Re: [PATCH v2 3/4] input: Deprecate real timestamps beyond year 2106

On Thu, Oct 27, 2016 at 03:25:43PM -0700, Deepa Dinamani wrote:

quoted

quoted

struct timeval is not y2038 safe.
All usage of timeval in the kernel will be replaced by
y2038 safe structures.

struct input_event maintains time for each input event.
Real time timestamps are not ideal for input as this
time can go backwards as noted in the patch a80b83b7b8
by John Stultz. Hence, having the input_event.time fields
only big enough for monotonic and boot times are
sufficient.

Leave the original input_event as is. This is to maintain
backward compatibility with existing userspace interfaces
that use input_event.
Introduce a new replacement struct raw_input_event.
This replaces timeval with struct input_timeval. This structure
maintains time in __kernel_ulong_t or compat_ulong_t to allow
for architectures to override types as in the case of x32.

The change requires any userspace utilities reading or writing
from event nodes to update their reading format to match
raw_input_event. The changes to the popular libraries will be
posted along with the kernel changes.
The driver version is also updated to reflect the change in
event format.

If users are forced to update to adapt to the new event format, should
we consider more radical changes? For example, does it make sense to
send timestamp on every event? Maybe we should only send it once per
event packet (between EV_SYN/SYN_REPORT)? What granularity do we need?
Is there anything else in current protocol that we'd like to change?

I did see the thread with Pingbo's patches where you had a similar comment.

I see my series as decoupling the kernel input event format from the
userspace format.
The formats also are really the same still.
Could this be considered the first step towards changing the protocol?

I really do not see the point. I think we agree that the current
protocol is not working past 2038 and it does not seem we can fix it
transparently for the user. So we need to define new protocol and let
kernel and clients negotiate which one is used.

I am not concerned about in-kernel representation much as it does not
get stored anywhere so we can adjust it as needed without too much
effort.

The protocol changes might need new interfaces to be defined between libraries.
And, could end up being a substantial change.
Would a step by step approach make sense?

It would depend largely on the scope.

Thanks.

-- 
Dmitry
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