> Am 12.06.2014 um 12:50 schrieb Greg Kurz <gk...@linux.vnet.ibm.com>:
>
> On Thu, 12 Jun 2014 12:39:27 +0200
> Alexander Graf <ag...@suse.de> wrote:
>
>>
>>
>>> Am 12.06.2014 um 12:14 schrieb Greg Kurz <gk...@linux.vnet.ibm.com>:
>>>
>>> On Thu, 12 Jun 2014 11:43:20 +0200
>>> Alexander Graf <ag...@suse.de> wrote:
>>>
>>>>
>>>>>> On 12.06.14 11:39, Paolo Bonzini wrote:
>>>>>> Il 12/06/2014 11:37, Michael S. Tsirkin ha scritto:
>>>>>> Maybe just drop unnecessary stuff for new machine types?
>>>>>> Then we won't need hacks to migrate it.
>>>>>
>>>>> For any machine type it's trivial to migrate it. All machine types
>>>>> including old ones can disregard the migrated values.
>>>>
>>>> How about a patch like this before the actual LE awareness ones? With
>>>> this we should make virtio-serial config space completely independent of
>>>> live migration.
>>>>
>>>> Also since QEMU versions that do read these swapped values during
>>>> migration are not bi-endian aware, we can never get into a case where a
>>>> cross-endian save needs to be considered ;).
>>>>
>>>>
>>>> Alex
>>>>
>>>>
>>>> diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
>>>> index 2b647b6..73cb9b7 100644
>>>> --- a/hw/char/virtio-serial-bus.c
>>>> +++ b/hw/char/virtio-serial-bus.c
>>>> @@ -670,6 +670,7 @@ static int virtio_serial_load(QEMUFile *f, void
>>>> *opaque, int version_id)
>>>> uint32_t max_nr_ports, nr_active_ports, ports_map;
>>>> unsigned int i;
>>>> int ret;
>>>> + uint32_t tmp;
>>>>
>>>> if (version_id > 3) {
>>>> return -EINVAL;
>>>> @@ -685,17 +686,12 @@ static int virtio_serial_load(QEMUFile *f, void
>>>> *opaque, int version_id)
>>>> return 0;
>>>> }
>>>>
>>>> - /* The config space */
>>>> - qemu_get_be16s(f, &s->config.cols);
>>>> - qemu_get_be16s(f, &s->config.rows);
>>>> -
>>>> - qemu_get_be32s(f, &max_nr_ports);
>>>> - tswap32s(&max_nr_ports);
>>>> - if (max_nr_ports > tswap32(s->config.max_nr_ports)) {
>>>> - /* Source could have had more ports than us. Fail migration. */
>>>> - return -EINVAL;
>>>> - }
>>>> + /* Unused */
>>>> + qemu_get_be16s(f, &tmp);
>>>> + qemu_get_be16s(f, &tmp);
>>>> + qemu_get_be32s(f, &tmp);
>>>>
>>>> + max_nr_ports = tswap32(s->config.max_nr_ports);
>>>> for (i = 0; i < (max_nr_ports + 31) / 32; i++) {
>>>> qemu_get_be32s(f, &ports_map);
>>>
>>> For the moment, we have 0 < max_nr_ports < 32 so the source
>>> machine only stores a single 32 bit value... If this limit
>>> gets raised, we can end up sending more than that... and
>>> only the source machine max_nr_ports value can give the
>>> information...
>>
>> Why? This value only ever gets set in realize, so it will not change during
>> the lifetime of the device - which means we don't need to migrate it.
>
> I agree with the fact that the value does not change and should not be
> migrated in the first place.
> I am just worried about the size of the active ports bitmap that is streamed
> in the for loop... it
> is only 32 bit as of today, because we are limited to 32 ports. How would
> this work if the limit is
> raised ? How can the destination machine know how many bits have to be read ?
The destination has be be executed in compat mode to the older qemu version via
a versioned machine type. This should ensure that limits are kept.
Alex
