[Qemu-devel] [virtio] virtqueue request size

[Qemu-devel] [virtio] virtqueue request size

[Vasile Catalin-B50542]

I'm trying to work out virtqueue from the virtio API.
I've been able to send a message from guest to qemu, but there is something
strange that I don't understand.
virtqueue_get_avail_bytes() returns 0 number of "in" bytes, but if I 
hard code
iov_to_buf() to get 5 bytes, it actually gets my message.
What am I missing out?

Here is the essential code so far:
Guest:
     probe function:
         vq = virtio_find_single_vq(vdev, recv_done, "input");
     triggered send function:
         sg_init_one(&sg, buf, size);
         if (virtqueue_add_inbuf(vq, &sg, 1, buf, GFP_KERNEL) < 0)
             BUG();
         virtqueue_kick(vq);

Qemu:
     realize function:
         vcrypto->vq = virtio_add_queue(vdev, 8, handle_input);
     handle_input:
         virtqueue_pop(vcrypto->vq, &elem);
         eprintf("request size is %u", get_request_size(vcrypto->vq, 
100)); // prints size 0
         iov_to_buf(elem.in_sg, elem.in_num, 0, buffer, 5); // hardcoded 
to 5 bytes for now
     get_request_size:
         virtqueue_get_avail_bytes(vq, &in, &out, quota, quota); // 
quota = 100
         return in;

Re: [Qemu-devel] [virtio] virtqueue request size

[Vasile Catalin-B50542]

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I found what was the problem.
virtqueue_get_avail_bytes() must be called before  virtqueue_pop().


On 12.02.2015 15:52, Vasile Catalin-B50542 wrote:
> I'm trying to work out virtqueue from the virtio API.
> I've been able to send a message from guest to qemu, but there is 
> something
> strange that I don't understand.
> virtqueue_get_avail_bytes() returns 0 number of "in" bytes, but if I 
> hard code
> iov_to_buf() to get 5 bytes, it actually gets my message.
> What am I missing out?
>
> Here is the essential code so far:
> Guest:
>     probe function:
>         vq = virtio_find_single_vq(vdev, recv_done, "input");
>     triggered send function:
>         sg_init_one(&sg, buf, size);
>         if (virtqueue_add_inbuf(vq, &sg, 1, buf, GFP_KERNEL) < 0)
>             BUG();
>         virtqueue_kick(vq);
>
> Qemu:
>     realize function:
>         vcrypto->vq = virtio_add_queue(vdev, 8, handle_input);
>     handle_input:
>         virtqueue_pop(vcrypto->vq, &elem);
>         eprintf("request size is %u", get_request_size(vcrypto->vq, 
> 100)); // prints size 0
>         iov_to_buf(elem.in_sg, elem.in_num, 0, buffer, 5); // 
> hardcoded to 5 bytes for now
>     get_request_size:
>         virtqueue_get_avail_bytes(vq, &in, &out, quota, quota); // 
> quota = 100
>         return in;

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Re: [Qemu-devel] [virtio] virtqueue request size

[Vasile Catalin-B50542]

I found out what was the problem.
I was calling virtqueue_get_avail_bytes() after virtqueue_pop().

On 12.02.2015 15:52, Vasile Catalin-B50542 wrote:
> I'm trying to work out virtqueue from the virtio API.
> I've been able to send a message from guest to qemu, but there is 
> something
> strange that I don't understand.
> virtqueue_get_avail_bytes() returns 0 number of "in" bytes, but if I 
> hard code
> iov_to_buf() to get 5 bytes, it actually gets my message.
> What am I missing out?
>
> Here is the essential code so far:
> Guest:
>     probe function:
>         vq = virtio_find_single_vq(vdev, recv_done, "input");
>     triggered send function:
>         sg_init_one(&sg, buf, size);
>         if (virtqueue_add_inbuf(vq, &sg, 1, buf, GFP_KERNEL) < 0)
>             BUG();
>         virtqueue_kick(vq);
>
> Qemu:
>     realize function:
>         vcrypto->vq = virtio_add_queue(vdev, 8, handle_input);
>     handle_input:
>         virtqueue_pop(vcrypto->vq, &elem);
>         eprintf("request size is %u", get_request_size(vcrypto->vq, 
> 100)); // prints size 0
>         iov_to_buf(elem.in_sg, elem.in_num, 0, buffer, 5); // 
> hardcoded to 5 bytes for now
>     get_request_size:
>         virtqueue_get_avail_bytes(vq, &in, &out, quota, quota); // 
> quota = 100
>         return in;