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

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Date:   Thu, 08 Jun 2017 22:42:40 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        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>
Subject: Re: [PATCH v1 04/25] lib/vsprintf: Print time and date in human readable format via %pt

On Thu, Jun 08 2017, Andy Shevchenko <andy.shevchenko@...il.com> wrote:

> On Thu, Jun 8, 2017 at 9:41 PM, Alexandre Belloni
> <alexandre.belloni@...e-electrons.com> wrote:
>> 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:
>
>>> > 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.
>
> Yeah, but the problem is to pass the reference. All dances around will
> uglify the code.
> (Obviously we can't pass timespec64/time64_t or anything longer than
> 32 bits as is in %p extension)
>

I like that this gets rid of some mm/dd/yy and other more or less random
format and ends up standardizing yyyy-mm-dd HH:MM:SS. However, I do
think %pt should take either ktime_t or timespec64 (obviously by
reference), with fx these options

[ir] ISO (yyyy-mm-dd HH:MM:SS) or raw (seconds since epoch)
[n] append nanoseconds (.%09ld).

Please don't give people the option of eliding either the time or the
date; I've spent too much time dealing with syslog files that don't
include the year in the timestamps.

Getting a timespec64* or ktime_t* from <something else> is not that
bad. There's the compound literal option

#define rtc_tm2timespec64p(tm) \
 (&(struct timespec64){ .tv_sec = rtc_tm_to_time64(tm), .tv_nsec = 0 })

printk("%pt", rtc_tm2timespec64p(tm))

or the two-extra-lines per call-site

struct timespec64 ts;
rtc_tm2time64(tm, &ts)
printk("%pt", &ts)


Rasmus