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 21:11:08 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Arnd Bergmann <arnd@...db.de>
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 Tue, Dec 6, 2011 at 8:55 PM, Arnd Bergmann <arnd@...db.de> wrote:
> 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.

Looks like it is a bit ugly.

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

I have tried to do this, but video_usercopy needs a few changes
to handle array args if no indirect pointer is passed to kernel.

I am not sure if media guys are happy to accept the changes, :-)

thanks,
--
Ming Lei
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