Re: [Qemu-devel] [PATCH v10 3/3] qmp: add monitor command to add/remove a child

[Max Reitz]

On 16.02.2016 10:37, Changlong Xie wrote:
> 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 | 32 +++++++++++++++++++++++++++++++
>  qmp-commands.hx      | 50 ++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 136 insertions(+)
> 
> diff --git a/blockdev.c b/blockdev.c
> index 1f73478..ca040b0 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -3983,6 +3983,60 @@ 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;
> +}

As I said for patch 1, making this function return a BdrvChild would be
trivial...

> +
> +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 parameters child and node are in 
> conflict");
> +        } else {
> +            error_setg(errp, "Either child or node must be specified");
> +        }
> +        return;
> +    }
> +
> +    if (has_child) {
> +        child_bs = bdrv_find_child(parent_bs, child);
> +        if (!child_bs) {
> +            error_setg(errp, "Node '%s' does not have child '%s'",
> +                       parent, child);
> +            return;
> +        }
> +        bdrv_del_child(parent_bs, child_bs, errp);

...and then we could pass the BdrvChild here.

(It's your choice.)

> +    }
> +
> +    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 33012b8..92eb7fe 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -2482,3 +2482,35 @@
>  ##
>  { '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 020e5ee..1c9a06f 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -4364,6 +4364,56 @@ 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.

The explanation of its behavior is missing here (the second paragraph in
the qapi/block-core.json comment).

Max

> +
> +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",
> +                                "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,
>

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