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

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Date:	Fri, 02 Dec 2011 13:33:36 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Ming Lei <ming.lei@...onical.com>,
	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 Friday 02 December 2011 17:12:56 Ming Lei wrote:
> +/**
> + * struct v4l2_fd_result - VIDIOC_G_FD_RESULT argument
> + * @buf_index: entry, index of v4l2_buffer for face detection
> + * @face_cnt:  return, how many faces detected from the @buf_index
> + * @fd:                return, result of faces' detection
> + */
> +struct v4l2_fd_result {
> +       __u32   buf_index;
> +       __u32   face_cnt;
> +       __u32   reserved[6];
> +       struct v4l2_fd_detection *fd;
> +};


This data structure is not 32/64 bit safe: running a 64 bit kernel with 32 bit
user space will see an incompatible layout.

One way to solve this is to remove the pointer and just start the array
directly after the __u32 members. Alternatively, you can use a __u64
to pass the pointer in an integer representation.

A nicer interface from the data structure perspective would be to
get rid of the array altogether and always return exactly one face.

	Arnd
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