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: <20170608184154.y7tqsv7ghpbcbf77@piout.net>
Date:   Thu, 8 Jun 2017 20:41:54 +0200
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        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>,
        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 08/06/2017 at 20:57:05 +0300, Andy Shevchenko wrote:
> On Thu, Jun 8, 2017 at 6:05 PM, Alexandre Belloni
> <alexandre.belloni@...e-electrons.com> wrote:
> > On 08/06/2017 at 17:55:12 +0300, Andy Shevchenko 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? For struct tm it's somelike 4 (which want to print its content).
> >>
> >> > 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.
> >> Verify tm_year member carefully.
> >>
> >
> > I understand this may not fit your debugging needs but what about pretty
> > printing time64_t and using rtc_tm_to_time64?
> 
> There are two downsides as I can see:
> 1) conversion to and from just for that;

Those are almost all debug messages, I would be fine with that.

> 2) if you look closer to the patches rtc-* you may find cases where
> wday is also printed so, struct rtc_time still will be in use.
> 

(And you missed two in rtc-mcp795.c). Honestly, nobody cares about wday,
you may as well leave it out.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com