This new command shows the status of a VirtIODevice
(features, endianness and number of virtqueues)

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 hw/virtio/virtio-stub.c |  5 ++++
 hw/virtio/virtio.c      | 51 ++++++++++++++++++++++++++++++++
 qapi/virtio.json        | 65 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 121 insertions(+)

diff --git a/hw/virtio/virtio-stub.c b/hw/virtio/virtio-stub.c
index d9e4a815ecf1..8fe2d6cd8892 100644
--- a/hw/virtio/virtio-stub.c
+++ b/hw/virtio/virtio-stub.c
@@ -12,3 +12,8 @@ VirtioInfoList *qmp_query_virtio(Error **errp)
 {
     return qmp_virtio_unsupported(errp);
 }
+
+VirtioStatus *qmp_virtio_status(const char* path, Error **errp)
+{
+    return qmp_virtio_unsupported(errp);
+}
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 3cebc3d169c8..7f6e21e4ab2c 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -3839,6 +3839,57 @@ VirtioInfoList *qmp_query_virtio(Error **errp)
     return list;
 }
 
+static VirtIODevice *virtio_device_find(const char *path)
+{
+    VirtIODevice *vdev;
+
+    QTAILQ_FOREACH(vdev, &virtio_list, next) {
+        DeviceState *dev = DEVICE(vdev);
+
+        if (strcmp(dev->canonical_path, path) != 0) {
+            continue;
+        }
+        return vdev;
+    }
+
+    return NULL;
+}
+
+VirtioStatus *qmp_virtio_status(const char* path, Error **errp)
+{
+    VirtIODevice *vdev;
+    VirtioStatus *status;
+
+    vdev = virtio_device_find(path);
+    if (vdev == NULL) {
+        error_setg(errp, "Path %s is not a VirtIO device", path);
+        return NULL;
+    }
+
+    status = g_new0(VirtioStatus, 1);
+    status->guest_features = vdev->guest_features;
+    status->host_features = vdev->host_features;
+    status->backend_features = vdev->backend_features;
+    status->device_id = vdev->device_id;
+
+    switch (vdev->device_endian) {
+    case VIRTIO_DEVICE_ENDIAN_LITTLE:
+        status->device_endian = g_strdup("little");
+        break;
+    case VIRTIO_DEVICE_ENDIAN_BIG:
+        status->device_endian = g_strdup("big");
+        break;
+    case VIRTIO_DEVICE_ENDIAN_UNKNOWN:
+    default:
+        status->device_endian = g_strdup("unknown");
+        break;
+    }
+
+    status->num_vqs = virtio_get_num_queues(vdev);
+
+    return status;
+}
+
 static const TypeInfo virtio_device_info = {
     .name = TYPE_VIRTIO_DEVICE,
     .parent = TYPE_DEVICE,
diff --git a/qapi/virtio.json b/qapi/virtio.json
index 2a95d08a8b9e..2af4d95b9893 100644
--- a/qapi/virtio.json
+++ b/qapi/virtio.json
@@ -52,3 +52,68 @@
 ##
 
 { 'command': 'query-virtio', 'returns': ['VirtioInfo'] }
+
+##
+# @VirtioStatus:
+#
+# @device_id: VirtIODevice status
+#
+# @device_endian: VirtIODevice device_endian
+#
+# @guest_features: VirtIODevice guest_features
+#
+# @host_features: VirtIODevice host_features
+#
+# @backend_features: VirtIODevice backend_features
+#
+# @num_vqs: number of VirtIODevice queues
+#
+# Since: 5.1
+#
+##
+
+{ 'struct': 'VirtioStatus',
+  'data': {
+    'device_id': 'int',
+    'device_endian': 'str',
+    'guest_features': 'uint64',
+    'host_features': 'uint64',
+    'backend_features': 'uint64',
+    'num_vqs': 'uint16'
+  }
+}
+
+##
+# @virtio-status:
+#
+# Return the status of virtio device
+#
+# @path: QOBject path of the VirtIODevice
+#
+# Returns: status of the VirtIODevice
+#
+# Since: 5.1
+#
+# Example:
+#
+# -> { "execute": "virtio-status",
+#      "arguments": {
+#          "path": "/machine/peripheral-anon/device[3]/virtio-backend"
+#      }
+#   }
+# <- { "return": {
+#          "backend_features": 0,
+#          "guest_features": 5111807911,
+#          "num_vqs": 3,
+#          "host_features": 6337593319,
+#          "device_endian": "little",
+#          "device_id": 1
+#      }
+#    }
+#
+##
+
+{ 'command': 'virtio-status',
+  'data': { 'path': 'str' },
+  'returns': 'VirtioStatus'
+}
-- 
2.25.1

On 4/2/20 5:02 AM, Laurent Vivier wrote:
> This new command shows the status of a VirtIODevice
> (features, endianness and number of virtqueues)
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---

> +++ b/qapi/virtio.json
> @@ -52,3 +52,68 @@
>   ##
>   
>   { 'command': 'query-virtio', 'returns': ['VirtioInfo'] }
> +
> +##
> +# @VirtioStatus:
> +#
> +# @device_id: VirtIODevice status

As this is a new API, it should stick to our naming conventions:

device-id

> +#
> +# @device_endian: VirtIODevice device_endian

device-endian

> +#
> +# @guest_features: VirtIODevice guest_features

guest-features

> +#
> +# @host_features: VirtIODevice host_features

host-features

> +#
> +# @backend_features: VirtIODevice backend_features

backend-features

> +#
> +# @num_vqs: number of VirtIODevice queues

num-vqs

> +#
> +# Since: 5.1
> +#
> +##
> +
> +{ 'struct': 'VirtioStatus',
> +  'data': {
> +    'device_id': 'int',
> +    'device_endian': 'str',
> +    'guest_features': 'uint64',
> +    'host_features': 'uint64',
> +    'backend_features': 'uint64',

A bare int requires subsequent decoding.  Can this instead be an array 
of enum values, with enum values naming each enabled feature?

> +    'num_vqs': 'uint16'
> +  }
> +}
> +
> +##
> +# @virtio-status:
> +#
> +# Return the status of virtio device
> +#
> +# @path: QOBject path of the VirtIODevice
> +#
> +# Returns: status of the VirtIODevice
> +#
> +# Since: 5.1
> +#
> +# Example:
> +#
> +# -> { "execute": "virtio-status",
> +#      "arguments": {
> +#          "path": "/machine/peripheral-anon/device[3]/virtio-backend"
> +#      }
> +#   }
> +# <- { "return": {
> +#          "backend_features": 0,
> +#          "guest_features": 5111807911,

again, this means nothing to me.
   "guest-features": ["feature-a","feature-b"]
is vastly more usable if I'm inspecting the query output, compared to 
decoding the decimal number back into bits then doing a lookup into the 
documentation of which bits mean which features.

> +#          "num_vqs": 3,
> +#          "host_features": 6337593319,
> +#          "device_endian": "little",
> +#          "device_id": 1
> +#      }
> +#    }
> +#
> +##
> +
> +{ 'command': 'virtio-status',
> +  'data': { 'path': 'str' },
> +  'returns': 'VirtioStatus'
> +}
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org