linux-kernel - Re: [PATCH v2 01/21] lib/vsprintf: Print time and date in human readable format via %pt

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Date:   Tue, 20 Feb 2018 15:55:07 -0800
From:   Joe Perches <joe@...ches.com>
To:     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@...r.kernel.org,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        linux-rtc@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Mark Salyzyn <salyzyn@...roid.com>
Cc:     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 v2 01/21] lib/vsprintf: Print time and date in human
 readable format via %pt

On Tue, 2018-02-20 at 23:43 +0200, Andy Shevchenko 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 %ptR[dt][rv] specifier.
> 
> Note, users have to select PRINTK_PEXT_TIMEDATE option in a Kconfig.

Not sure this is a great option.
Not just the name, the need to select it.

> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
[]
> +static noinline_for_stack
> +char *date_str(char *buf, char *end, const struct rtc_time *tm, bool v, bool r)
> +{
> +	int year = tm->tm_year + (r ? 0 : 1900);
> +	int mon = tm->tm_mon + (r ? 0 : 1);

What happens with negative values?
Perhaps these temporaries should be unsigned int.

> +
> +	if (unlikely(v && (unsigned int)tm->tm_year > 200))
> +		buf = string(buf, end, "****", default_str_spec);
> +	else
> +		buf = number(buf, end, year, default_dec04_spec);
> +
> +	if (buf < end)
> +		*buf = '-';
> +	buf++;
> +
> +	if (unlikely(v && (unsigned int)tm->tm_mon > 11))
> +		buf = string(buf, end, "**", default_str_spec);
> +	else
> +		buf = number(buf, end, mon, default_dec02_spec);
> +
> +	if (buf < end)
> +		*buf = '-';
> +	buf++;
> +
> +	if (unlikely(v && (unsigned int)tm->tm_mday > 31))
> +		buf = string(buf, end, "**", default_str_spec);
> +	else
> +		buf = number(buf, end, tm->tm_mday, default_dec02_spec);
> +
> +	return buf;
> +}
> +
> +static noinline_for_stack
> +char *time_str(char *buf, char *end, const struct rtc_time *tm, bool v, bool r)
> +{

Maybe use unsigned int temporaries here too for hour, min, sec

> +	if (unlikely(v && (unsigned int)tm->tm_hour > 24))
> +		buf = string(buf, end, "**", default_str_spec);
> +	else
> +		buf = number(buf, end, tm->tm_hour, default_dec02_spec);
> +
> +	if (buf < end)
> +		*buf = ':';
> +	buf++;
> +
> +	if (unlikely(v && (unsigned int)tm->tm_min > 59))

leap seconds are allowed in the struct

> +		buf = string(buf, end, "**", default_str_spec);
> +	else
> +		buf = number(buf, end, tm->tm_min, default_dec02_spec);
> +
> +	if (buf < end)
> +		*buf = ':';
> +	buf++;
> +
> +	if (unlikely(v && (unsigned int)tm->tm_sec > 59))
> +		buf = string(buf, end, "**", default_str_spec);
> +	else
> +		buf = number(buf, end, tm->tm_sec, default_dec02_spec);
> +
> +	return buf;
> +}
>