linux-kernel - Re: [PATCH v4 6/8] media: v4l2-core: fix v4l2

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Date:   Tue, 26 Nov 2019 16:17:01 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>
Subject: Re: [PATCH v4 6/8] media: v4l2-core: fix v4l2_buffer handling for
 time64 ABI

On Tue, Nov 26, 2019 at 3:15 PM Hans Verkuil <hverkuil@...all.nl> wrote:
>
> Then use that in the struct v4l2_buffer definition:
>
> struct v4l2_buffer {
> ...
> #ifdef __KERNEL__
>         struct __kernel_v4l2_timeval timestamp;
> #else
>         struct timeval               timestamp;
> #endif
>
> That keeps struct v4l2_buffer fairly clean. And it also makes it
> possible to have a bit more extensive documentation for the
> struct __kernel_v4l2_timeval without polluting the actual struct
> v4l2_buffer definition.

Yes, good idea. I've added this version now:

#ifdef __KERNEL__
/*
 * This corresponds to the user space version of timeval
 * for 64-bit time_t. sparc64 is different from everyone
 * else, using the microseconds in the wrong half of the
 * second 64-bit word.
 */
struct __kernel_v4l2_timeval {
        long long       tv_sec;
#if defined(__sparc__) && defined(__arch64__)
        int             tv_usec;
        int             __pad;
#else
        long long       tv_usec;
#endif
};
#endif

I briefly considered using #else #define __kernel_v4l2_timeval timeval
to avoid the second #ifdef, but went back to your version again
for clarify.

> The videodev2.h header is something users of the API look at a
> lot and having this really ugly kernel timestamp in there is
> not acceptably IMHO. But splitting it off should work.

Do you also mean moving it into a separate header file, or
just outside of struct v4l2_buffer? Since it's hidden in #ifdef
__KERNEL__, it could be moved to media/ioctl.h or elsewhere.

      Arnd