Am 08.02.2013 13:14, schrieb Jeff Cody: > On Fri, Feb 08, 2013 at 09:38:47AM +0100, Kevin Wolf wrote: >> 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"?
Linux is a modern OS per definition :-) I made an additional test with Knoppix (from December 2006), and it worked as expected. >> >> 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 > Kevin, > > I can test this on Virtual PC on a Win 7 install, as well as > Hyper-V (I've already tested the equivalent of this patch on Hyper-V > on Windows Server 2012). I'll do some testing today with this - if > you have anything in particular you want me to look at, just let me > know. > > Stefan, did you test if this behaves the same for all disk sizes, or > only for larger disk sizes of 127G and up? This behaves the same in a test with a small (16 MiB) image. Regards, Stefan W.
