Re: [Qemu-devel] vpc size reporting problem

[Chun Yan Liu]

>>> On 7/7/2015 at 02:36 PM, in message <address@hidden>, Peter Lieven
<address@hidden> wrote: 
> Am 07.07.2015 um 08:34 schrieb Chun Yan Liu: 
> > 
> >>>> On 7/7/2015 at 02:19 PM, in message <559B6F79.237 : 102 : 21807>, Chun 
> >>>> Yan  
> Liu 
> > wrote: 
> >>    
> >>>>> On 7/7/2015 at 02:03 PM, in message <address@hidden>, Peter Lieven 
> >> <address@hidden> wrote: 
> >>> Am 07.07.2015 um 07:59 schrieb Chun Yan Liu: 
> >>>>    
> >>>>>>> On 7/7/2015 at 01:50 PM, in message <address@hidden>, Peter Lieven 
> >>>> <address@hidden> wrote: 
> >>>>> Am 07.07.2015 um 03:50 schrieb Chun Yan Liu: 
> >>>>>>>>> On 7/6/2015 at 06:42 PM, in message <address@hidden>, Peter Lieven 
> >>>>>> <address@hidden> 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. 
> >>>     
> >>> Which storage driver? 
> > And imported to a Win7 guest on KVM as IDE device, it's also reported as 
> > 1024MB (not CHS value, CHS is 1023MB). 
>  
> And what storage driver reports 1023MB under Qemu? 

SCSI driver under Linux guest.

>  
> Peter
>  
>  
>  
>