Re: [Qemu-devel] [QEMU PATCH v10 2/3] migration: migrate QTAILQ

[Jianjun Duan]

On 11/02/2016 03:45 AM, Juan Quintela wrote:
> Jianjun Duan <address@hidden> wrote:
>> Currently we cannot directly transfer a QTAILQ instance because of the
>> limitation in the migration code. Here we introduce an approach to
>> transfer such structures. We created VMStateInfo vmstate_info_qtailq
>> for QTAILQ. Similar VMStateInfo can be created for other data structures
>> such as list.
>>
>> This approach will be used to transfer pending_events and ccs_list in spapr
>> state.
>>
>> We also create some macros in qemu/queue.h to access a QTAILQ using pointer
>> arithmetic. This ensures that we do not depend on the implementation
>> details about QTAILQ in the migration code.
>>
>> Signed-off-by: Jianjun Duan <address@hidden>
> 
> 
>> +
>> +    trace_get_qtailq(vmsd->name, version_id);
>> +    if (version_id > vmsd->version_id) {
>> +        error_report("%s %s",  vmsd->name, "too new");
>> +        trace_get_qtailq_end(vmsd->name, "too new", -EINVAL);
>> +
>> +        return -EINVAL;
>> +    }
>> +    if (version_id < vmsd->minimum_version_id) {
>> +        error_report("%s %s",  vmsd->name, "too old");
>> +        trace_get_qtailq_end(vmsd->name, "too old", -EINVAL);
>> +        return -EINVAL;
>> +    }
>> +
>> +    while (qemu_get_byte(f)) {
>> +        elm = g_malloc(size);
> 
> I think this is not generic enough.  We really need to allocate a new
> element, and then fill it with default values.
> 
> virtio list code use it in this way.
> 
> 
To do that we need probably to expand VMStateDescription and/or
VMStateField so that a default value can be supplied. Or we can always
fill the untouched fields in post_load.

Thanks,
Jianjun

> Thanks, Juan.
>