[libvirt] backing file chains, -blockdev, and storage file autodetection

[Daniel P. Berrangé]

On Wed, Jan 08, 2020 at 03:34:02PM +0000, Martin Wilck wrote:
> Hi Peter,
> 
> On Wed, 2020-01-08 at 15:46 +0100, Peter Krempa wrote:
> > On Wed, Jan 08, 2020 at 13:34:14 +0000, Martin Wilck wrote:
> > > The recent change in libvirt to pass storage arguments to qemu via 
> > > "-blockdev", explicity passing backing file chain information
> > > rather
> > > than relying on qemu to figure it out, has bitten me quite
> > > painfully.

snip

> > In libvirt we already always record the image format when creating
> > the
> > overlay for many years now.
> 
> Unfortunately almost all tutorials about backing chains on the web just
> teach qemu-img usage. In my case I guess it's just an old habit.

I wonder if there's any scope for improving qemu-img here so that it
can 'do the right thing', or at least issue a warning if the suer
doesn't set a backing format. 


Regards,
Daniel
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