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

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

On 05/23/2010 09:18 PM, Avi Kivity wrote:
> On 05/23/2010 05:07 PM, Antoine Martin wrote:
>> 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.
>
> Did you mean: preadv?
Yes, here's what makes it work ok (as suggested by Christoph earlier in 
the thread) in posix-aio-compat.c:
#undef CONFIG_PREADV
#ifdef CONFIG_PREADV
static int preadv_present = 1;
#else
static int preadv_present = 0;
#endif
>>
>> 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.
>
> And: 64-bit host kernel, 64-bit host userspace, yes?
Yes. (and 64-bit guest/userspace too)
>
> Does aio=native help?
It does indeed!
>   How about if=ide?
Will test with another kernel and report back (this one doesn't have any 
non-virtio drivers)

Thanks
Antoine