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Date: Thu, 28 Apr 2011 08:36:26 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] Qemu-img convert with -B
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To: Brad Campbell <brad@fnarfbargle.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org, Brad Campbell <lists2009@fnarfbargle.com>

Am 28.04.2011 04:06, schrieb Brad Campbell:
> On 27/04/11 22:02, Brad Campbell wrote:
>> On 27/04/11 21:56, Kevin Wolf wrote:
>>
>>> When you don't have a backing file, leaving an cluster unallocated means
>>> that it's zero. When you have a backing file, it could be anything. So
>>> if qemu-img convert wanted to save this space, it would have to read
>>> from the backing file and leave the cluster unallocated if it reads as
>>> zero.
>>>
>>> This is something that qemu-img doesn't do today.
>>
> 
> This passes cursory testing, but I'm just wondering if this is along the 
> right lines?

I haven't checked all details, but it looks like what I would have done.
(Though something is wrong with your indentations, I suspect that the
patch wouldn't apply)

> @@ -939,9 +957,16 @@ out:
>       free_option_parameters(create_options);
>       free_option_parameters(param);
>       qemu_free(buf);
> +    if (buf3) {
> +        qemu_free(buf3);
> +    }

qemu_free (and the libc free, too) work just fine with NULL, so the
check isn't needed.

Kevin