Re: [Qemu-devel] [PATCH] vhost-vsock: support parse mergeable feature

[jiangyiwen <jiangyiwen@huawei.com>]

On 2018/12/12 21:19, Michael S. Tsirkin wrote:
> On Wed, Dec 12, 2018 at 05:54:49PM +0800, jiangyiwen wrote:
>> Currently vhost-vsock doesn't have any feature bits, so it
>> don't support parse mergeable rx buffer feature. And the
>> feature is support in another series of patches named
>> "VSOCK: support mergeable rx buffer in vhost-vsock".
>>
>> So we neet to support parse mergeable feature in vhost-vsock
>> if above patches are merged.
>>
>> Signed-off-by: Yiwen Jiang <jiangyiwen@huawei.com>
> 
> OK but what does it do? this just defines the feature bit ...
> Also pls copy virtio-dev whenever you change the host/guest
> interface.
> 
> Thanks!
> 

Hi Michael,

In my opinion, for vhost device, device feature bits need to be
intersected between vhost and qemu, so I add mergeable rx buffer feature
into vdev->host_features, and then intersected with vhost_dev features.

Later if someone want to add new feature, it can use virtio_add_feature()
in vhost_vsock_get_features().

Thanks,
Yiwen.

>> ---
>>  hw/virtio/vhost-vsock.c                       | 9 +++++++--
>>  include/standard-headers/linux/virtio_vsock.h | 3 +++
>>  2 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/virtio/vhost-vsock.c b/hw/virtio/vhost-vsock.c
>> index aa5af92..5023c05 100644
>> --- a/hw/virtio/vhost-vsock.c
>> +++ b/hw/virtio/vhost-vsock.c
>> @@ -178,8 +178,13 @@ static uint64_t vhost_vsock_get_features(VirtIODevice *vdev,
>>                                           uint64_t requested_features,
>>                                           Error **errp)
>>  {
>> -    /* No feature bits used yet */
>> -    return requested_features;
>> +    VHostVSock *vsock = VHOST_VSOCK(vdev);
>> +    uint64_t features;
>> +
>> +    virtio_add_feature(&requested_features, VIRTIO_VSOCK_F_MRG_RXBUF);
>> +    features = requested_features & vsock->vhost_dev.features;
>> +
>> +    return features;
>>  }
>>
>>  static void vhost_vsock_handle_output(VirtIODevice *vdev, VirtQueue *vq)
>> diff --git a/include/standard-headers/linux/virtio_vsock.h b/include/standard-headers/linux/virtio_vsock.h
>> index be44321..4c583ec 100644
>> --- a/include/standard-headers/linux/virtio_vsock.h
>> +++ b/include/standard-headers/linux/virtio_vsock.h
>> @@ -38,6 +38,9 @@
>>  #include "standard-headers/linux/virtio_ids.h"
>>  #include "standard-headers/linux/virtio_config.h"
>>
>> +/* Virtio-vsock feature */
>> +#define VIRTIO_VSOCK_F_MRG_RXBUF 0 /* Host can merge receive buffers. */
>> +
>>  struct virtio_vsock_config {
>>  	uint64_t guest_cid;
>>  } QEMU_PACKED;
>> -- 
>> 1.8.3.1
>>
> 
> .
>