Re: linux-aio usable?

[Michael Tokarev <mjt@tls.msk.ru>]

Avi Kivity wrote:
> On 03/08/2010 10:19 PM, Michael Tokarev wrote:
>> Michael Tokarev wrote:
>> []
>>   
>>> Apparently that does not quite work.  I just re-compiled kvm with
>>> --enable-linux-aio (actually I just installed libaio-dev on debian
>>> and qemu-kvm's configure picked it up automatically), and tried
>>> a guest.  But any I/O fails.
>>>      
>> It has nothing to do with kvm.  It is compat_ioctl32 in the kernel
>> wrt aio calls.  Historically I've a 64bit kernel with 32bit userland,
>> and tried 32bit kvm too, and that does not work.  But 64bit kvm works
>> just fine with aio, and the performance numbers are indeed better.
> 
> Can you elaborate?  This sounds like a bug that wants to be fixed.

http://thread.gmane.org/gmane.linux.kernel.aio.general/2891

It's missing compat_ioctl for some of the aio opcodes, namely
it's PREADV and PWRITE - the only ones used by kvm and the only
ones missing in kernel.

As far as i can see, current code converts the iocb array just
fine, but does not touch iovec array used with p{read,write}v.

/mjt