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

[Uri Lublin]

Daniel P. Berrange wrote:
> On Thu, Jan 08, 2009 at 09:09:08PM +0200, Uri Lublin wrote:
> > 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
> > I can easily modify qemu-img to support -F.
> > The question is how to represent it such that when we run qemu it "knows" 
> > the backing file format. In other words what will '-F qcow2' do ? In this 
> > solution it will add 'fmt:qcow2:' as a prefix to the backing-file filename.
>
> 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 ...'

Thanks,
   Uri.