Re: raw disks no longer work in latest kvm (kvm-88 was fine)

[Antoine Martin <antoine@nagafix.co.uk>]

On 05/23/2010 06:57 PM, Avi Kivity wrote:
> On 05/23/2010 11:53 AM, Antoine Martin wrote:
>> I'm not: 64-bit host and 64-bit guest.
>> Just to be sure, I've tested that patch and still no joy:
>>   /dev/vdc: read failed after 0 of 512 at 0: Input/output error
>>   /dev/vdc: read failed after 0 of 512 at 0: Input/output error
>>   /dev/vdc: read failed after 0 of 2048 at 0: Input/output error
>> pread is still broken on this big raw disk.
>>
>
> Can you summarize your environment and reproducer again?  The thread 
> is so long it is difficult to understand exactly what you are testing.
>
Sure thing:

Description of the problem:
A guest tries to mount a large raw partition (1.5TB /dev/sda9 in my 
case), this fails with pread enabled, works with it disabled.

What has been tested:
Host has had 2.6.31.x and now 2.6.34 - with no improvement.
Guest has had numerous kernel versions and patches applied for testing 
(from 2.6.31.x to 2.6.34) - none made any difference. (although the 
recent patch stopped the large partition from getting corrupted by the 
merged requests bug.. yay!)
It was once thought that glibc needed to be rebuilt against newer kernel 
headers, done that too, and rebuilt qemu-kvm afterwards. (was 2.6.28 
then 2.6.31 and now 2.6.33)

What has been reported: straces, kernel error messages as above.
Here is the qemu command line (sanitized - removed the virtual disks 
which work fine and network config):
qemu -clock dynticks -m 256 -L ./ -kernel ./bzImage-2.6.34-aio -append 
"root=/dev/vda" -nographic -drive file=/dev/sda9,if=virtio,cache=none

Let me know if you need any other details. I can also arrange ssh access 
to the system if needed.

Cheers
Antoine