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Date: Thu, 18 Jun 2015 22:36:39 +0800
From: Wen Congyang <ghostwcy@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: Stefan Hajnoczi <stefanha@gmail.com>, 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>

At 2015/6/18 20:55, Stefan Hajnoczi Wrote:
> 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.

Where should it be documented? In the header file?

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

The purpos is that: don't connect to nbd server when opening a nbd 
client. connect/disconnect
to nbd server when we need to do it.

IIUC, if bs->drv is NULL, it means that the driver is ejected? Here, 
connect/disconnect
means that connect/disconnect to remote target(The target may be in 
another host).

Thanks
Wen Congyang