Re: [Qemu-devel] [PATCH] Warn if a qcow (not qcow2) file is opened

[Daniel P. Berrange]

On Tue, Jun 30, 2009 at 03:21:24PM +0100, Paul Brook wrote:
> > >>> The qcow block driver format is no longer maintained and likely
> > >>> contains
> > >>> serious data corruptors.  Urge users to stay away for it, and advertise
> > >>> the new and improved replacement.
> > >
> > > I'm not sure how I feel about this.  Can we prove qcow is broken?  Is
> > > it only broken for writes and not reads?
> >
> > Well, Kevin posted a patch, so it is.  It's definitely unmaintained.
> > Given it's a qemu native format, there is no interoperability value
> > except with old qemu versions.
> >
> > > If we're printing a warning, does that mean we want to deprecate qcow
> > > and eventually remove it (or remove write support, at least)?
> >
> > Yes.
> 
> IMHO there's little value in just printing a warning. Until it actually goes 
> away, people are liable to assume we're just being paranoid/awkward and keep 
> using it anyway.
>
> I suggest crippling it now and, assuming noone steps up to fix+maintain it, 
> ripping out the write support altogether at next release.
> I'm assuming the readonly code is in better shape, and can be supported with 
> relatively little effort.

I agree, if we want to phase it out we should be more discouraging than
just an ignoreable warning

 - Disable it in  qemu, and have code which looks for qcow1 magic
   bytes, prints an error message telling them to use qemu-img
   to convert to qcow2 and exits
 - Keep qcow1 in qemu-img as a source format only, to allow conversions
   to qcow2


Possibly have a 'configure' arg to let people re-enable full read-write
it if they badly need it, but tell them it'll be gone permanently in 
release qemu-0.12.0

Daniel
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