Re: [PATCH v3 2/8] vdpa: Use iovec for vhost_vdpa_net_cvq_add()

[Hawkins Jiawei <yin31149@gmail.com>]

On 2023/8/18 23:23, Eugenio Perez Martin wrote:
> On Wed, Jul 19, 2023 at 9:54 AM Hawkins Jiawei <yin31149@gmail.com> wrote:
>>
>> Next patches in this series will no longer perform an
>> immediate poll and check of the device's used buffers
>> for each CVQ state load command. Consequently, there
>> will be multiple pending buffers in the shadow VirtQueue,
>> making it a must for every control command to have its
>> own buffer.
>>
>> To achieve this, this patch refactor vhost_vdpa_net_cvq_add()
>> to accept `struct iovec`, which eliminates the coupling of
>> control commands to `s->cvq_cmd_out_buffer` and `s->status`,
>> allowing them to use their own buffer.
>>
>> Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
>> ---
>>   net/vhost-vdpa.c | 38 ++++++++++++++++++++------------------
>>   1 file changed, 20 insertions(+), 18 deletions(-)
>>
>> diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
>> index d1dd140bf6..6b16c8ece0 100644
>> --- a/net/vhost-vdpa.c
>> +++ b/net/vhost-vdpa.c
>> @@ -596,22 +596,14 @@ static void vhost_vdpa_net_cvq_stop(NetClientState *nc)
>>       vhost_vdpa_net_client_stop(nc);
>>   }
>>
>> -static ssize_t vhost_vdpa_net_cvq_add(VhostVDPAState *s, size_t out_len,
>> -                                      size_t in_len)
>> +static ssize_t vhost_vdpa_net_cvq_add(VhostVDPAState *s,
>> +                                      struct iovec *out_sg, size_t out_num,
>> +                                      struct iovec *in_sg, size_t in_num)
>>   {
>> -    /* Buffers for the device */
>> -    const struct iovec out = {
>> -        .iov_base = s->cvq_cmd_out_buffer,
>> -        .iov_len = out_len,
>> -    };
>> -    const struct iovec in = {
>> -        .iov_base = s->status,
>> -        .iov_len = sizeof(virtio_net_ctrl_ack),
>> -    };
>>       VhostShadowVirtqueue *svq = g_ptr_array_index(s->vhost_vdpa.shadow_vqs, 0);
>>       int r;
>>
>> -    r = vhost_svq_add(svq, &out, 1, &in, 1, NULL);
>> +    r = vhost_svq_add(svq, out_sg, out_num, in_sg, in_num, NULL);
>>       if (unlikely(r != 0)) {
>>           if (unlikely(r == -ENOSPC)) {
>>               qemu_log_mask(LOG_GUEST_ERROR, "%s: No space on device queue\n",
>> @@ -637,6 +629,15 @@ static ssize_t vhost_vdpa_net_load_cmd(VhostVDPAState *s, uint8_t class,
>>           .cmd = cmd,
>>       };
>>       size_t data_size = iov_size(data_sg, data_num);
>> +    /* Buffers for the device */
>> +    struct iovec out = {
>> +        .iov_base = s->cvq_cmd_out_buffer,
>> +        .iov_len = sizeof(ctrl) + data_size,
>> +    };
>> +    struct iovec in = {
>> +        .iov_base = s->status,
>> +        .iov_len = sizeof(*s->status),
>> +    };
>>
>>       assert(data_size < vhost_vdpa_net_cvq_cmd_page_len() - sizeof(ctrl));
>>
>> @@ -647,8 +648,7 @@ static ssize_t vhost_vdpa_net_load_cmd(VhostVDPAState *s, uint8_t class,
>>       iov_to_buf(data_sg, data_num, 0,
>>                  s->cvq_cmd_out_buffer + sizeof(ctrl), data_size);
>>
>> -    return vhost_vdpa_net_cvq_add(s, data_size + sizeof(ctrl),
>> -                                  sizeof(virtio_net_ctrl_ack));
>> +    return vhost_vdpa_net_cvq_add(s, &out, 1, &in, 1);
>>   }
>>
>>   static int vhost_vdpa_net_load_mac(VhostVDPAState *s, const VirtIONet *n)
>> @@ -1222,9 +1222,7 @@ static int vhost_vdpa_net_handle_ctrl_avail(VhostShadowVirtqueue *svq,
>>       struct iovec out = {
>>           .iov_base = s->cvq_cmd_out_buffer,
>>       };
>> -    /* in buffer used for device model */
>> -    const struct iovec in = {
>> -        .iov_base = &status,
>> +    struct iovec in = {
>
> What if instead of reusing "in" we declare a new struct iovec in the
> condition that calls vhost_vdpa_net_cvq_add? Something in the line of
> "device_in".
>
> I'm also ok with this code, but splitting them would reduce the
> possibility of sending the wrong one to the device / virtio device
> model by mistake.

Hi Eugenio,

Ok, I will refactor this part of code according to your suggestion in
the v4 patch.

Thanks!


>
> Thanks!
>
>>           .iov_len = sizeof(status),
>>       };
>>       ssize_t dev_written = -EINVAL;
>> @@ -1232,6 +1230,8 @@ static int vhost_vdpa_net_handle_ctrl_avail(VhostShadowVirtqueue *svq,
>>       out.iov_len = iov_to_buf(elem->out_sg, elem->out_num, 0,
>>                                s->cvq_cmd_out_buffer,
>>                                vhost_vdpa_net_cvq_cmd_page_len());
>> +    /* In buffer used for the vdpa device */
>> +    in.iov_base = s->status;
>>
>>       ctrl = s->cvq_cmd_out_buffer;
>>       if (ctrl->class == VIRTIO_NET_CTRL_ANNOUNCE) {
>> @@ -1260,7 +1260,7 @@ static int vhost_vdpa_net_handle_ctrl_avail(VhostShadowVirtqueue *svq,
>>               goto out;
>>           }
>>       } else {
>> -        dev_written = vhost_vdpa_net_cvq_add(s, out.iov_len, sizeof(status));
>> +        dev_written = vhost_vdpa_net_cvq_add(s, &out, 1, &in, 1);
>>           if (unlikely(dev_written < 0)) {
>>               goto out;
>>           }
>> @@ -1276,6 +1276,8 @@ static int vhost_vdpa_net_handle_ctrl_avail(VhostShadowVirtqueue *svq,
>>       }
>>
>>       status = VIRTIO_NET_ERR;
>> +    /* In buffer used for the device model */
>> +    in.iov_base = &status;
>>       virtio_net_handle_ctrl_iov(svq->vdev, &in, 1, &out, 1);
>>       if (status != VIRTIO_NET_OK) {
>>           error_report("Bad CVQ processing in model");
>> --
>> 2.25.1
>>
>