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Date: Thu, 18 Jun 2015 13:55:33 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] [Qemu-block] [PATCH COLO-Block v6 07/16] Add new
 block driver interface to connect/disconnect the remote target
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To: Wen Congyang <wency@cn.fujitsu.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, qemu block <qemu-block@nongnu.org>, Jiang Yunhong <yunhong.jiang@intel.com>, Dong Eddie <eddie.dong@intel.com>, qemu devel <qemu-devel@nongnu.org>, Max Reitz <mreitz@redhat.com>, Gonglei <arei.gonglei@huawei.com>, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Yang Hongyang <yanghy@cn.fujitsu.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, zhanghailiang <zhang.zhanghailiang@huawei.com>


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On Thu, Jun 18, 2015 at 04:49:12PM +0800, Wen Congyang wrote:
> +void bdrv_connect(BlockDriverState *bs, Error **errp)
> +{
> +    BlockDriver *drv = bs->drv;
> +
> +    if (drv && drv->bdrv_connect) {
> +        drv->bdrv_connect(bs, errp);
> +    } else if (bs->file) {
> +        bdrv_connect(bs->file, errp);
> +    } else {
> +        error_setg(errp, "this feature or command is not currently supported");
> +    }
> +}
> +
> +void bdrv_disconnect(BlockDriverState *bs)
> +{
> +    BlockDriver *drv = bs->drv;
> +
> +    if (drv && drv->bdrv_disconnect) {
> +        drv->bdrv_disconnect(bs);
> +    } else if (bs->file) {
> +        bdrv_disconnect(bs->file);
> +    }
> +}

Please add doc comments describing the semantics of these commands.

Why are these operations needed when there is already a bs->drv == NULL
case which means the BDS is not ready for read/write?

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