[Qemu-devel] [PATCH v2 2/8] virtio: enhance virtio_error messages

[Ladi Prosek <lprosek@redhat.com>]

Output like "Virtqueue size exceeded" is not much useful in identifying the
culprit. This commit adds virtio device name (e.g. "virtio-input") and id
if set (e.g. "mouse0") to all virtio error messages to improve debuggability.

Some virtio devices (virtio-scsi, virtio-serial) insert a bus between the
proxy object and the virtio backends, so a helper function is added to walk
the object hierarchy and find the right proxy object to extract the id from.

Signed-off-by: Ladi Prosek <lprosek@redhat.com>
---
 hw/virtio/virtio.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 0e76a73..a98f681 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -31,6 +31,11 @@
  */
 #define VIRTIO_PCI_VRING_ALIGN         4096
 
+/*
+ * Name of the property linking proxy objects to virtio backend objects.
+ */
+#define VIRTIO_PROP_BACKEND            "virtio-backend"
+
 typedef struct VRingDesc
 {
     uint64_t addr;
@@ -2223,7 +2228,8 @@ void virtio_instance_init_common(Object *proxy_obj, void *data,
     DeviceState *vdev = data;
 
     object_initialize(vdev, vdev_size, vdev_name);
-    object_property_add_child(proxy_obj, "virtio-backend", OBJECT(vdev), NULL);
+    object_property_add_child(proxy_obj, VIRTIO_PROP_BACKEND, OBJECT(vdev),
+                              NULL);
     object_unref(OBJECT(vdev));
     qdev_alias_all_properties(vdev, proxy_obj);
 }
@@ -2443,12 +2449,29 @@ void virtio_device_set_child_bus_name(VirtIODevice *vdev, char *bus_name)
     vdev->bus_name = g_strdup(bus_name);
 }
 
+static const char *virtio_get_device_id(VirtIODevice *vdev)
+{
+    DeviceState *qdev = DEVICE(vdev);
+    while (qdev) {
+        /* Find the proxy object corresponding to the vdev backend */
+        Object *prop = object_property_get_link(OBJECT(qdev),
+                                                VIRTIO_PROP_BACKEND, NULL);
+        if (prop == OBJECT(vdev)) {
+            return qdev->id;
+        }
+        qdev = qdev->parent_bus->parent;
+    }
+    return NULL;
+}
+
 void GCC_FMT_ATTR(2, 3) virtio_error(VirtIODevice *vdev, const char *fmt, ...)
 {
     va_list ap;
 
+    error_report_nolf("%s (id=%s): ", vdev->name, virtio_get_device_id(vdev));
+
     va_start(ap, fmt);
-    error_vreport_nolf(fmt, ap);
+    error_vprintf(fmt, ap);
     va_end(ap);
     error_printf("\n");
 
-- 
2.9.3