Re: [Qemu-devel] [Patch for-2.5 v2 3/6] Add new block driver interface to add/delete a BDS's child

[Eric Blake <eblake@redhat.com>]

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On 08/11/2015 01:51 AM, Wen Congyang wrote:
> In some cases, we want to take a quorum child offline, and take
> another child online.
> 
> 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>
> Reviewed-by: Alberto Garcia <berto@igalia.com>
> ---
>  block.c                   | 43 +++++++++++++++++++++++++++++++++++++++++++
>  include/block/block.h     |  4 ++++
>  include/block/block_int.h |  5 +++++
>  3 files changed, 52 insertions(+)
> 

> + * Hot add/remove a BDS's child. So the user can take a child offline when
> + * it is broken and take a new child online
> + */
> +void bdrv_add_child(BlockDriverState *bs, QDict *options, Error **errp)
> +{
> +
> +    if (!bs->drv || !bs->drv->bdrv_add_child) {
> +        error_setg(errp, "The BDS %s doesn't support adding a child",
> +                   bdrv_get_device_or_node_name(bs));
> +        return;
> +    }
> +
> +    bs->drv->bdrv_add_child(bs, options, errp);

Should this also check that bs is not already a child of something?  Or
a bit looser, we may want to allow a BDS to be a child of multiple trees
(a common shared backing file), but we still definitely don't want to
allow nonsensical loops such as trying to make a BDS be hot-added as its
own child.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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