>>> On 7/7/2015 at 01:50 PM, in message <559b68b2.5060...@kamp.de>, Peter Lieven <p...@kamp.de> wrote: > Am 07.07.2015 um 03:50 schrieb Chun Yan Liu: > > > >>>> On 7/6/2015 at 06:42 PM, in message <559a5b79.4010...@kamp.de>, Peter > >>>> Lieven > > <p...@kamp.de> wrote: > >> Am 06.07.2015 um 11:44 schrieb Chun Yan Liu: > >>> While testing with a 1GB VHD file created on win7, found that the VHD > >>> file > >>> size reported on Windows is different from that is reported by qemu-img > >>> info or within a Linux KVM guest. > >>> > >>> Created a dynamic VHD file on win7, on Windows, it is reported 1024MB > >>> (2097152 sectors). But with qemu-img info or within a Linux KVM guest, > >>> it is reported 1023MB (2096640 sectors). > >>> > >>> The values in the footer_buf are as follows: > >>> creator_app: "win " > >>> cylinders: 0x820 (2080) > >>> heads: 0x10 (16) > >>> cyl/sec: 0x3f (63) > >>> current_size: 0x40000000 (1G) > >>> > >>> So, if using current_size, it's correct; but using CHS will get a smaller > >> size. > >>> Should we add a check in this case and use "current_size" instead of > >>> CHS? > >> > >> As far as I remember the issue was and still is that there is no official > >> spec that says > >> use current_size in case A and CHS in case B. > > Understand. > > > >> > >> If currrent_size is greater than CHS and Windows would use CHS (we don't > >> know that) we might run into issues if Qemu uses current_size. In this > >> cas we would write data beyond the end of the container (from Windows > >> perspective). > > That's right. The fact is in our testing we found Windows does not use CHS > > but current_size (from testing result), we create and get the VHD parted on > > Windows, then take the VHD file into Linux KVM guest, it fails to show > partition > > table (since the reported disk size is shrinking, some of the partitions > extend > > beyond the end of the disk). > > Which version of Windows are you referring to?
Tested with WS2012R2 and Win7. > > I personally think that it might be ok to use current_size if its greater > than the size derived from CHS. Our current implementation when > creating an image assumes we have to choose CHS to be equal > or greater to current_size. This can cause the same issue in the > other direction. > > Peter > >
