Re: [Qemu-devel] qemu: block.c: introducing "fmt:FMT:" prefix to image-filenames

[Anthony Liguori <anthony@codemonkey.ws>]

Daniel P. Berrange wrote:
> On Thu, Jan 08, 2009 at 08:15:25PM +0200, Uri Lublin wrote:
>   
>> The purpose of this prefix is to
>> 1. Provide a way to know the backing file format without probing
>>    it (setting the format upon creation time).
>> 2. Enable using qcow2 format (and others) over host block devices.
>>    (only if the user specifically asks for it).
>>
>> If no fmt:FMT: is provided we go back to probing.
>>     
>
> I still don't like the fact that this is inventing a second syntax
> for specifying format that's different to the syntax used for  the 
> existing -drive parameter, which is
>
>   -drive file=/some/path,format=qcow2,....other disk options...
>
>   
>> backing file format is qcow2 (even though it's on a host block device)
>> $ qemu-img create -b fmt:qcow2:/dev/loop0 -f qcow2 /tmp/uuu.qcow2
>>     
>
> I'd prefer to see a '-F' flag to specify format of backing file and
> leave syntax of existing -b arg alone
>
>  $ qemu-img create -F qcow2 -b /dev/loop0 -f qcow2 /tmp/uuu.qcow2
>   

You may have multiple backing images.  I don't see how you can do fix 
this without encoding the information in the path, or changing qcow2.

Regards,

Anthony Liguori

>> force backing file format to raw (no probing)
>> $ qemu-img create -f raw /tmp/image1.raw 10G
>> $ qemu-img create -b fmt:raw:/tmp/image1.raw -f qcow2 /tmp/image1.qcow2
>>     
>
>   $ qemu-img create -F raw -b /tmp/image1.raw -f qcow2 /tmp/image1.qcow2
>
>   
>> Use together with other protocols, e.g. nbd
>> $ qemu-nbd -v -n --snapshot -t -k /tmp/uuu.socket 
>> fmt:qcow2:/tmp/images/uuu.qcow2 &
>>     
>
> Should just add  a -f arg to qemu-nbd to specify format so it
> follows qemu-img style, eg
>
>  $ qemu-nbd -v -n --snapshot -t -k /tmp/uuu.socket \
>     -f qcow2 /tmp/images/uuu.qcow2 &
>
>   
>> $ qemu-img info nbd:unix:/tmp/uuu.socket
>> $ qemu-system-x86_64 -snapshot -hda nbd:unix:/tmp/uuu.socket
>>
>> Or fat
>> $ qemu-system-x86_64 -hda fmt:qcow2:/tmp/uuu.qcow2 -hdb 
>> fat:floppy:/tmp/images
>>     
>
> This is unneccessary, since -hda is deprecated, and there's a 
> new -drive arg that already has ability to set format explicitly,
> as well as many other flags that you need when setting up disks.
>
>    $ qemu-system-x86_64 \ 
>          -drive index=0,format=qcow2,file=/tmp/uuu.qcow2 \
>          -drive index=1,format=fat:floppy,file=/tmp/images
>
> Regards,
> Daniel
>