[Qemu-devel] [PATCH v9 3/3] qmp: add monitor command to add/remove a child

[Changlong Xie]

From: Wen Congyang <address@hidden>

The new QMP command name is x-blockdev-change. It's just for adding/removing
quorum's child now, and doesn't support all kinds of children, all kinds of
operations, nor all block drivers. So it is experimental now.

Signed-off-by: Wen Congyang <address@hidden>
Signed-off-by: zhanghailiang <address@hidden>
Signed-off-by: Gonglei <address@hidden>
Signed-off-by: Changlong Xie <address@hidden>
---
 blockdev.c           | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 qapi/block-core.json | 23 ++++++++++++++++++++++
 qmp-commands.hx      | 47 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 124 insertions(+)

diff --git a/blockdev.c b/blockdev.c
index 64dbfeb..4e62fdf 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3836,6 +3836,60 @@ out:
     aio_context_release(aio_context);
 }
 
+static BlockDriverState *bdrv_find_child(BlockDriverState *parent_bs,
+                                         const char *child_name)
+{
+    BdrvChild *child;
+
+    QLIST_FOREACH(child, &parent_bs->children, next) {
+        if (strcmp(child->name, child_name) == 0) {
+            return child->bs;
+        }
+    }
+
+    return NULL;
+}
+
+void qmp_x_blockdev_change(const char *parent, bool has_child,
+                           const char *child, bool has_node,
+                           const char *node, Error **errp)
+{
+    BlockDriverState *parent_bs, *child_bs = NULL, *new_bs = NULL;
+
+    parent_bs = bdrv_lookup_bs(parent, parent, errp);
+    if (!parent_bs) {
+        return;
+    }
+
+    if (has_child == has_node) {
+        if (has_child) {
+            error_setg(errp, "The paramter child and node is conflict");
+        } else {
+            error_setg(errp, "Either child or node should be specified");
+        }
+        return;
+    }
+
+    if (has_child) {
+        child_bs = bdrv_find_child(parent_bs, child);
+        if (!child_bs) {
+            error_setg(errp, "Node '%s' doesn't have child %s",
+                       parent, child);
+            return;
+        }
+        bdrv_del_child(parent_bs, child_bs, errp);
+    }
+
+    if (has_node) {
+        new_bs = bdrv_find_node(node);
+        if (!new_bs) {
+            error_setg(errp, "Node '%s' not found", node);
+            return;
+        }
+        bdrv_add_child(parent_bs, new_bs, errp);
+    }
+}
+
 BlockJobInfoList *qmp_query_block_jobs(Error **errp)
 {
     BlockJobInfoList *head = NULL, **p_next = &head;
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 1a5d9ce..fe63c6d 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -2408,3 +2408,26 @@
 ##
 { 'command': 'block-set-write-threshold',
   'data': { 'node-name': 'str', 'write-threshold': 'uint64' } }
+
+##
+# @x-blockdev-change
+#
+# Dynamically reconfigure the block driver state graph. It can be used
+# to add, remove, insert or replace a block driver state. Currently only
+# the Quorum driver implements this feature to add or remove its child.
+# This is useful to fix a broken quorum child.
+#
+# @parent: the id or name of the node that will be changed.
+#
+# @child: #optional the name of the child that will be deleted.
+#
+# @node: #optional the name of the node will be added.
+#
+# Note: this command is experimental, and its API is not stable.
+#
+# Since: 2.6
+##
+{ 'command': 'x-blockdev-change',
+  'data' : { 'parent': 'str',
+             '*child': 'str',
+             '*node': 'str' } }
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 7b235ee..efee0ca 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -4293,6 +4293,53 @@ Example:
 EQMP
 
     {
+        .name       = "x-blockdev-change",
+        .args_type  = "parent:B,child:B?,node:B?",
+        .mhandler.cmd_new = qmp_marshal_x_blockdev_change,
+    },
+
+SQMP
+x-blockdev-change
+-----------------
+
+Dynamically reconfigure the block driver state graph. It can be used to
+add, remove, insert, or replace a block driver state. Currently only
+the Quorum driver implements this feature to add and remove its child.
+This is useful to fix a broken quorum child.
+
+Arguments:
+- "parent": the id or node name of which node will be changed (json-string)
+- "child": the child name which will be deleted (json-string, optional)
+- "node": the new node-name which will be added (json-string, optional)
+
+Note: this command is experimental, and not a stable API. It doesn't
+support all kinds of operations, all kinds of children, nor all block
+drivers.
+
+Example:
+
+Add a new node to a quorum
+-> { "execute": "blockdev-add",
+    "arguments": { "options": { "driver": "raw",
+                                "node-name": "new_node",
+                                "id": "test_new_node",
+                                "file": { "driver": "file",
+                                          "filename": "test.raw" } } } }
+<- { "return": {} }
+-> { "execute": "x-blockdev-change",
+    "arguments": { "parent": "disk1",
+                   "node": "new_node" } }
+<- { "return": {} }
+
+Delete a quorum's node
+-> { "execute": "x-blockdev-change",
+    "arguments": { "parent": "disk1",
+                   "child": "children.1" } }
+<- { "return": {} }
+
+EQMP
+
+    {
         .name       = "query-named-block-nodes",
         .args_type  = "",
         .mhandler.cmd_new = qmp_marshal_query_named_block_nodes,
-- 
1.9.3