linux-kernel - Re: [PATCH v3 04/41] virtio: memory access APIs

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Date:	Mon, 24 Nov 2014 13:58:43 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>, cornelia.huck@...ibm.com,
	rusty@....ibm.com, Nicholas Bellinger <nab@...ux-iscsi.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Pranavkumar Sawargaonkar <pranavkumar@...aro.org>,
	Anup Patel <anup.patel@...aro.org>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Bjarke Istrup Pedersen <gurligebis@...too.org>,
	stephen hemminger <stephen@...workplumber.org>,
	virtualization@...ts.linux-foundation.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v3 04/41] virtio: memory access APIs

On Mon, Nov 24, 2014 at 1:15 PM, Michael S. Tsirkin <mst@...hat.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@...hat.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"?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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
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