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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 22:26:39 +0800

On Thu, Jun 14, 2012 at 10:24 PM, Kevin Wolf <address@hidden> wrote:
> Am 14.06.2012 16:17, schrieb Dong Xu Wang:
>> 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
>> manually?
> Yes, it must already exist. Just like with qemu-img create. To convert
> an existing qcow2 image that has a backing file 'base.img' to an add-cow
> image, you would use something like:
> $ qemu-img create -f raw target.img 4G
> $ qemu-img convert -O add-cow -o image_file=target.img -B base.img
> source.qcow2 target.add-cow
> Kevin
Got it, thanks

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