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Re: [Qemu-devel] [PATCH 4/6] qemu-img: add-cow will not support convert

From: Dong Xu Wang
Subject: Re: [Qemu-devel] [PATCH 4/6] qemu-img: add-cow will not support convert
Date: Thu, 14 Jun 2012 22:17:35 +0800

On Thu, Jun 14, 2012 at 10:11 PM, Kevin Wolf <address@hidden> wrote:
> Am 14.06.2012 16:06, schrieb Dong Xu Wang:
>> On Thu, Jun 14, 2012 at 6:51 PM, Kevin Wolf <address@hidden> wrote:
>>> Am 13.06.2012 16:36, schrieb Dong Xu Wang:
>>>> add-cow file can't live alone, must together will image_file and 
>>>> backing_file.
>>>> If we implement qemu-img convert operation for add-cow file format, we must
>>>> create image_file and backing_file manually, that will be confused for 
>>>> users,
>>>> so we just ignore add-cow format while doing converting.
>>>> Signed-off-by: Dong Xu Wang <address@hidden>
>>> NACK.
>>> This stupid "let's drop the feature, it might confuse users" attitude is
>>> known from Gnome, but not from qemu.
>>> There's no technical reason to forbid it and anyone who manages to
>>> create a valid add-cow image will also be able to specify the very same
>>> options to a convert command. Also, having image format specific code in
>>> qemu-img is evil.
>> If I implement add-cow convert command, I am wondering which method should
>> I use:
>> 1) create add-cow, and its backing_file, and its image_file,  then we
>> need 3 files.
>> 2) create add-cow(with all bitmap marked to allocated), and its
>> image_file, then we
>>     need 2 files.
>> 2) will be easier, I should let .add-cow file can live only with
>> image_file, without backing_file.
>> I think both 1) and 2) need add code to qemu-img.c. Or I will have to create
>> image_file automaticly in add_cow_create function.
>> Can you give some comments on how to implement convert? Thanks.
> Just leave it alone and it will work.
> qemu-img convert takes the same options as qemu-img create. So like for
> any other image you specify the backing file with -b or -o backing_file,
> and for add-cow images to be successfully created you also need to
> specify -o image_file.
"-o image_file", the image_file should be precreated? Or I should created it
> Kevin

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