Re: [Qemu-devel] [Qemu-block] Guest unresponsive after Virtqueue size exceeded error

[Stefan Hajnoczi <stefanha@gmail.com>]

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Are you sure this happens with both virtio-blk and virtio-scsi?

The following patch adds more debug output.  You can build as follows:

  $ git clone https://git.qemu.org/git/qemu.git
  $ cd qemu
  $ patch apply -p1
  ...paste the patch here...
  ^D

  # For info on build dependencies see https://wiki.qemu.org/Hosts/Linux
  $ ./configure --target-list=x86_64-softmmu
  $ make -j4

You can configure a libvirt domain to use your custom QEMU binary by
changing the <devices><emulator> tag to the
qemu/x86_64-softmmu/qemu-system-x86_64 path.

---

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 22bd1ac34e..aa44bffa1f 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -879,6 +879,9 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz)
     max = vq->vring.num;

     if (vq->inuse >= vq->vring.num) {
+        fprintf(stderr, "vdev %p (\"%s\")\n", vdev, vdev->name);
+        fprintf(stderr, "vq %p (idx %u)\n", vq, (unsigned int)(vq - vdev->vq));
+        fprintf(stderr, "inuse %u vring.num %u\n", vq->inuse, vq->vring.num);
         virtio_error(vdev, "Virtqueue size exceeded");
         goto done;
     }


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