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Date: Fri, 28 Mar 2008 13:22:48 +0100
From: Jiri Slaby <jirislaby@gmail.com>
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To: Andi Kleen <andi@firstfloor.org>
CC: Mauro Carvalho Chehab <mchehab@infradead.org>,
       Linux and Kernel Video <video4linux-list@redhat.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: v4l & compat_ioctl
References: <47ECD0CF.1020003@gmail.com> <87y783jdjo.fsf@basil.nowhere.org> <47ECD715.90507@gmail.com> <20080328113803.GQ29105@one.firstfloor.org>
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On 03/28/2008 12:38 PM, Andi Kleen wrote:
> BTW i haven't audited them, but if there is u64 or similar in there anywhere
> be careful about alignment.

Well, not good, some ioctls have different numbers on 32 and 64 bit:
struct v4l2_ext_controls {
         __u32 ctrl_class;
         __u32 count;
         __u32 error_idx;
         __u32 reserved[2];
         struct v4l2_ext_control *controls;
};
#define VIDIOC_G_EXT_CTRLS      _IOWR ('V', 71, struct v4l2_ext_controls)
as an example.

And alignment is a problem here (v4l2_std_id is u64):
struct v4l2_standard {
         __u32                index;
         v4l2_std_id          id;
         __u8                 name[24];
         struct v4l2_fract    frameperiod; /* Frames, not fields */
         __u32                framelines;
         __u32                reserved[4];
};
which results in different ioctl numbers too.