Re: [PATCH RFC] migration: warn about non-migratable configurations unless '--no-migration' was specified

[Markus Armbruster <armbru@redhat.com>]

Markus Armbruster <armbru@redhat.com> writes:

[...]

> Apropos blocked-reasons.  migration.json has:
>
>     # @blocked: True if outgoing migration is blocked (since 6.0)
>     #
>     # @blocked-reasons: A list of reasons an outgoing migration is blocked (since 6.0)
>     [...]
>               'blocked': 'bool',
>               '*blocked-reasons': ['str'],
>
> Can "blocked-reasons" be absent or empty when "blocked" is true?

No.

From fill_source_migration_info():

        info->blocked = migration_is_blocked(NULL);
        info->has_blocked_reasons = info->blocked;
        info->blocked_reasons = NULL;
        if (info->blocked) {
            GSList *cur_blocker = migration_blockers;

            /*
             * There are two types of reasons a migration might be blocked;
             * a) devices marked in VMState as non-migratable, and
             * b) Explicit migration blockers
             * We need to add both of them here.
             */
            qemu_savevm_non_migratable_list(&info->blocked_reasons);

            while (cur_blocker) {
                QAPI_LIST_PREPEND(info->blocked_reasons,
                                  g_strdup(error_get_pretty(cur_blocker->data)));
                cur_blocker = g_slist_next(cur_blocker);
            }
        }

where

    bool migration_is_blocked(Error **errp)
    {
        if (qemu_savevm_state_blocked(errp)) {
            return true;
        }

        if (migration_blockers) {
            error_propagate(errp, error_copy(migration_blockers->data));
            return true;
        }

        return false;
    }

and

    bool qemu_savevm_state_blocked(Error **errp)
    {
        SaveStateEntry *se;

        QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
            if (se->vmsd && se->vmsd->unmigratable) {
                error_setg(errp, "State blocked by non-migratable device '%s'",
                           se->idstr);
                return true;
            }
        }
        return false;
    }

    void qemu_savevm_non_migratable_list(strList **reasons)
    {
        SaveStateEntry *se;

        QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
            if (se->vmsd && se->vmsd->unmigratable) {
                QAPI_LIST_PREPEND(*reasons,
                                  g_strdup_printf("non-migratable device: %s",
                                                  se->idstr));
            }
        }
    }

info->blocked is "non-migratable devices exist, or migration blockers
exist".

info->blocked_reasons has one entry per non-migratable device, and one
entry per migration blocker.

> If not, then "blocked" is redundant, and should be dropped before we
> release 6.0.

It is, and it should.

> Else, the documentation should spell it out.  No need to rush that.
>
> The patch was not cc'ed to me.  I might have caught it earlier...

"The patch" is commit 3af8554bd0 "migration: Add blocker information"

>
> [...]