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

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Date:	Mon, 24 Nov 2014 13:03:24 +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 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() ...

> --- a/include/uapi/linux/virtio_ring.h
> +++ b/include/uapi/linux/virtio_ring.h

>  /* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
>  struct vring_desc {
>         /* Address (guest-physical). */
> -       __u64 addr;
> +       __virtio64 addr;

... and __le64?

There's already lots of precedence or this, even in include/uapi/.

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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