Re: [dpdk-dev] [PATCH v2 4/7] vhost: translate iovas at vectors fill time

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 06/25/2018 12:31 PM, Tiwei Bie wrote:
> On Mon, Jun 25, 2018 at 09:19:34AM +0200, Maxime Coquelin wrote:
>> On 06/25/2018 04:21 AM, Tiwei Bie wrote:
>>> On Sat, Jun 23, 2018 at 09:11:24AM +0200, Maxime Coquelin wrote:
> [...]
>>>> @@ -293,7 +314,8 @@ fill_vec_buf(struct virtio_net *dev, struct vhost_virtqueue *vq,
>>>>    static inline int
>>>>    reserve_avail_buf(struct virtio_net *dev, struct vhost_virtqueue *vq,
>>>>    				uint32_t size, struct buf_vector *buf_vec,
>>>> -				uint16_t *num_buffers, uint16_t avail_head)
>>>> +				uint16_t *num_buffers, uint16_t avail_head,
>>>> +				uint16_t *nr_vec)
>>>>    {
>>>>    	uint16_t cur_idx;
>>>>    	uint32_t vec_idx = 0;
>>>> @@ -315,7 +337,8 @@ reserve_avail_buf(struct virtio_net *dev, struct vhost_virtqueue *vq,
>>>>    			return -1;
>>>>    		if (unlikely(fill_vec_buf(dev, vq, cur_idx, &vec_idx, buf_vec,
>>>> -						&head_idx, &len) < 0))
>>>> +						&head_idx, &len,
>>>> +						VHOST_ACCESS_RO) < 0))
>>>
>>> reserve_avail_buf() is called by virtio_dev_rx(),
>>> so the write perm is needed.
>> Right.
>>
>> To avoid having to pass the perms, I wonder if it wouldn't be better to
>> rely on the descriptors' VRING_DESC_F_WRITE flag.
>>
> 
> Currently, DPDK vhost net doesn't check this flag,
> so it could cause problems in some cases. If we
> want to rely on this flag, I think we still need
> to pass something similar to tell fill_vec_buf()
> whether the bufs will be written or read, so the
> flag can be checked.

Right, let's keep the perm parameter for now.

Thanks,
Maxime

> Best regards,
> Tiwei Bie
>