On Fri, Aug 18, 2017 at 6:09 PM, Andreas Dilger <adilger@xxxxxxxxx> wrote:
>
>>>> So moving to the case of a 32 bit machine:
>>>>
>>>> get_seconds() can return values until year 2106. And, recentcy at max
>>>> can only be 35. Analyzing the current line:
>>>>
>>>> if (dtime && (dtime < now) && (now < dtime + recentcy))
>>>>
>>>> The above equation should work fine at least until 35 seconds before
>>>> y2038 deadline.
>>>
>>> Since it's all unsigned arithmetic, it should be fine until 2106.
>>> However, we should get rid of get_seconds() long before then
>>> and use ktime_get_real_seconds() instead, as most other users
>>> of get_seconds() are (more) broken.
>>
>> Dtime on disk representation again breaks this for certain values in
>> 2038 even though everything is unsigned.
>>
>> I was just saying that whatever we do here depends on how dtime on
>> disk is interpreted.
>>
>> Agree that ktime_get_real_seconds() should be used here. But, the way
>> we handle new values would rely on this new interpretation of dtime.
>> Also, using time64_t variables on stack only matters after this. Once
>> the types are corrected, maybe the comparison expression need not
>> change at all (after new dtime interpretation is in place).
>
> There will not be a new dtime format on disk, but since the calculation
> here only depends on relative times (within a few minutes), then it would
> be fine to use only 32-bit timestamps, and truncate off the high bits
> from get_seconds()/ktime_get_real_seconds().
Agreed.
Are you planning to apply your fix for it then? I think your first
suggestion is all we need, aside from the three minor comments
I had.
Arnd
