qmp: add monitor command to add/remove a child

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 <wency@cn.fujitsu.com>
Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: Gonglei <arei.gonglei@huawei.com>
Signed-off-by: Changlong Xie <xiecl.fnst@cn.fujitsu.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 1462865799-19402-4-git-send-email-xiecl.fnst@cn.fujitsu.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

blockdev.c

@@ -4092,6 +4092,61 @@ out:
     aio_context_release(aio_context);
 }
 
+static BdrvChild *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;
+        }
+    }
+
+    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, *new_bs = NULL;
+    BdrvChild *p_child;
+
+    parent_bs = bdrv_lookup_bs(parent, parent, errp);
+    if (!parent_bs) {
+        return;
+    }
+
+    if (has_child == has_node) {
+        if (has_child) {
+            error_setg(errp, "The parameters child and node are in conflict");
+        } else {
+            error_setg(errp, "Either child or node must be specified");
+        }
+        return;
+    }
+
+    if (has_child) {
+        p_child = bdrv_find_child(parent_bs, child);
+        if (!p_child) {
+            error_setg(errp, "Node '%s' does not have child '%s'",
+                       parent, child);
+            return;
+        }
+        bdrv_del_child(parent_bs, p_child, 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;

qapi/block-core.json

@@ -2556,3 +2556,35 @@
 ##
 { '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 graph node. Currently only the
+# Quorum driver implements this feature to add or remove its child. This
+# is useful to fix a broken quorum child.
+#
+# If @node is specified, it will be inserted under @parent. @child
+# may not be specified in this case. If both @parent and @child are
+# specified but @node is not, @child will be detached from @parent.
+#
+# @parent: the id or name of the parent node.
+#
+# @child: #optional the name of a child under the given parent node.
+#
+# @node: #optional the name of the node that will be added.
+#
+# Note: this command is experimental, and its API is not stable. It
+# does not support all kinds of operations, all kinds of children, nor
+# all block drivers.
+#
+# Warning: The data in a new quorum child MUST be consistent with that of
+# the rest of the array.
+#
+# Since: 2.7
+##
+{ 'command': 'x-blockdev-change',
+  'data' : { 'parent': 'str',
+             '*child': 'str',
+             '*node': 'str' } }

qmp-commands.hx

@@ -4395,6 +4395,59 @@ Example:
 
 <- { "return": {} }
 
+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 graph node. Currently only the
+Quorum driver implements this feature to add or remove its child. This
+is useful to fix a broken quorum child.
+
+If @node is specified, it will be inserted under @parent. @child
+may not be specified in this case. If both @parent and @child are
+specified but @node is not, @child will be detached from @parent.
+
+Arguments:
+- "parent": the id or name of the parent node (json-string)
+- "child": the name of a child under the given parent node (json-string, optional)
+- "node": the name of the node that 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.
+
+Warning: The data in a new quorum child MUST be consistent with that of
+the rest of the array.
+
+Example:
+
+Add a new node to a quorum
+-> { "execute": "blockdev-add",
+     "arguments": { "options": { "driver": "raw",
+                                 "node-name": "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
 
     {