Re: [Qemu-devel] vpc size reporting problem

[Peter Lieven <pl@kamp.de>]

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 <559B6BBE.3050500@kamp.de>, Peter Lieven
>> <pl@kamp.de> wrote:
>>> Am 07.07.2015 um 07:59 schrieb Chun Yan Liu:
>>>>   
>>>>>>> On 7/7/2015 at 01:50 PM, in message <559B68B2.5060402@kamp.de>, Peter Lieven
>>>> <pl@kamp.de> wrote:
>>>>> Am 07.07.2015 um 03:50 schrieb Chun Yan Liu:
>>>>>>>>> On 7/6/2015 at 06:42 PM, in message <559A5B79.4010707@kamp.de>, Peter Lieven
>>>>>> <pl@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.
>>>    
>>> 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?

Peter