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From: Wen Congyang <wency@cn.fujitsu.com>
Message-ID: <55C403CB.801@cn.fujitsu.com>
Date: Fri, 7 Aug 2015 09:03:07 +0800
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Subject: Re: [Qemu-devel] [PATCH for-2.5 3/6] Add new block driver interface
 to add/delete a BDS's child
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To: Alberto Garcia <berto@igalia.com>, qemu devel <qemu-devel@nongnu.org>, Eric Blake <eblake@redhat.com>, Markus Armbruster <armbru@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, zhanghailiang <zhang.zhanghailiang@huawei.com>, qemu block <qemu-block@nongnu.org>, Jiang Yunhong <yunhong.jiang@intel.com>, Dong Eddie <eddie.dong@intel.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Gonglei <arei.gonglei@huawei.com>, Yang Hongyang <yanghy@cn.fujitsu.com>

On 08/06/2015 10:33 PM, Alberto Garcia wrote:
> On Fri 31 Jul 2015 11:19:12 AM CEST, Wen Congyang wrote:
> 
>> +/*
>> + * 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_id_or_node_name(bs));
>> +        return;
>> +    }
>> +
>> +    bs->drv->bdrv_add_child(bs, options, errp);
>> +}
>> +
>> +void bdrv_del_child(BlockDriverState *bs, BlockDriverState *child_bs,
>> +                    Error **errp)
>> +{
>> +    BdrvChild *child;
>> +
>> +    if (!bs->drv || !bs->drv->bdrv_del_child) {
>> +        error_setg(errp, "The BDS %s doesn't support removing a child",
>> +                   bdrv_get_id_or_node_name(bs));
>> +        return;
>> +    }
>> +
>> +    QLIST_FOREACH(child, &bs->children, next) {
>> +        if (child->bs == child_bs) {
>> +            break;
>> +        }
>> +    }
>> +
>> +    if (!child) {
>> +        error_setg(errp, "The BDS %s is not the BDS %s's child",
>> +                   bdrv_get_id_or_node_name(child_bs),
>> +                   bdrv_get_id_or_node_name(bs));
>> +        return;
>> +    }
>> +
>> +    bs->drv->bdrv_del_child(bs, child_bs, errp);
>> +}
> 
> I see that bdrv_del_child() checks that the child is in bs->children,
> but who takes care of putting it there in the first place?

The child is opened by the function bdrv_open_image().
bdrv_open_image()
    bdrv_open_child()
        bdrv_attach_child()

Thanks
Wen Congyang

> 
> Berto
> .
>