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Subject: Re: [PATCH] vhost: introduce mdev based hardware backend
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     Tiwei Bie <tiwei.bie@intel.com>, alex.williamson@redhat.com,
        maxime.coquelin@redhat.com, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
        netdev@vger.kernel.org, dan.daly@intel.com,
        cunming.liang@intel.com, zhihong.wang@intel.com,
        lingshan.zhu@intel.com
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <a959fe1e-3095-e0f0-0c9b-57f6eaa9c8b7@redhat.com>
Date:   Fri, 27 Sep 2019 20:17:47 +0800
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On 2019/9/27 下午5:41, Michael S. Tsirkin wrote:
> On Fri, Sep 27, 2019 at 11:27:12AM +0800, Jason Wang wrote:
>> On 2019/9/26 下午9:14, Tiwei Bie wrote:
>>> On Thu, Sep 26, 2019 at 04:35:18AM -0400, Michael S. Tsirkin wrote:
>>>> On Thu, Sep 26, 2019 at 12:54:27PM +0800, Tiwei Bie wrote:
>>> [...]
>>>>> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
>>>>> index 40d028eed645..5afbc2f08fa3 100644
>>>>> --- a/include/uapi/linux/vhost.h
>>>>> +++ b/include/uapi/linux/vhost.h
>>>>> @@ -116,4 +116,12 @@
>>>>>    #define VHOST_VSOCK_SET_GUEST_CID	_IOW(VHOST_VIRTIO, 0x60, __u64)
>>>>>    #define VHOST_VSOCK_SET_RUNNING		_IOW(VHOST_VIRTIO, 0x61, int)
>>>>> +/* VHOST_MDEV specific defines */
>>>>> +
>>>>> +#define VHOST_MDEV_SET_STATE	_IOW(VHOST_VIRTIO, 0x70, __u64)
>>>>> +
>>>>> +#define VHOST_MDEV_S_STOPPED	0
>>>>> +#define VHOST_MDEV_S_RUNNING	1
>>>>> +#define VHOST_MDEV_S_MAX	2
>>>>> +
>>>>>    #endif
>>>> So assuming we have an underlying device that behaves like virtio:
>>> I think they are really good questions/suggestions. Thanks!
>>>
>>>> 1. Should we use SET_STATUS maybe?
>>> I like this idea. I will give it a try.
>>>
>>>> 2. Do we want a reset ioctl?
>>> I think it is helpful. If we use SET_STATUS, maybe we
>>> can use it to support the reset.
>>>
>>>> 3. Do we want ability to enable rings individually?
>>> I will make it possible at least in the vhost layer.
>>
>> Note the API support e.g set_vq_ready().
> virtio spec calls this "enabled" so let's stick to that.


Ok.


>
>>>> 4. Does device need to limit max ring size?
>>>> 5. Does device need to limit max number of queues?
>>> I think so. It's helpful to have ioctls to report the max
>>> ring size and max number of queues.
>>
>> An issue is the max number of queues is done through a device specific way,
>> usually device configuration space. This is supported by the transport API,
>> but how to expose it to userspace may need more thought.
>>
>> Thanks
> an ioctl for device config?  But for v1 I'd be quite happy to just have
> a minimal working device with 2 queues.


I'm fully agree, and it will work as long as VIRTIO_NET_F_MQ and 
VIRTIO_NET_F_CTRL_VQ is not advertised by the mdev device.

Thanks


>
>>> Thanks!