Re: [Qemu-devel] [PATCH v2 1/2] virtio: Add function to check whether backend supports VIRTIO_1

[Marcel Apfelbaum <marcel@redhat.com>]

On 09/09/2016 08:47 PM, Michael S. Tsirkin wrote:
> On Fri, Sep 09, 2016 at 08:00:31PM +0300, Marcel Apfelbaum wrote:
>> On 09/09/2016 04:10 PM, Maxime Coquelin wrote:
>>> This patch adds virtio_test_backend_virtio_1() function to
>>> check whether backend supports VIRTIO_F_VERSION_1 before the
>>> negociation takes place.
>>>
>>> Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
>>> Cc: Marcel Apfelbaum <marcel@redhat.com>
>>> Cc: Michael S. Tsirkin <mst@redhat.com>
>>> Cc: qemu-stable@nongnu.org
>>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>>> ---
>>>  hw/virtio/virtio.c         | 13 +++++++++++++
>>>  include/hw/virtio/virtio.h |  1 +
>>>  2 files changed, 14 insertions(+)
>>>
>>> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
>>> index 74c085c..8b30b69 100644
>>> --- a/hw/virtio/virtio.c
>>> +++ b/hw/virtio/virtio.c
>>> @@ -1481,6 +1481,19 @@ void virtio_vmstate_save(QEMUFile *f, void *opaque, size_t size)
>>>      virtio_save(VIRTIO_DEVICE(opaque), f);
>>>  }
>>>
>>> +bool virtio_test_backend_virtio_1(VirtIODevice *vdev, Error **errp)
>>> +{
>>> +    VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
>>> +    uint64_t feature;
>>> +
>>
>> I would set "feature = 0" even if doesn't really matter.
>> Anyway:
>>
>> Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
>>
>> Thanks,
>> Marcel
>
> why wouldn't it matter? Looks like an uninitialized variable to me.

because it adds a flag, then it checks only if this specific flag is
negotiated, but uninitialized variables are never a good idea.

Thanks,
Marcel

>
>>> +    virtio_add_feature(&feature, VIRTIO_F_VERSION_1);
>>> +
>>> +    assert(k->get_features != NULL);
>>> +    feature = k->get_features(vdev, feature, errp);
>>> +
>>> +    return virtio_has_feature(feature, VIRTIO_F_VERSION_1);
>>> +}
>>> +
>>>  static int virtio_set_features_nocheck(VirtIODevice *vdev, uint64_t val)
>>>  {
>>>      VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
>>> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
>>> index d2490c1..3a31754 100644
>>> --- a/include/hw/virtio/virtio.h
>>> +++ b/include/hw/virtio/virtio.h
>>> @@ -235,6 +235,7 @@ int virtio_set_status(VirtIODevice *vdev, uint8_t val);
>>>  void virtio_reset(void *opaque);
>>>  void virtio_update_irq(VirtIODevice *vdev);
>>>  int virtio_set_features(VirtIODevice *vdev, uint64_t val);
>>> +bool virtio_test_backend_virtio_1(VirtIODevice *vdev, Error **errp);
>>>
>>>  /* Base devices.  */
>>>  typedef struct VirtIOBlkConf VirtIOBlkConf;
>>>