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

[Kevin Wolf <kwolf@redhat.com>]

Am 14.06.2012 16:06, schrieb Dong Xu Wang:
> On Thu, Jun 14, 2012 at 6:51 PM, Kevin Wolf <kwolf@redhat.com> 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 <wdongxu@linux.vnet.ibm.com>
>>
>> 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.

Kevin