Re: [Qemu-devel] [PATCH] virtio-net: require that config size is initialized

["KONRAD Frédéric" <fred.konrad@greensocs.com>]

On 07/05/2013 14:33, Michael S. Tsirkin wrote:
> On Tue, May 07, 2013 at 02:29:38PM +0200, KONRAD Frédéric wrote:
>> Hi,
>>
>> I think it is not a good idea, as we wanted to make VirtIODevice
>> hot-pluggable for virtio-mmio.
> And then this hack will break cross version migration.

Why?

virtio_net_set_config_size is called by each "proxy" devices no?

>
>> Maybe we can use a callback which is called by virtio-bus before
>> plugging, to ensure that this
>> config size is computed?
> OK, will you post such a patch?
>

The issue is as we said in the last thread, host_feature is part of the 
proxy.

And if we want to move it to the devices, we must have a kind of 
property forwarding mechanism.

Anthony said he had something about that.

>> On 07/05/2013 12:22, Michael S. Tsirkin wrote:
>>> All buses do this, and if they don't they get subtle
>>> bugs related to cross version migration.
>>> Let's add an assert to catch these bugs early.
>>>
>>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>>> ---
>>>
>>> Just a cleanup so not 1.5 material.
>>> Seems to work fine here - any opinions?
>>>
>>>   hw/net/virtio-net.c | 7 ++++---
>>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>>> index 908e7b8..f0a9272 100644
>>> --- a/hw/net/virtio-net.c
>>> +++ b/hw/net/virtio-net.c
>>> @@ -1282,6 +1282,8 @@ static int virtio_net_device_init(VirtIODevice *vdev)
>>>       DeviceState *qdev = DEVICE(vdev);
>>>       VirtIONet *n = VIRTIO_NET(vdev);
>>> +    /* Verify that config size has been initialized */
>>> +    assert(n->config_size != (size_t)-1);
>>>       virtio_init(VIRTIO_DEVICE(n), "virtio-net", VIRTIO_ID_NET,
>>>                                     n->config_size);
>>> @@ -1386,10 +1388,9 @@ static void virtio_net_instance_init(Object *obj)
>>>       VirtIONet *n = VIRTIO_NET(obj);
>>>       /*
>>> -     * The default config_size is sizeof(struct virtio_net_config).
>>> -     * Can be overriden with virtio_net_set_config_size.
>>> +     * The config_size must be set later with virtio_net_set_config_size.
>>>        */
>>> -    n->config_size = sizeof(struct virtio_net_config);
>>> +    n->config_size = (size_t)-1;
>>>   }
>>>   static Property virtio_net_properties[] = {