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Re: [Qemu-devel] [PATCH v3 0/9] block: generic image streaming

From: Yibin Shen
Subject: Re: [Qemu-devel] [PATCH v3 0/9] block: generic image streaming
Date: Wed, 14 Dec 2011 09:42:34 +0800

On Tue, Dec 13, 2011 at 11:18 PM, Stefan Hajnoczi <address@hidden> wrote:
> On Tue, Dec 13, 2011 at 2:12 PM, Yibin Shen <address@hidden> wrote:
>> all these patches looks good to me except one thing,
>> when I run a "qemu-img commit" command,
>> seems entire image(from start to end sector) will be write to the backing 
>> file,
>> I think what we really need is to commit only dirty sectors.
>> also maybe we can use a writeback mechanism alternaively.
> This series does not affect the behavior of "qemu-img commit".
> Are you suggesting a new feature?  Please explain a little more.
yes , I suggest a new feature,

in some situation, we need to commit data in qed image to backing file.
in old days ,people without copy-on-read, they only have copy-on-write,
so 'qemu-img commit' commit all exsits data to backing file is rational.

but with copy-on-read or image streaming,
which means most data in the image may be identical with backing file,
so commit entire image is a redundant operation.

can we record the dirty bitmap for data differ from backing file,
then in a commit operation, we only need to handle minimum data.

> Stefan


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