Re: [Y2038] Which type to use for timestamps: u64 or s64?

[Hans Verkuil <hverkuil@xs4all.nl>]

On 11/05/15 09:36, Arnd Bergmann wrote:
> On Thursday 05 November 2015 08:41:11 Hans Verkuil wrote:
>> Hi Arnd,
>>
>> We're redesigning the timestamp handling in the video4linux subsystem moving away
>> from struct timeval to a single timestamp in ns (what ktime_get_ns() gives us).
>> But I was wondering: ktime_get_ns() gives a s64, so should we use s64 as well as
>> the timestamp type we'll eventually be returning to the user, or should we use u64?
>>
>> The current patch series we made uses a u64, but I am now beginning to doubt that
>> decision.
> 
> I would lean towards u64, but I don't think it really matters either way,
> especially since all the drivers should be using monotonic timestamps now.

One thing that might be easier if it is a s64 is when adding/subtracting offsets
from the timestamp. And the other reason is that a u64 gives a false view of the
underlying type. With a s64 it is clear that a timestamp will wrap around after
292 years instead of double that. Admittedly, not our problem, but if we ever send
a space probe to Alpha Centauri, then it might be nice to know as application
developer that you need to take special measures if the mission takes longer than
292 years :-)

Regards,

	Hans