lkml.org 
[lkml]   [2014]   [Nov]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 04/41] virtio: memory access APIs
On Mon, Nov 24, 2014 at 01:58:43PM +0100, Geert Uytterhoeven wrote:
> On Mon, Nov 24, 2014 at 1:15 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Mon, Nov 24, 2014 at 01:03:24PM +0100, Geert Uytterhoeven wrote:
> >> On Mon, Nov 24, 2014 at 12:52 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> >> > virtio 1.0 makes all memory structures LE, so
> >> > we need APIs to conditionally do a byteswap on BE
> >> > architectures.
> >> >
> >> > To make it easier to check code statically,
> >> > add virtio specific types for multi-byte integers
> >> > in memory.
> >> >
> >> > Add low level wrappers that do a byteswap conditionally, these will be
> >> > useful e.g. for vhost. Add high level wrappers that
> >> > query device endian-ness and act accordingly.
> >>
> >> > diff --git a/include/linux/virtio_byteorder.h b/include/linux/virtio_byteorder.h
> >> > new file mode 100644
> >> > index 0000000..824ed0b
> >> > --- /dev/null
> >> > +++ b/include/linux/virtio_byteorder.h
> >>
> >> > +static inline u16 __virtio16_to_cpu(bool little_endian, __virtio16 val)
> >> > +{
> >> > + if (little_endian)
> >> > + return le16_to_cpu((__force __le16)val);
> >> > + else
> >> > + return (__force u16)val;
> >> > +}
> >>
> >> What's wrong with just using le16-to_cpu() ...
> >
> > le16-to_cpu() is simply wrong: virtio needs to be
> > LE or native endian, depending on whether it's running
> > in 0.9 or 1.0 mode.
>
> IC, that was not clear from the description for this patch.
> I thought it was dependent on BE architectures.
>
> Nevertheless, any chance you can get rid of the "conditional"?

I don't see how - this is fundamental to any virtio device
that wants to support both 0.9 and 1.0 from the same
codebase.

> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
> -- Linus Torvalds


\
 
 \ /
  Last update: 2014-11-24 20:21    [W:0.115 / U:0.224 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site