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

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Message-ID: <CAK8P3a3P4rDqQaNmBR9C9nF3VCqcQOH06Nq8RyDHsNfc0Ms13g@mail.gmail.com>
Date:   Thu, 8 Jun 2017 17:33:42 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        linux-rtc@...r.kernel.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Guan Xuetao <gxt@...c.pku.edu.cn>,
        Ingo Molnar <mingo@...nel.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        Jonathan Corbet <corbet@....net>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Thierry Reding <thierry.reding@...il.com>
Subject: Re: [PATCH v1 04/25] lib/vsprintf: Print time and date in human
 readable format via %pt

On Thu, Jun 8, 2017 at 4:55 PM, Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Thu, Jun 8, 2017 at 5:49 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> On Thu, Jun 8, 2017 at 3:47 PM, Andy Shevchenko
>> <andriy.shevchenko@...ux.intel.com> 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