Re: [Xen-devel] why are qemu-img and vhd-util created files incompatible?

[Andrei Lifchits <andrei.lifchits@xxxxxxxxxx>]

On Sun, Feb 17, 2013 at 2:30 PM, Darren Shepherd
<darren.s.shepherd@xxxxxxxxx> wrote:
> I was wondering if someone can shed some light on why vhd files
> created with qemu-img don't really work right with vhd-util and
> consequentially blktap in general.  To validate the incompatiblity its
> simple enough to do
>
> qemu-img create -f vpc test.vhd 40g
> vhd-util snapshot -n child.vhd -p test.vhd
>
> Which will show the below and then the headers don't display the BATMAP 
> summary:
>
> primary footer invalid: creation time in future

This is due to a bug in the blktap2 code which uses local time instead
of UTC (which is mandated by the VHD specs). I fixed it recently in
the Citrix fork of blktap
(https://github.com/xen-org/blktap/commit/a79ac2c05f97c2384bbf981419f329f184dc646a),
but unfortunately these two forks aren't really kept in sync.

> test.vhd appears invalid; dumping metadata
> Failed to open test.vhd: -22
>
> Additionally "vhd-util snapshot -n child.vhd -p test.vhd" will give
> you the same 22 error.
>
> I was going to start researching this with the eventual goal of
> changing qemu-img, but I thought I'd ask the experts first.
>
> Thanks,
> Darren
>
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