Re: [Qemu-devel] [PATCH] vpc: Fix size in fixed image creation

[Kevin Wolf <kwolf@redhat.com>]

Am 11.02.2015 um 23:32 hat Max Reitz geschrieben:
> On 2015-02-11 at 11:22, Kevin Wolf wrote:
> 
>     If total_sectors is rounded to match the geometry, total_size needs to
>     be changed as well. Otherwise we end up with an image whose geometry
>     describes a disk larger than the image file, which doesn't end well.
> 
>     Signed-off-by: Kevin Wolf <kwolf@redhat.com>
>     ---
>      block/vpc.c | 10 +++-------
>      1 file changed, 3 insertions(+), 7 deletions(-)
> 
> 
> Looks fine to me, but the spec says: "When the user creates a hard disk of a
> certain size, the size of the hard disk image in the virtual machine is smaller
> than that created by the user. This is because CHS value calculated from the
> hard disk size is rounded down."
> 
> So, well, qemu has been violating the specification all along, I guess.

Initially we rounded the size down. This ended up truncating images
during qemu-img convert, so it was decided that rounding up is the less
bad solution.

> So, with that in mind (that nobody has been screaming so far):
> 
> Reviewed-by: Max Reitz <mreitz@redhat.com>

Thanks!

> Alternatively we may want to "fix" it, and actually let the CHS size be smaller
> than total_sectors/total_size, if that's possible. But maybe that'll be even
> worse, so I'm fine either way.

That's possible. With VHD, however, I wouldn't make any such changes
without proof that some software needs it and other software isn't
affected. This is all pretty fragile.

Kevin