[RFC v2 2/6] qmp: add QMP command virtio-status

[Laurent Vivier <lvivier@redhat.com>]

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

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---

Notes:
    v2: change field names to stick to naming conventions (s/_/-/)
        use an enum for the endianness

 hw/virtio/virtio-stub.c |  5 +++
 hw/virtio/virtio.c      | 50 +++++++++++++++++++++++++++
 qapi/virtio.json        | 76 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 131 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 4955fbe5a71b..539dc47e9952 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -3840,6 +3840,56 @@ 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 = VIRTIO_STATUS_ENDIANNESS_LITTLE;
+        break;
+    case VIRTIO_DEVICE_ENDIAN_BIG:
+        status->device_endian = VIRTIO_STATUS_ENDIANNESS_BIG;
+        break;
+    default:
+        status->device_endian = VIRTIO_STATUS_ENDIANNESS_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 fa3c7961ecff..504b235d7628 100644
--- a/qapi/virtio.json
+++ b/qapi/virtio.json
@@ -66,3 +66,79 @@
 ##
 
 { 'command': 'query-virtio', 'returns': ['VirtioInfo'] }
+
+##
+# @VirtioStatusEndianness:
+#
+# Enumeration of endianness for VirtioDevice
+#
+# Since: 5.1
+##
+{ 'enum': 'VirtioStatusEndianness',
+  'data': [ 'unknown', 'little', 'big' ]
+}
+
+##
+# @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': 'VirtioStatusEndianness',
+    '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'
+}
-- 
2.25.2