Re: [Qemu-devel] [RFC] qed: Add QEMU Enhanced Disk format

[Anthony Liguori]

On 09/06/2010 06:18 AM, Daniel P. Berrange wrote:
> I agree with ditching compression, but encryption is an important
> capability which cannot be satisfactorily added at other layers
> in the stack. While block devices / local filesystems can layer
> in dm-crypt in the host, this is not possible with network/cluster
> filesystems which account for a non-trivial target audience.

ecryptfs should work with NFS these days.  If it still doesn't, it will 
in the not too distant future.

>   Adding
> encryption inside the guest is sub-optimal because you cannot do
> secure automation of guest startup. Either you require manaual
> intervention to start every guest to enter the key, or if you
> hardcode the key, then anyone who can access the guest disk image
> can start the guest.

I think this belongs in the VFS level but from a format perspective, an 
encryption feature would be easy to add.

> > +
> > +        if ((s->header.compat_features&  QED_CF_BACKING_FORMAT)) {
> > +            ret = qed_read_string(bs->file, s->header.backing_fmt_offset,
> > +                                  s->header.backing_fmt_size,
> > +                                  bs->backing_format,
> > +                                  sizeof(bs->backing_format));
> > +            if (ret<  0) {
> > +                return ret;
> > +            }
> > +        }
> >      
> IMHO we should make the backing format compulsory with use of
> the backing file. The only time probing is required is when
> initially creating the child image, thereafter there's no
> benefit to probing again.
>    

Stefan originally made it mandatory but I asked to make it optional.

From a format specification perspective, backing_fmt introduces some 
problems.  What does a backing_fmt of 'vmdk' mean outside of qemu?

More importantly, humans to create image formats by hand.  Instead, they 
use tools like qemu-img.  If you think we should for the specification 
of a backing file format in qemu-img, that's the place we should do it.

Regards,

Anthony Liguori

> Regards,
> Daniel
>