From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38018) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZCLmO-0002GF-Pj for qemu-devel@nongnu.org; Tue, 07 Jul 2015 01:50:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZCLmK-0008PB-OS for qemu-devel@nongnu.org; Tue, 07 Jul 2015 01:50:52 -0400 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:55233 helo=mx01.kamp.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZCLmK-0008OD-Dj for qemu-devel@nongnu.org; Tue, 07 Jul 2015 01:50:48 -0400 Message-ID: <559B68B2.5060402@kamp.de> Date: Tue, 07 Jul 2015 07:50:42 +0200 From: Peter Lieven MIME-Version: 1.0 References: <559ABE850200006600045FF0@relay2.provo.novell.com> <559A5B79.4010707@kamp.de> <559BA0D502000066000469BB@relay2.provo.novell.com> In-Reply-To: <559BA0D502000066000469BB@relay2.provo.novell.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] vpc size reporting problem List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Chun Yan Liu , qemu-devel@nongnu.org Cc: kwolf@redhat.com, mreitz@redhat.com Am 07.07.2015 um 03:50 schrieb Chun Yan Liu: > >>>> On 7/6/2015 at 06:42 PM, in message <559A5B79.4010707@kamp.de>, Peter Lieven > 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? 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