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Re: [Qemu-devel] [PATCH] vpc: Fix size in fixed image creation
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH] vpc: Fix size in fixed image creation |
Date: |
Thu, 12 Feb 2015 10:50:42 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
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 <address@hidden>
> ---
> 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 <address@hidden>
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