linux-kernel - Re: [RFC PATCH v1 5/7] media: v4l2: introduce two IOCTLs for face detection

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Date:	Tue, 6 Dec 2011 12:55:55 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Tony Lindgren <tony@...mide.com>, Greg KH <greg@...ah.com>,
	linux-kernel@...r.kernel.org,
	Sylwester Nawrocki <snjw23@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-omap@...r.kernel.org
Subject: Re: [RFC PATCH v1 5/7] media: v4l2: introduce two IOCTLs for face detection

On Tuesday 06 December 2011, Ming Lei wrote:
> diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
> index 073eb4d..8aeaa1e 100644
> --- a/include/linux/videodev2.h
> +++ b/include/linux/videodev2.h
> @@ -2214,7 +2214,12 @@ struct v4l2_fd_result {
>         __u32   buf_index;
>         __u32   face_cnt;
>         __u32   reserved[6];
> -       struct v4l2_fd_detection *fd;
> +
> +       /*make 64/32 compatible*/
> +       union {
> +               struct v4l2_fd_detection *fd;
> +               __u64   dummy;
> +       };
>  };
> 

That's not compatible, at least not on any big-endian architecture.
If you want to have an indirect pointer, you have to cast it to the
__u64 member in user space and back in kernel space.

Using an array added to the end of the v4l2_fd_result structure
rather than a pointer would really make this easier IMHO.

	Arnd
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