qapi: add qom-path to BLOCK_IO_ERROR event

We need something more reliable than "device" (which absent in modern
interfaces) and "node-name" (which may absent, and actually don't
specify the device, which is a source of error) to make a per-device
throttling for the event in the following commit.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-ID: <20241002151806.592469-2-vsementsov@yandex-team.ru>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/block-backend.c

@@ -1019,22 +1019,34 @@ DeviceState *blk_get_attached_dev(BlockBackend *blk)
     return blk->dev;
 }
 
-/* Return the qdev ID, or if no ID is assigned the QOM path, of the block
- * device attached to the BlockBackend. */
-char *blk_get_attached_dev_id(BlockBackend *blk)
+static char *blk_get_attached_dev_id_or_path(BlockBackend *blk, bool want_id)
 {
     DeviceState *dev = blk->dev;
     IO_CODE();
 
     if (!dev) {
         return g_strdup("");
-    } else if (dev->id) {
+    } else if (want_id && dev->id) {
         return g_strdup(dev->id);
     }
 
     return object_get_canonical_path(OBJECT(dev)) ?: g_strdup("");
 }
 
+/*
+ * Return the qdev ID, or if no ID is assigned the QOM path, of the block
+ * device attached to the BlockBackend.
+ */
+char *blk_get_attached_dev_id(BlockBackend *blk)
+{
+    return blk_get_attached_dev_id_or_path(blk, true);
+}
+
+static char *blk_get_attached_dev_path(BlockBackend *blk)
+{
+    return blk_get_attached_dev_id_or_path(blk, false);
+}
+
 /*
  * Return the BlockBackend which has the device model @dev attached if it
  * exists, else null.
@@ -2125,6 +2137,7 @@ static void send_qmp_error_event(BlockBackend *blk,
 
     optype = is_read ? IO_OPERATION_TYPE_READ : IO_OPERATION_TYPE_WRITE;
     qapi_event_send_block_io_error(blk_name(blk),
+                                   blk_get_attached_dev_path(blk),
                                    bs ? bdrv_get_node_name(bs) : NULL, optype,
                                    action, blk_iostatus_is_enabled(blk),
                                    error == ENOSPC, strerror(error));

qapi/block-core.json

@@ -5584,6 +5584,8 @@
 #
 # Emitted when a disk I/O error occurs
 #
+# @qom-path: path to the device object in the QOM tree (since 9.2)
+#
 # @device: device name.  This is always present for compatibility
 #     reasons, but it can be empty ("") if the image does not have a
 #     device name associated.
@@ -5614,7 +5616,8 @@
 # .. qmp-example::
 #
 #     <- { "event": "BLOCK_IO_ERROR",
-#          "data": { "device": "ide0-hd1",
+#          "data": { "qom-path": "/machine/unattached/device[0]",
+#                    "device": "ide0-hd1",
 #                    "node-name": "#block212",
 #                    "operation": "write",
 #                    "action": "stop",
@@ -5622,7 +5625,7 @@
 #          "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
 ##
 { 'event': 'BLOCK_IO_ERROR',
-  'data': { 'device': 'str', '*node-name': 'str',
+  'data': { 'qom-path': 'str', 'device': 'str', '*node-name': 'str',
             'operation': 'IoOperationType',
             'action': 'BlockErrorAction', '*nospace': 'bool',
             'reason': 'str' } }