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

[Uri Lublin]

Kevin Wolf wrote:
> Jamie Lokier schrieb:
> > Uri Lublin wrote:
> > > Daniel P. Berrange wrote:
> > > > Yes the format you write into the qcow2 header can still use the 
> > > > fmt:qcow2: prefix - just no need to expose that particular qcow2
> > > > specific implementation detail on the CLI. 
> > > OK. I'll prepare a patch that adds '-F fmt' to 'qemu-img create -b ...'
> > Will it break backing files whose filename begins with "fmt:"?
> >
> > Just because I hate hidden "some filenames work, some filenames break
> > mysteriously, and of course it's not documented" dodgy hacks.
>
> Uri, now that you are making the change in qcow2 instead of block.c,
> have you thought about using the earlier suggested "filename.img\0qcow2"
> hack? This shouldn't break filenames.

Hi Kevin,

1. The change is still in block.c, as the backing file is opened in 
bdrv_open2(), and also we must support raw format as a backing_file format (and 
basically any format).
2. I thought everyone agreed that "filename.img\0qcow2" would work, but that we 
should try a different solution.
3. This patch does not make things worse (with regards to "unsupported 
filename"). Without it too, qemu will refuse to run a filename that begins with 
"fmt:"

Thanks,
    Uri.