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Date: Thu, 12 Feb 2015 15:52:22 +0200
From: Vasile Catalin-B50542 <catalin.vasile@freescale.com>
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Subject: [Qemu-devel] [virtio] virtqueue request size
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To: qemu-devel@nongnu.org

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;