[Qemu-devel] [RFC for-2.7 1/1] block/qapi: Add query-block-node-tree

[Max Reitz <mreitz@redhat.com>]

This command returns the tree of BlockDriverStates under a given root
node.

Every tree node is described by its node name and the connection of a
parent node to its children additionally contains the role the child
assumes.

A node's name can then be used e.g. in conjunction with
query-named-block-nodes to get more information about the node.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qapi.c         | 43 +++++++++++++++++++++++++++++++++++++++++++
 qapi/block-core.json | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 qmp-commands.hx      | 38 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 127 insertions(+)

diff --git a/block/qapi.c b/block/qapi.c
index 6a4869a..a35d32b 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -493,6 +493,49 @@ BlockInfoList *qmp_query_block(Error **errp)
     return head;
 }
 
+static BlockNodeTreeNode *qmp_query_block_node_tree_by_bs(BlockDriverState *bs)
+{
+    BlockNodeTreeNode *bntn;
+    BlockNodeTreeChildList **p_next;
+    BdrvChild *child;
+
+    bntn = g_new0(BlockNodeTreeNode, 1);
+
+    bntn->node_name = g_strdup(bdrv_get_node_name(bs));
+    bntn->has_node_name = bntn->node_name;
+
+    p_next = &bntn->children;
+    QLIST_FOREACH(child, &bs->children, next) {
+        BlockNodeTreeChild *bntc;
+
+        bntc = g_new(BlockNodeTreeChild, 1);
+        *bntc = (BlockNodeTreeChild){
+            .role = g_strdup(child->name),
+            .node = qmp_query_block_node_tree_by_bs(child->bs),
+        };
+
+        *p_next = g_new0(BlockNodeTreeChildList, 1);
+        (*p_next)->value = bntc;
+        p_next = &(*p_next)->next;
+    }
+
+    *p_next = NULL;
+    return bntn;
+}
+
+BlockNodeTreeNode *qmp_query_block_node_tree(const char *root_node,
+                                             Error **errp)
+{
+    BlockDriverState *bs;
+
+    bs = bdrv_lookup_bs(root_node, root_node, errp);
+    if (!bs) {
+        return NULL;
+    }
+
+    return qmp_query_block_node_tree_by_bs(bs);
+}
+
 static bool next_query_bds(BlockBackend **blk, BlockDriverState **bs,
                            bool query_nodes)
 {
diff --git a/qapi/block-core.json b/qapi/block-core.json
index b1cf77d..754ccd6 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -470,6 +470,52 @@
 
 
 ##
+# @BlockNodeTreeNode:
+#
+# Describes a node in the block node graph.
+#
+# @node-name: If present, the node's name.
+#
+# @children:  List of the node's children.
+#
+# Since: 2.7
+##
+{ 'struct': 'BlockNodeTreeNode',
+  'data': { '*node-name': 'str',
+            'children': ['BlockNodeTreeChild'] } }
+
+##
+# @BlockNodeTreeChild:
+#
+# Describes a child node in the block node graph.
+#
+# @role: Role the child assumes for its parent, e.g. "file" or "backing".
+#
+# @node: The child node's BlockNodeTreeNode structure.
+#
+# Since: 2.7
+##
+{ 'struct': 'BlockNodeTreeChild',
+  'data': { 'role': 'str',
+            'node': 'BlockNodeTreeNode' } }
+
+##
+# @query-block-node-tree:
+#
+# Queries the tree of nodes under a given node in the block graph.
+#
+# @root-node: Node name or device name of the tree's root node.
+#
+# Returns: The root node's BlockNodeTreeNode structure.
+#
+# Since: 2.7
+##
+{ 'command': 'query-block-node-tree',
+  'data': { 'root-node': 'str' },
+  'returns': 'BlockNodeTreeNode' }
+
+
+##
 # @BlockDeviceTimedStats:
 #
 # Statistics of a block device during a given interval of time.
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 9e05365..5c404aa 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -2637,6 +2637,44 @@ EQMP
     },
 
 SQMP
+query-block-node-tree
+---------------------
+
+Queries the tree of nodes under a given node in the block graph.
+
+Arguments:
+
+- "root-node": Node name or device name of the tree's root node (json-string)
+
+The block node tree is represented with BlockNodeTreeNode and BlockNodeTreeChild
+json-objects.
+
+Each BlockNodeTreeNode json-object contains the following:
+
+- "node-name": If present, the node's name (json-string, optional)
+- "children": json-array of the node's children, each entry is a json-object of
+              type BlockNodeTreeChild
+
+Each BlockNodeTreeChild json-object contains the following:
+
+- "role": Role the child node assumes for its parent, e.g. "file" or "backing"
+          (json-string)
+- "node": BlockNodeTreeNode describing the child node (json-object)
+
+The cyclic reference of BlockNodeTreeNode and BlockNodeTreeChild to each other
+thus spawns a tree.
+
+This command returns the root node's BlockNodeTreeNode structure.
+
+EQMP
+
+    {
+        .name       = "query-block-node-tree",
+        .args_type  = "root-node:B",
+        .mhandler.cmd_new = qmp_marshal_query_block_node_tree,
+    },
+
+SQMP
 query-blockstats
 ----------------
 
-- 
2.7.4