Input: extend usable life of event timestamps to 2106 on 32 bit systems

The input events use struct timeval to store event time, unfortunately
this structure is not y2038 safe and is being replaced in kernel with
y2038 safe structures.

Because of ABI concerns we can not change the size or the layout of
structure input_event, so we opt to re-interpreting the 'seconds' part
of timestamp as an unsigned value, effectively doubling the range of
values, to year 2106.

Newer glibc that has support for 32 bit applications to use 64 bit
time_t supplies __USE_TIME_BITS64 define [1], that we can use to present
the userspace with updated input_event layout. The updated layout will
cause the compile time breakage, alerting applications and distributions
maintainers to the issue. Existing 32 binaries will continue working
without any changes until 2038.

Ultimately userspace applications should switch to using monotonic or
boot time clocks, as realtime clock is not very well suited for input
event timestamps as it can go backwards (see a80b83b7b8 "Input: evdev -
add CLOCK_BOOTTIME support" by by John Stultz). With monotonic clock the
practical range of reported times will always fit into the pair of 32
bit values, as we do not expect any system to stay up for a hundred
years without a single reboot.

[1] https://sourceware.org/glibc/wiki/Y2038ProofnessDesign

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Acked-by: Peter Hutterer <peter.hutterer@who-t.net>
Patchwork-Id: 10148083
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h
index 8c5a0bf6ee35..7288a7c573cc 100644
--- a/include/uapi/linux/input.h
+++ b/include/uapi/linux/input.h
@@ -21,10 +21,21 @@
 
 /*
  * The event structure itself
+ * Note that __USE_TIME_BITS64 is defined by libc based on
+ * application's request to use 64 bit time_t.
  */
 
 struct input_event {
+#if (__BITS_PER_LONG != 32 || !defined(__USE_TIME_BITS64)) && !defined(__KERNEL)
 	struct timeval time;
+#define input_event_sec time.tv_sec
+#define input_event_usec time.tv_usec
+#else
+	__kernel_ulong_t __sec;
+	__kernel_ulong_t __usec;
+#define input_event_sec  __sec
+#define input_event_usec __usec
+#endif
 	__u16 type;
 	__u16 code;
 	__s32 value;