Re: [Qemu-devel] [PATCH] virtio: enhance virtio_error messages

[Stefan Hajnoczi]

On Wed, Jul 12, 2017 at 10:05:38AM +0200, Ladi Prosek wrote:
> Output like "Virtqueue size exceeded" is not much useful in identifying the
> culprit. This commit adds virtio device name and queue index to all error
> messages in virtio.c to improve debuggability.
> 
> Signed-off-by: Ladi Prosek <address@hidden>
> ---
>  hw/virtio/virtio.c | 74 
> +++++++++++++++++++++++++++++++++---------------------
>  1 file changed, 46 insertions(+), 28 deletions(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 464947f..5040f26 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -143,7 +143,7 @@ static void virtio_init_region_cache(VirtIODevice *vdev, 
> int n)
>      len = address_space_cache_init(&new->desc, vdev->dma_as,
>                                     addr, size, false);
>      if (len < size) {
> -        virtio_error(vdev, "Cannot map desc");
> +        virtio_error(vdev, "%s queue %u: Cannot map desc", vdev->name, n);

Good idea!

Please build the identifying information into virtio_error() to avoid
code duplication.

It probably makes sense to add a virtqueue_error(VirtIOQueue *vq, fmt,
...) function.  That way the virtqueue number printing doesn't need to
be duplicated.

vdev->name specifies the device type ("virtio-net", "virtio-9p") but
does not uniquely identify the device instance.  If a guest has multiple
virtio-net devices then the error message will not identify the device
instance.  I think you can use DEVICE(vdev)->id instead to get the
unique -device virtio-net-pci,id=vnet0 identifier.

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