linux-kernel - Re: [PATCH RFC v2 01/16] virtio: memory access APIs

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Date:	Wed, 22 Oct 2014 13:45:55 -0400
From:	Christopher Covington <cov@...eaurora.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	"Lad, Prabhakar" <prabhakar.csengg@...il.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	David Drysdale <drysdale@...gle.com>,
	Piotr Król <piotr.krol@...eb.com>,
	Bjarke Istrup Pedersen <gurligebis@...too.org>,
	Anup Patel <anup.patel@...aro.org>,
	virtualization@...ts.linux-foundation.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH RFC v2 01/16] virtio: memory access APIs

Hi Michael,

On 10/22/2014 11:50 AM, Michael S. Tsirkin 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 will (in the
> future) query device endian-ness and act accordingly.
> 
> At the moment, stub them out and assume native endian-ness everywhere.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  include/linux/virtio_config.h    | 16 +++++++++++++
>  include/uapi/linux/virtio_ring.h | 49 ++++++++++++++++++++--------------------
>  include/uapi/linux/Kbuild        |  1 +
>  3 files changed, 42 insertions(+), 24 deletions(-)
> 
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index 7f4ef66..d38d3c2 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -4,6 +4,7 @@
>  #include <linux/err.h>
>  #include <linux/bug.h>
>  #include <linux/virtio.h>
> +#include <linux/virtio_byteorder.h>

What patch creates this file?

>  #include <uapi/linux/virtio_config.h>
>  
>  /**
> @@ -152,6 +153,21 @@ int virtqueue_set_affinity(struct virtqueue *vq, int cpu)
>  	return 0;
>  }
>  
> +/* Memory accessors */
> +#define DEFINE_VIRTIO_XX_TO_CPU(bits) \
> +static inline u##bits virtio##bits##_to_cpu(struct virtio_device *vdev, __virtio##bits val) \
> +{ \
> +	return __virtio##bits##_to_cpu(false, val); \
> +} \
> +static inline __virtio##bits cpu_to_virtio##bits(struct virtio_device *vdev, u##bits val) \
> +{ \
> +	return __cpu_to_virtio##bits(false, val); \
> +}
> +
> +DEFINE_VIRTIO_XX_TO_CPU(16)
> +DEFINE_VIRTIO_XX_TO_CPU(32)
> +DEFINE_VIRTIO_XX_TO_CPU(64)
> +
>  /* Config space accessors. */
>  #define virtio_cread(vdev, structname, member, ptr)			\
>  	do {								\
> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
> index a99f9b7..6c00632 100644
> --- a/include/uapi/linux/virtio_ring.h
> +++ b/include/uapi/linux/virtio_ring.h
> @@ -32,6 +32,7 @@
>   *
>   * Copyright Rusty Russell IBM Corporation 2007. */
>  #include <linux/types.h>
> +#include <linux/virtio_types.h>
>  
>  /* This marks a buffer as continuing via the next field. */
>  #define VRING_DESC_F_NEXT	1
> @@ -61,32 +62,32 @@
>  /* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
>  struct vring_desc {
>  	/* Address (guest-physical). */
> -	__u64 addr;
> +	__virtio64 addr;
>  	/* Length. */
> -	__u32 len;
> +	__virtio32 len;
>  	/* The flags as indicated above. */
> -	__u16 flags;
> +	__virtio16 flags;
>  	/* We chain unused descriptors via this, too */
> -	__u16 next;
> +	__virtio16 next;
>  };

How does __virtio64 differ from __le64?

Thanks,
Chris

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