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Date: Wed, 27 Nov 2013 14:40:05 +0800
From: Fam Zheng <famz@redhat.com>
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Subject: Re: [Qemu-devel] [RFC PATCH v2 5/6] qcow2: implement
	bdrv_preallocate
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To: Hu Tao <hutao@cn.fujitsu.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Peter Lieven <pl@kamp.de>, qemu-devel@nongnu.org

On 2013=E5=B9=B411=E6=9C=8827=E6=97=A5 14:01, Hu Tao wrote:
> On Wed, Nov 27, 2013 at 11:01:23AM +0800, Fam Zheng wrote:
>> On 2013=E5=B9=B411=E6=9C=8827=E6=97=A5 10:15, Hu Tao wrote:
>>> Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
>>> ---
>>>   block/qcow2.c | 7 +++++++
>>>   1 file changed, 7 insertions(+)
>>>
>>> diff --git a/block/qcow2.c b/block/qcow2.c
>>> index b054a01..a23fade 100644
>>> --- a/block/qcow2.c
>>> +++ b/block/qcow2.c
>>> @@ -2180,6 +2180,12 @@ static int qcow2_amend_options(BlockDriverStat=
e *bs,
>>>       return 0;
>>>   }
>>>
>>> +static int qcow2_preallocate(BlockDriverState *bs, int64_t offset,
>>> +                             int64_t length)
>>> +{
>>> +    return bdrv_preallocate(bs->file, offset, length);
>>> +}
>>> +
>>
>> What's the semantics of .bdrv_preallocate? I think you should map
>> [offset, offset + length) to clusters in image file, and then
>> forward to bs->file, rather than this direct wrapper.
>>
>> E.g. bdrv_preallocate(qcow2_bs, 0, cluster_size) should call
>> bdrv_preallocate(qcow2_bs->file, offset_off_first_cluster,
>> cluster_size).
>
> You mean data clusters here, right? Is there a single function to get
> the offset of the first data cluster?
>

There is a function, qcow2_get_cluster_offset.

Fam