Virtualization - Feb 2022 - [PATCH 16/31] vhost: pass queue index to vhost_vq_get_addr

? 2022/2/1 ??1:44, Eugenio Perez Martin ??:
> On Sat, Jan 29, 2022 at 9:20 AM Jason Wang <jasowang at redhat.com>
wrote:
>>
>> ? 2022/1/22 ??4:27, Eugenio P?rez ??:
>>> Doing that way allows vhost backend to know what address to return.
>>>
>>> Signed-off-by: Eugenio P?rez <eperezma at redhat.com>
>>> ---
>>>    hw/virtio/vhost.c | 6 +++---
>>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
>>> index 7b03efccec..64b955ba0c 100644
>>> --- a/hw/virtio/vhost.c
>>> +++ b/hw/virtio/vhost.c
>>> @@ -798,9 +798,10 @@ static int vhost_virtqueue_set_addr(struct
vhost_dev *dev,
>>>                                        struct vhost_virtqueue *vq,
>>>                                        unsigned idx, bool
enable_log)
>>>    {
>>> -    struct vhost_vring_addr addr;
>>> +    struct vhost_vring_addr addr = {
>>> +        .index = idx,
>>> +    };
>>>        int r;
>>> -    memset(&addr, 0, sizeof(struct vhost_vring_addr));
>>>
>>>        if (dev->vhost_ops->vhost_vq_get_addr) {
>>>            r = dev->vhost_ops->vhost_vq_get_addr(dev,
&addr, vq);
>>> @@ -813,7 +814,6 @@ static int vhost_virtqueue_set_addr(struct
vhost_dev *dev,
>>>            addr.avail_user_addr = (uint64_t)(unsigned
long)vq->avail;
>>>            addr.used_user_addr = (uint64_t)(unsigned
long)vq->used;
>>>        }
>>
>> I'm a bit lost in the logic above, any reason we need call
>> vhost_vq_get_addr() :) ?
>>
> It's the way vhost_virtqueue_set_addr works if the backend has a
> vhost_vq_get_addr operation (currently, only vhost-vdpa). vhost first
> ask the address to the back end and then set it.

Right it's because vhost-vdpa doesn't use VA but GPA. But I'm not
sure
it's worth a dedicated vhost_ops. But consider we introduce shadow 
virtqueue stuffs, it should be ok now.

(In the future, we may consider to generalize non vhost-vdpa specific 
stuffs to VhostShadowVirtqueue, then we can get rid of this vhost_ops.

>
> Previously, index was not needed because all the information was in
> vhost_virtqueue. However to extract queue index from vhost_virtqueue
> is tricky, so I think it's easier to simply have that information at
> request, something similar to get_base or get_num when asking vdpa
> device. We can extract the index from vq - dev->vqs or something
> similar if it's prefered.

It looks odd for the caller to tell the index consider vhost_virtqueue 
is already passed. So I think we need deduce it from vhost_virtqueue as 
you mentioned here.

Thanks

>
> Thanks!
>
>> Thanks
>>
>>
>>> -    addr.index = idx;
>>>        addr.log_guest_addr = vq->used_phys;
>>>        addr.flags = enable_log ? (1 << VHOST_VRING_F_LOG) :
0;
>>>        r = dev->vhost_ops->vhost_set_vring_addr(dev,
&addr);