Am 07.02.2013 20:26, schrieb Stefan Weil: > From: Stefan Weil <stefan@kiwi.(none)> > > The size calculated from the CHS values is not the real image (disk) size, > but usually a smaller value. This is caused by rounding effects. > > Only older operating systems use CHS. Such guests won't be able to use > the whole disk. All modern operating systems use the real size. > > This patch fixes https://bugs.launchpad.net/qemu/+bug/1105670/. > > Signed-off-by: Stefan Weil <s...@weilnetz.de> > --- > > This is a rebased extract from my patch series for block/vpc.c. > It's the minimum needed to fix the open bug for QEMU 1.4. > > The rest of the series can be discussed and applied after 1.4. > > Regards > > Stefan W. > > PS. Please excuse a previous personal mail which I had sent > with a wrong signature and without addressing qemu-devel. > > block/vpc.c | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) > > diff --git a/block/vpc.c b/block/vpc.c > index 82229ef..b4ff564 100644 > --- a/block/vpc.c > +++ b/block/vpc.c > @@ -34,6 +34,8 @@ > > #define HEADER_SIZE 512 > > +#define VHD_SECTOR_SIZE 512 > + > //#define CACHE > > enum vhd_type { > @@ -204,11 +206,13 @@ static int vpc_open(BlockDriverState *bs, int flags) > /* Write 'checksum' back to footer, or else will leave it with zero. */ > footer->checksum = be32_to_cpu(checksum); > > - // The visible size of a image in Virtual PC depends on the geometry > - // rather than on the size stored in the footer (the size in the footer > - // is too large usually) > - bs->total_sectors = (int64_t) > - be16_to_cpu(footer->cyls) * footer->heads * footer->secs_per_cyl; > + /* The visible size of a image in Virtual PC depends on the guest: > + * QEMU and other emulators report the real size (here in sectors). > + * All modern operating systems use this real size. > + * Very old operating systems use CHS values to calculate the total size. > + * This calculated size is usually smaller than the real size. > + */ > + bs->total_sectors = be64_to_cpu(footer->size) / VHD_SECTOR_SIZE;
It's unfortunate that I don't have my old Virtual PC installation around any more so I could prove that you're wrong for at least some versions. Or does a Linux of 2009 already count as "very old"? If we want to commit this - and I still feel uncomfortable about it - then maybe it's best to remove the comment altogether instead of making such claims. The new code is the intuitively expected one anyway. Kevin
