Re: [Qemu-devel] [PATCH v12 3/3] qmp: add monitor command to add/remove a child

[Changlong Xie <xiecl.fnst@cn.fujitsu.com>]

On 03/10/2016 10:49 AM, Changlong Xie wrote:
> From: Wen Congyang <wency@cn.fujitsu.com>
>
> 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>
> ---
>   blockdev.c           | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>   qapi/block-core.json | 32 ++++++++++++++++++++++++++++++
>   qmp-commands.hx      | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 141 insertions(+)
>
> diff --git a/blockdev.c b/blockdev.c
> index 0f20c65..435631e 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -4017,6 +4017,61 @@ 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;
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 9bf1b22..bc3fd0b 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -2548,3 +2548,35 @@
>   ##
>   { '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: 2.6
> +##
> +{ 'command': 'x-blockdev-change',
> +  'data' : { 'parent': 'str',
> +             '*child': 'str',
> +             '*node': 'str' } }
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index b629673..2a55135 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -4398,6 +4398,60 @@ 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 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",
> +                                "id": "test_new_node",

Since f21d96d04 block: Use BdrvChild in BlockBackend, if we want to 
create a node without BB, we should not pass " "id": "test_new_node" ",
will fix in next version.

Thanks
	-Xie
> +                                "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,
>