Re: [Qemu-devel] [PATCH] virtio: move bi-endian target support to a single location

[Paolo Bonzini <pbonzini@redhat.com>]

On 03/06/2016 03:16, David Gibson wrote:
> On Thu, Jun 02, 2016 at 06:04:37PM +0200, Greg Kurz wrote:
>> On Wed, 1 Jun 2016 12:33:28 +1000
>> David Gibson <david@gibson.dropbear.id.au> wrote:
>>
>>> On Tue, May 31, 2016 at 03:15:21PM +0200, Paolo Bonzini wrote:
>>>>
>>>>
>>>> On 31/05/2016 15:10, Greg Kurz wrote:  
>>>>>>>>> +#if defined(TARGET_PPC64) || defined(TARGET_ARM)
>>>>>>>>> +#define LEGACY_VIRTIO_IS_BIENDIAN 1
>>>>>>>>> +#endif    
>>>>>>>
>>>>>>> These will only be correct if something else includes cpu.h.  Instead of  
>>>>> Unless I missed something, the TARGET_* macros come from the generated
>>>>> config-target.h header, which is in turn included by qemu/osdep.h and
>>>>> thus included by most of the code.  
>>>>
>>>> You're right.  Problems _could_ happen if virtio-access.h is included in
>>>> a file compiled without -DNEED_CPU_H (i.e. with common-obj-y instead of
>>>> obj-y) but include/exec/poison.h should take care of that.
>>>>   
>>>>>>> defining this, you should add
>>>>>>>
>>>>>>> #include "cpu.h"
>>>>>>>
>>>>>>> at the top of include/hw/virtio-access.h and leave the definitions in
>>>>>>> target-*/cpu.h.
>>>>>>>   
>>>>> All this bi-endian stuff is really an old-virtio-only thing... it is
>>>>> only to be used by virtio_access_is_big_endian(). The fact that it
>>>>> broke silently with your cleanup series is yet another proof that
>>>>> this workaround is fragile.  
>>>>
>>>> It is not fragile actually.  cpu.h doesn't exist in common-obj-y, so the
>>>> TARGET_IS_BIENDIAN define can be safely taken from cpu.h.
>>>>
>>>> Anyway because of poison.h your solution isn't fragile either, so
>>>>
>>>> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>  
>>>
>>> Should I take this through my tree?
>>>
>>
>> That would be great !
> 
> Actually, that was a question for Paolo..

It would be more of a question for mst; I do not maintain virtio (that's
why I wrote R-b and not Acked-by).

Thanks,

Paolo