[PATCH 4/4] vhost: forward vring errors into virtio device

[Konstantin Khlebnikov <khlebnikov@yandex-team.ru>]

Setup eventfd for vring error notifications.
Add eventfd for each virt-queue to detect which queue faced error.

For example vhost-net in kernel silently stop working at first error.
Now we'll see message and qmp event if guest driver did something wrong.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
 hw/virtio/vhost.c         |   37 +++++++++++++++++++++++++++++++++++++
 include/hw/virtio/vhost.h |    1 +
 2 files changed, 38 insertions(+)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index dd3263df56..5015e1fd81 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1274,6 +1274,19 @@ static int vhost_virtqueue_set_busyloop_timeout(struct vhost_dev *dev,
     return 0;
 }
 
+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) {
+        virtio_error(dev->vdev, "vhost vring error in virtqueue %d",
+                     dev->vq_index + index);
+    }
+}
+
 static int vhost_virtqueue_init(struct vhost_dev *dev,
                                 struct vhost_virtqueue *vq, int n)
 {
@@ -1295,7 +1308,27 @@ static int vhost_virtqueue_init(struct vhost_dev *dev,
 
     vq->dev = dev;
 
+    if (dev->vhost_ops->vhost_set_vring_err) {
+        r = event_notifier_init(&vq->error_notifier, 0);
+        if (r < 0) {
+            goto fail_call;
+        }
+
+        file.fd = event_notifier_get_fd(&vq->error_notifier);
+        r = dev->vhost_ops->vhost_set_vring_err(dev, &file);
+        if (r) {
+            VHOST_OPS_DEBUG(r, "vhost_set_vring_err failed");
+            goto fail_err;
+        }
+
+        event_notifier_set_handler(&vq->error_notifier,
+                                   vhost_virtqueue_error_notifier);
+    }
+
     return 0;
+
+fail_err:
+    event_notifier_cleanup(&vq->error_notifier);
 fail_call:
     event_notifier_cleanup(&vq->masked_notifier);
     return r;
@@ -1304,6 +1337,10 @@ fail_call:
 static void vhost_virtqueue_cleanup(struct vhost_virtqueue *vq)
 {
     event_notifier_cleanup(&vq->masked_notifier);
+    if (vq->dev->vhost_ops->vhost_set_vring_err) {
+        event_notifier_set_handler(&vq->error_notifier, NULL);
+        event_notifier_cleanup(&vq->error_notifier);
+    }
 }
 
 int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index b291fe4e24..1e7cbd9a10 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -29,6 +29,7 @@ struct vhost_virtqueue {
     unsigned long long used_phys;
     unsigned used_size;
     EventNotifier masked_notifier;
+    EventNotifier error_notifier;
     struct vhost_dev *dev;
 };