Am 05.02.2013 11:54, schrieb Kevin Wolf: > Am 01.02.2013 22:51, schrieb Stefan Weil: >> 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. >> >> This patch fixes https://bugs.launchpad.net/qemu/+bug/1105670/. >> >> Signed-off-by: Stefan Weil <s...@weilnetz.de> >> --- >> block/vpc.c | 9 ++++----- >> 1 file changed, 4 insertions(+), 5 deletions(-) >> >> diff --git a/block/vpc.c b/block/vpc.c >> index fff103b..799b1c9 100644 >> --- a/block/vpc.c >> +++ b/block/vpc.c >> @@ -198,11 +198,10 @@ 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 an image in Virtual PC may depend on the geometry >> + * rather than on the size stored in the footer (the size in the footer >> + * is usually larger). Nevertheless we must use the real size here. */ >> + bs->total_sectors = be64_to_cpu(footer->size) / 512; >> >> /* Allow a maximum disk size of approximately 2 TB */ >> if (bs->total_sectors >= 65535LL * 255 * 255) { > Now VMs created with qemu can't be run in Virtual PC any more because > they use more space than is really visible on VPC.
Now VMs created with QEMU show the size which is also reported by MS tools. I don't think this is a problem. > The bug report doesn't say anything about practical consequences of the > unexpected behaviour, so I'd tend to claim that just the expectation was > wrong. Having to deal with two differing sizes is ugly, but we had the > discussion before and using the geometry was considered the least bad > way, because it gives you the same disk size within the VM as on Virtual PC. > > If you want to change it, you need to provide a real use case that breaks. > > Kevin Test case: * Create a VHD disk image (either with QEMU or MS tools). * Run a modern guest OS (which does not use CHS) on this image using Virtual PC or VirtualBox and write into the last disk blocks. * Copy the image to another format using qemu-img. => The last blocks are missing now. Stefan
