Re: [PATCH v2] virtio: add VIRTQUEUE_ERROR QAPI event

[Markus Armbruster <armbru@redhat.com>]

Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes:

> For now we only log the vhost device error, when virtqueue is actually
> stopped. Let's add a QAPI event, which makes possible:
>
>  - collect statistics of such errors
>  - make immediate actions: take core dumps or do some other debugging
>  - inform the user through a management API or UI, so that (s)he can
>   react somehow, e.g. reset the device driver in the guest or even
>   build up some automation to do so
>
> Note that basically every inconsistency discovered during virtqueue
> processing results in a silent virtqueue stop.  The guest then just
> sees the requests getting stuck somewhere in the device for no visible
> reason.  This event provides a means to inform the management layer of
> this situation in a timely fashion.
>
> The event could be reused for some other virtqueue problems (not only
> for vhost devices) in future. For this it gets a generic name and
> structure.
>
> We keep original VHOST_OPS_DEBUG(), to keep original debug output as is
> here, it's not the only call to VHOST_OPS_DEBUG in the file.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---

[...]

> diff --git a/qapi/qdev.json b/qapi/qdev.json
> index 6bc5a733b8..199e21cae7 100644
> --- a/qapi/qdev.json
> +++ b/qapi/qdev.json
> @@ -161,3 +161,28 @@
>  ##
>  { 'event': 'DEVICE_UNPLUG_GUEST_ERROR',
>    'data': { '*device': 'str', 'path': 'str' } }
> +
> +##
> +# @VirtqueueError:
> +#

Missing member documentation:

    # @vhost-vring-err: Lorem ipsum dolor sit amet, consectetur adipiscing
    #     elit, sed do eiusmod tempor incididunt ut labore et dolore magna
    #     aliqua.

> +# Since: 8.2
> +##
> +{ 'enum': 'VirtqueueError',
> +  'data': [ 'vhost-vring-err' ] }

Let's not abbreviate "error" to "err" here.

> +
> +##
> +# @VIRTQUEUE_ERROR:
> +#
> +# Emitted when a device virtqueue fails in runtime.
> +#
> +# @device: the device's ID if it has one
> +# @path: the device's QOM path
> +# @virtqueue: virtqueue index
> +# @error: error identifier
> +# @description: human readable description
> +#
> +# Since: 8.2
> +##
> +{ 'event': 'VIRTQUEUE_ERROR',
> + 'data': { '*device': 'str', 'path': 'str', 'virtqueue': 'int',
> +            'error': 'VirtqueueError', 'description': 'str'} }