linux-kernel - Re: [Y2038] [PATCH 0/3] introduce new evdev interface type

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Date:	Thu, 03 Dec 2015 13:56:32 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	y2038@...ts.linaro.org
Cc:	Pingbo Wen <pingbo.wen@...aro.org>, linux-api@...r.kernel.org,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-kernel@...r.kernel.org, aksgarg1989@...il.com,
	linux-input@...r.kernel.org
Subject: Re: [Y2038] [PATCH 0/3] introduce new evdev interface type

On Thursday 03 December 2015 13:54:47 Arnd Bergmann wrote:
> > > struct input_event {
> > > #if !defined(__KERNEL__) && __TIME_T_BITS == __BITS_PER_LONG
> > >        struct timeval time;
> > 
> > > #else
> > >     struct {
> > >             union {
> > >                     __u32 tv_sec __attribute__((deprecated));
> > >                     __u32 tv_sec_monotonic;
> > >             };
> > >             __s32 tv_usec;
> > >     } time;
> > > #endif
> > >        __u16 type;
> > >        __u16 code;
> > >        __s32 value;
> > > };
> > 
> > I have one question here, if userspace use this structure, all helper functions
> > of timeval will not work. And userspace need to write extra helper function for
> > this fake timeval. This just create an another urgly time structure.
> 
> Correct, this is a useful side-effect of the change: any user space access to
> the event->time member that assumes it's a timeval will cause a compile-time
> warning or error (depending on the access), which helps us identify the
> broken code and fix it to use monotonic times as well as access the right
> struct members.
> 

To clarify, the code also intentionally only changes the types when
we are compiling with a new 32-bit libc: everything that builds today
will continue to build and work without warnings, unless it gets
recompiled with 64-bit time_t and needs to be fixed.

	Arnd
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