Re: [PATCH] Use qemu_memalign instead of qemu_malloc

[Anthony Liguori <aliguori@us.ibm.com>]

Kevin Wolf wrote:
> Anthony Liguori schrieb:
>   
>> Kevin Wolf wrote:
>>     
>>> Anthony Liguori schrieb:
>>>  
>>>       
>>>> I guess the main block code is not as defensive as I thought it was. 
>>>> This patch
>>>> uses qemu_memalign to allocate the buffers for IO so that you don't
>>>> get errors
>>>> when using O_DIRECT.
>>>>     
>>>>         
>>> Actually, the block code should be able to deal with unaligned buffers
>>> since qemu rev. 4599. This change seems to be present in current KVM.
>>>   
>>>       
>> That was what I thought at first too.
>>
>>     
>>> Can you tell exactly which operation failed?
>>>       
>> The aio requests fail with -22 (EINVAL).
>>     
>
> Yes, if it fails, the EINVAL is no surprise. I meant what code path it
> was using. Obviously we missed something in our patch and I'd like to
> fix that. Did the error occur on raw images or something like qcow2?
>   

It's a raw image and the calls are being made via 
bdrv_aio_read/bdrv_aio_write.  It doesn't occur with a qcow2 but then 
cache=off doesn't seem to do what it's supposed to with cache=off (I 
believe the underlying backing file is not opened O_DIRECT?).

Regards,

Anthony Liguori

> Kevin
>