> > > +     * So use -snapshot, where each qemu instance creates its own writable
> > > +     * snapshot internally while leaving the real image read-only.
> > > +     */
> > > +    args->start.opts_source = "-snapshot";
> > > +    args->start.opts_target = "-snapshot";
> > > +
> > > +    /*
> > > +     * COLO migration code logs many errors when the migration socket
> > > +     * is shut down, these are expected so we hide them here.
> > > +     */
> > > +    args->start.hide_stderr = true;
> > > +
> > > +    /*
> > > +     * COLO currently does not work with Q35 machine
> > > +     */
> > > +    args->start.force_pc_machine = true;
> > > +
> > > +    args->start.oob = true;    
> > 
> > Just curious: is OOB required in COLO for some reason?  I understand yank
> > you used below uses OOB, so the question is behind that, on what can be
> > blocked in main thread, and special in COLO.

There is a lot that can hang:
The netfilters all run on the main loop and use blocking write.
fiter-mirror on the primary side mirrors packets to the secondary and
can hang.
filter-redirect on the secondary side redirects packets to primary's
colo-compare and can hang.
The nbd client on the primary side that is connected to the nbd server
on the secondary side can hang. Especially during vm_stop() which fluses
all inflight block io with BQL held.

Regards,
Lukas Straub

> >   
> > > +    args->start.caps[MIGRATION_CAPABILITY_X_COLO] = true;
> > > +
> > > +    if (migrate_start(&from, &to, args->listen_uri, &args->start)) {
> > > +        return -1;
> > > +    }
> > > +
> > > +    migrate_set_parameter_int(from, "x-checkpoint-delay", 300);
> > > +
> > > +    if (args->start_hook) {
> > > +        data_hook = args->start_hook(from, to);
> > > +    }
> > > +
> > > +    migrate_ensure_converge(from);
> > > +    wait_for_serial("src_serial");
> > > +
> > > +    migrate_qmp(from, to, args->connect_uri, NULL, "{}");
> > > +
> > > +    wait_for_migration_status(from, "colo", NULL);
> > > +    wait_for_resume(to, &dst_state);    
> > 
> > We can move this whole function into colo-tests.c.  Here you may want to
> > use get_dst() instead.  
> 
> Okey, will do that.
> 
> >   
> > > +
> > > +    wait_for_serial("src_serial");
> > > +    wait_for_serial("dest_serial");
> > > +
> > > +    /* wait for 3 checkpoints */
> > > +    for (int i = 0; i < 3; i++) {
> > > +        qtest_qmp_eventwait(to, "RESUME");
> > > +        wait_for_serial("src_serial");
> > > +        wait_for_serial("dest_serial");
> > > +    }
> > > +
> > > +    if (failover_during_checkpoint) {
> > > +        qtest_qmp_eventwait(to, "STOP");
> > > +    }
> > > +    if (primary_failover) {
> > > +        qtest_qmp_assert_success(from, "{'exec-oob': 'yank', 'id': 'yank-cmd', "
> > > +                                            "'arguments': {'instances':"
> > > +                                                "[{'type': 'migration'}]}}");
> > > +        qtest_qmp_assert_success(from, "{'execute': 'x-colo-lost-heartbeat'}");
> > > +        wait_for_serial("src_serial");
> > > +    } else {
> > > +        qtest_qmp_assert_success(to, "{'exec-oob': 'yank', 'id': 'yank-cmd', "
> > > +                                        "'arguments': {'instances':"
> > > +                                            "[{'type': 'migration'}]}}");
> > > +        qtest_qmp_assert_success(to, "{'execute': 'x-colo-lost-heartbeat'}");
> > > +        wait_for_serial("dest_serial");
> > > +    }
> > > +
> > > +    if (args->end_hook) {
> > > +        args->end_hook(from, to, data_hook);
> > > +    }
> > > +
> > > +    migrate_end(from, to, !primary_failover);
> > > +
> > > +    return 0;
> > > +}
> > > +
> > >  QTestMigrationState *get_src(void)
> > >  {
> > >      return &src_state;
> > > [...]


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