block/qapi: Introduce BlockGraphInfo

Introduce a new QAPI type BlockGraphInfo and an associated
bdrv_query_block_graph_info() function that recursively gathers
BlockNodeInfo objects through a block graph.

A follow-up patch is going to make "qemu-img info" use this to print
information about all nodes that are (usually implicitly) opened for a
given image file.

Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220620162704.80987-8-hreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/qapi.c

@@ -403,6 +403,54 @@ fail:
     qapi_free_ImageInfo(info);
 }
 
+/**
+ * bdrv_query_block_graph_info:
+ * @bs: root node to start from
+ * @p_info: location to store image information
+ * @errp: location to store error information
+ *
+ * Store image information about the graph starting from @bs in @p_info.
+ *
+ * @p_info will be set only on success. On error, store error in @errp.
+ */
+void bdrv_query_block_graph_info(BlockDriverState *bs,
+                                 BlockGraphInfo **p_info,
+                                 Error **errp)
+{
+    BlockGraphInfo *info;
+    BlockChildInfoList **children_list_tail;
+    BdrvChild *c;
+    ERRP_GUARD();
+
+    info = g_new0(BlockGraphInfo, 1);
+    bdrv_do_query_node_info(bs, qapi_BlockGraphInfo_base(info), errp);
+    if (*errp) {
+        goto fail;
+    }
+
+    children_list_tail = &info->children;
+
+    QLIST_FOREACH(c, &bs->children, next) {
+        BlockChildInfo *c_info;
+
+        c_info = g_new0(BlockChildInfo, 1);
+        QAPI_LIST_APPEND(children_list_tail, c_info);
+
+        c_info->name = g_strdup(c->name);
+        bdrv_query_block_graph_info(c->bs, &c_info->info, errp);
+        if (*errp) {
+            goto fail;
+        }
+    }
+
+    *p_info = info;
+    return;
+
+fail:
+    assert(*errp != NULL);
+    qapi_free_BlockGraphInfo(info);
+}
+
 /* @p_info will be set only on success. */
 static void bdrv_query_info(BlockBackend *blk, BlockInfo **p_info,
                             Error **errp)

include/block/qapi.h

@@ -43,6 +43,9 @@ void bdrv_query_image_info(BlockDriverState *bs,
                            bool flat,
                            bool skip_implicit_filters,
                            Error **errp);
+void bdrv_query_block_graph_info(BlockDriverState *bs,
+                                 BlockGraphInfo **p_info,
+                                 Error **errp);
 
 void bdrv_snapshot_dump(QEMUSnapshotInfo *sn);
 void bdrv_image_info_specific_dump(ImageInfoSpecific *info_spec,

qapi/block-core.json

@@ -307,6 +307,41 @@
       '*backing-image': 'ImageInfo'
   } }
 
+##
+# @BlockChildInfo:
+#
+# Information about all nodes in the block graph starting at some node,
+# annotated with information about that node in relation to its parent.
+#
+# @name: Child name of the root node in the BlockGraphInfo struct, in its role
+#        as the child of some undescribed parent node
+#
+# @info: Block graph information starting at this node
+#
+# Since: 8.0
+##
+{ 'struct': 'BlockChildInfo',
+  'data': {
+      'name': 'str',
+      'info': 'BlockGraphInfo'
+  } }
+
+##
+# @BlockGraphInfo:
+#
+# Information about all nodes in a block (sub)graph in the form of BlockNodeInfo
+# data.
+# The base BlockNodeInfo struct contains the information for the (sub)graph's
+# root node.
+#
+# @children: Array of links to this node's child nodes' information
+#
+# Since: 8.0
+##
+{ 'struct': 'BlockGraphInfo',
+  'base': 'BlockNodeInfo',
+  'data': { 'children': ['BlockChildInfo'] } }
+
 ##
 # @ImageCheck:
 #