[PATCH] virtio: add VIRTQUEUE_ERROR QAPI event

[Vladimir Sementsov-Ogievskiy]

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 coredums or do some other debugging

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.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@yandex-team.ru>
---
 hw/virtio/vhost.c | 12 +++++++++---
 qapi/qdev.json    | 25 +++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index f758f177bb..caa81f2ace 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -15,6 +15,7 @@
 
 #include "qemu/osdep.h"
 #include "qapi/error.h"
+#include "qapi/qapi-events-qdev.h"
 #include "hw/virtio/vhost.h"
 #include "qemu/atomic.h"
 #include "qemu/range.h"
@@ -1287,11 +1288,16 @@ static void 
vhost_virtqueue_error_notifier(EventNotifier *n)
     struct vhost_virtqueue *vq = container_of(n, struct vhost_virtqueue,
                                               error_notifier);
     struct vhost_dev *dev = vq->dev;
-    int index = vq - dev->vqs;
 
     if (event_notifier_test_and_clear(n) && dev->vdev) {
-        VHOST_OPS_DEBUG(-EINVAL,  "vhost vring error in virtqueue %d",
-                        dev->vq_index + index);
+        int ind = vq - dev->vqs + dev->vq_index;
+        DeviceState *ds = &dev->vdev->parent_obj;
+
+        VHOST_OPS_DEBUG(-EINVAL,  "vhost vring error in virtqueue %d", ind);
+        qapi_event_send_virtqueue_error(!!ds->id, ds->id, ds->canonical_path,
+                                        ind, VIRTQUEUE_ERROR_VHOST_VRING_ERR,
+                                        "vhost reported failure through vring "
+                                        "error fd");
     }
 }
 
diff --git a/qapi/qdev.json b/qapi/qdev.json
index 2708fb4e99..b7c2669c2c 100644
--- a/qapi/qdev.json
+++ b/qapi/qdev.json
@@ -158,3 +158,28 @@
 ##
 { 'event': 'DEVICE_UNPLUG_GUEST_ERROR',
   'data': { '*device': 'str', 'path': 'str' } }
+
+##
+# @VirtqueueError:
+#
+# Since: 7.2
+##
+{ 'enum': 'VirtqueueError',
+  'data': [ 'vhost-vring-err' ] }
+
+##
+# @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: 7.2
+##
+{ 'event': 'VIRTQUEUE_ERROR',
+ 'data': { '*device': 'str', 'path': 'str', 'virtqueue': 'int',
+            'error': 'VirtqueueError', 'description': 'str'} }
-- 
2.25.1