linux-kernel - Re: [PATCH v4 05/42] virtio: memory access APIs

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Date:	Tue, 25 Nov 2014 18:42:38 +0100
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
	rusty@....ibm.com, nab@...ux-iscsi.org, pbonzini@...hat.com,
	Rusty Russell <rusty@...tcorp.com.au>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Bjarke Istrup Pedersen <gurligebis@...too.org>,
	stephen hemminger <stephen@...workplumber.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	virtualization@...ts.linux-foundation.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v4 05/42] virtio: memory access APIs

On Tue, 25 Nov 2014 18:41:42 +0200
"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.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  include/linux/virtio_byteorder.h  | 59 +++++++++++++++++++++++++++++++++++++++
>  include/linux/virtio_config.h     | 32 +++++++++++++++++++++
>  include/uapi/linux/virtio_ring.h  | 45 ++++++++++++++---------------
>  include/uapi/linux/virtio_types.h | 48 +++++++++++++++++++++++++++++++
>  include/uapi/linux/Kbuild         |  1 +
>  5 files changed, 163 insertions(+), 22 deletions(-)
>  create mode 100644 include/linux/virtio_byteorder.h
>  create mode 100644 include/uapi/linux/virtio_types.h
> 
> 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
> @@ -0,0 +1,59 @@
> +#ifndef _LINUX_VIRTIO_BYTEORDER_H
> +#define _LINUX_VIRTIO_BYTEORDER_H
> +#include <linux/types.h>
> +#include <uapi/linux/virtio_types.h>
> +
> +/*
> + * Memory accessors for handling virtio in modern little endian and in

"Low-level memory accessors"?

> + * compatibility native endian format.
> + */
(...)
> diff --git a/include/uapi/linux/virtio_types.h b/include/uapi/linux/virtio_types.h
> new file mode 100644
> index 0000000..b90385f
> --- /dev/null
> +++ b/include/uapi/linux/virtio_types.h
> @@ -0,0 +1,48 @@
> +#ifndef _UAPI_LINUX_VIRTIO_TYPES_H
> +#define _UAPI_LINUX_VIRTIO_TYPES_H
> +/* An interface for efficient virtio implementation, currently for use by KVM
> + * and lguest, but hopefully others soon.  

You probably copied this from the existing virtio header, didn't you?

What about simply:

"Type definitions for virtio implementations."

(and then the remaining text)

> Do NOT change this since it will
> + * break existing servers and clients.
> + *
> + * This header is BSD licensed so anyone can use the definitions to implement
> + * compatible drivers/servers.
(...)

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