Re: [PATCH v1 04/25] lib/vsprintf: Print time and date in human readable format via %pt

[Arnd Bergmann]

On Thu, Jun 8, 2017 at 4:55 PM, Andy Shevchenko
<andy.shevchenko@xxxxxxxxx> wrote:
> On Thu, Jun 8, 2017 at 5:49 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
>> On Thu, Jun 8, 2017 at 3:47 PM, Andy Shevchenko
>> <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>>> There are users which print time and date represented by content of
>>> struct rtc_time in human readable format.
>>>
>>> Instead of open coding that each time introduce %pt[dt][rv] specifier.
>>
>> I really like the idea, and the implementation seems fine for this use case, but
>> before we reserve %pt for rtc_time, could we discuss whether we want
>> that for printing struct tm, struct timespec64, time64_t or ktime_t instead?
>
> How many users?

It's hard to predict, I would assume we get more users once there is an
easy way to print the time.

> For struct tm it's somelike 4 (which want to print its content).

Good point. I notice that they all convert from time64_t or time_t into
struct tm immediately before printing it, so we can scratch that one
as long as there is a way to pretty-print a time64_t. We also don't
need to print a time_t as we want to kill that one off anyway.

If we only care about printing time64_t and rtc_time, we can easily
use %pT for one and %pt for the other, but there may still be good
reasons to print a timespec64 or ktime_t.

>> I can see good reasons for pretty-printing any of them, but the namespace for
>> format strings is rather limited.
>>
>> struct rtc_time is almost the same as struct tm (the former has one extra
>> member), so maybe we can actually define them to be the same and
>> use one format string for both?
>
> The reason I decide to drop struct tm for now due to they are not
> compatible and I have got an interesting bugs.

Ok.

        Arnd