Re: [Qemu-devel] [PATCH 3/5] vpc: Ignore geometry for large images

[Peter Lieven]

Am 23.02.2015 um 19:34 schrieb Max Reitz:
> On 2015-02-23 at 09:27, Peter Lieven wrote:
> > From: Kevin Wolf <address@hidden>
> >
> > The CHS calculation as done per the VHD spec imposes a maximum image
> > size of ~127 GB. Real VHD images exist that are larger than that.
> >
> > Apparently there are two separate non-standard ways to achieve this:
> > You could use more heads than the spec does - this is the option that
> > qemu-img create chooses.
> >
> > However, other images exist where the geometry is set to the maximum
> > (65536/16/255), but the actual image size is larger. Until now, such
> > images are truncated at 127 GB when opening them with qemu.
> >
> > This patch changes the vpc driver to ignore geometry in this case and
> > only trust the size field in the header.
> >
> > Signed-off-by: Kevin Wolf <address@hidden>
> > ---
> >   block/vpc.c |   10 ++++------
> >   1 file changed, 4 insertions(+), 6 deletions(-)
>
> I'm trusting you this works for disk2vhd; at least it's in accordance with the 
> VHD specification.

When I wrote the hack for disk2vhd some time ago I just found that the reported 
size was too big.
I was not aware that it was exactly this special value.

You say in the specs. Do you have a spec that is actually stating that 
(65536/16/255) is special
value that says ignore CHS and look at the footer?

Peter