Re: [PATCH] Use qemu_memalign instead of qemu_malloc

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

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).

> But apart from that, qemu_memalign is the right thing to do, because
> copying from/into an aligned buffer in the block code costs performance
> (don't know how much, though).
>   

Regards,

Anthony Liguori

> Kevin
>