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Subject: Re: [PATCH 12/21] vhost-vdpa: introduce uAPI to get the number of
 virtqueue groups
To:     Eli Cohen <elic@nvidia.com>
Cc:     mst@redhat.com, eperezma@redhat.com, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, lulu@redhat.com, eli@mellanox.com,
        lingshan.zhu@intel.com, rob.miller@broadcom.com,
        stefanha@redhat.com, sgarzare@redhat.com
References: <20201216064818.48239-1-jasowang@redhat.com>
 <20201216064818.48239-13-jasowang@redhat.com>
 <20201229122455.GF195479@mtl-vdi-166.wap.labs.mlnx>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <f7e603f1-0200-566a-5360-f093da358b6d@redhat.com>
Date:   Wed, 30 Dec 2020 14:49:03 +0800
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On 2020/12/29 下午8:24, Eli Cohen wrote:
> On Wed, Dec 16, 2020 at 02:48:09PM +0800, Jason Wang wrote:
>> Follows the vDPA support for multiple address spaces, this patch
>> introduce uAPI for the userspace to know the number of virtqueue
>> groups supported by the vDPA device.
> Can you explain what exactly you mean be userspace?


It's the userspace that uses the uAPI introduced in this patch.


> Is it just qemu or
> is it destined to the virtio_net driver run by the qemu process?


It could be Qemu, DPDK or other userspace program.

The guest virtio-net driver will not use this but talks to the virtio 
device emulated by Qemu.


> Also can you say for what purpose?


This can be used for facilitate the checking of whether the control vq 
could be supported.

E.g if the device support less than 2 groups, qemu won't advertise 
control vq.

Yes, #groups could be inferred from GET_VRING_GROUP. But it's not 
straightforward as this.

Thanks


>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>>   drivers/vhost/vdpa.c       | 4 ++++
>>   include/uapi/linux/vhost.h | 3 +++
>>   2 files changed, 7 insertions(+)
>>
>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>> index 060d5b5b7e64..1ba5901b28e7 100644
>> --- a/drivers/vhost/vdpa.c
>> +++ b/drivers/vhost/vdpa.c
>> @@ -536,6 +536,10 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>>   	case VHOST_VDPA_GET_VRING_NUM:
>>   		r = vhost_vdpa_get_vring_num(v, argp);
>>   		break;
>> +	case VHOST_VDPA_GET_GROUP_NUM:
>> +		r = copy_to_user(argp, &v->vdpa->ngroups,
>> +				 sizeof(v->vdpa->ngroups));
>> +		break;
>>   	case VHOST_SET_LOG_BASE:
>>   	case VHOST_SET_LOG_FD:
>>   		r = -ENOIOCTLCMD;
>> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
>> index 59c6c0fbaba1..8a4e6e426bbf 100644
>> --- a/include/uapi/linux/vhost.h
>> +++ b/include/uapi/linux/vhost.h
>> @@ -145,4 +145,7 @@
>>   /* Get the valid iova range */
>>   #define VHOST_VDPA_GET_IOVA_RANGE	_IOR(VHOST_VIRTIO, 0x78, \
>>   					     struct vhost_vdpa_iova_range)
>> +/* Get the number of virtqueue groups. */
>> +#define VHOST_VDPA_GET_GROUP_NUM	_IOR(VHOST_VIRTIO, 0x79, unsigned int)
>> +
>>   #endif
>> -- 
>> 2.25.1
>>