Re: [Qemu-devel] [PATCH v5 1/8] virtio_get_byteswap: function for endian-ambivalent targets using virtio

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

On Tue, 25 Feb 2014 16:21:21 +0100
Stefan Hajnoczi <stefanha@redhat.com> wrote:
> On Fri, Feb 21, 2014 at 12:28:11PM +0100, Greg Kurz wrote:
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index aeabf3a..4fd6ac2 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -19,6 +19,9 @@
> >  #include "hw/virtio/virtio.h"
> >  #include "qemu/atomic.h"
> >  #include "hw/virtio/virtio-bus.h"
> > +#include "hw/virtio/virtio-access.h"
> > +
> > +bool virtio_byteswap;
> >  
> >  /*
> >   * The alignment to use between consumer and producer parts of vring.
> > @@ -546,6 +549,9 @@ void virtio_reset(void *opaque)
> >  
> >      virtio_set_status(vdev, 0);
> >  
> > +    /* We assume all devices are the same endian. */
> > +    virtio_byteswap = virtio_get_byteswap();
> > +
> >      if (k->reset) {
> >          k->reset(vdev);
> >      }
> 
> In the previous version it was pointed out that the global is nasty.
> 
> A cleaner solution is a per-VirtIODevice enum device_endian value which
> gets passed to lduw_phys_internal()/stl_phys_internal()/etc.
> 
> Now the same code can be used for:
> 1. Host == guest-endian
> 2. Host != guest-endian
> 3. "Everything is little-endian" (VIRTIO 1.0)
> 
> Keeping it per-device means we can have both legacy and VIRTIO 1.0
> devices in a guest.
> 
> That's better than hacking in a global now and having to undo it when
> VIRTIO 1.0 support gets merged.
> 
> Stefan
> 

Stefan,

I was unsure whether people wanted that global (nasty indeed) to be kicked
out of the picture right now or later. Things are clearer now. :)
I will come back with something more appropriate.

Thanks for your time.

Regards.

-- 
Gregory Kurz                                     kurzgreg@fr.ibm.com
                                                 gkurz@linux.vnet.ibm.com
Software Engineer @ IBM/Meiosys                  http://www.ibm.com
Tel +33 (0)562 165 496

"Anarchy is about taking complete responsibility for yourself."
        Alan Moore.