lib/vsprintf: Add specifier for printing struct timespec64

A handful drivers want to print a content of the struct timespec64
in a format of %lld:%09ld. In order to make their lives easier, add
the respecting specifier directly to the printf() implementation.

Signed-off-by: Andy Shevchenko <[e-mail]>
Reviewed-by: Petr Mladek <[e-mail]>
Tested-by: Petr Mladek <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Petr Mladek <[e-mail]>

Documentation/core-api/printk-formats.rst

···
 	%pt[RT]s		YYYY-mm-dd HH:MM:SS
 	%pt[RT]d		YYYY-mm-dd
 	%pt[RT]t		HH:MM:SS
-	%pt[RT][dt][r][s]
+	%ptSp			<seconds>.<nanoseconds>
+	%pt[RST][dt][r][s]
 
 For printing date and time as represented by::
 
-	R  struct rtc_time structure
+	R  content of struct rtc_time
+	S  content of struct timespec64
 	T  time64_t type
 
 in human readable format.
···
 The %pt[RT]s (space) will override ISO 8601 separator by using ' ' (space)
 instead of 'T' (Capital T) between date and time. It won't have any effect
 when date or time is omitted.
+
+The %ptSp is equivalent to %lld.%09ld for the content of the struct timespec64.
+When the other specifiers are given, it becomes the respective equivalent of
+%ptT[dt][r][s].%09ld. In other words, the seconds are being printed in
+the human readable format followed by a dot and nanoseconds.
 
 Passed by reference.
 

lib/tests/printf_kunit.c

···
 	};
 	/* 2019-01-04T15:32:23 */
 	time64_t t = 1546615943;
+	struct timespec64 ts = { .tv_sec = t, .tv_nsec = 11235813 };
 
 	test("(%pt?)", "%pt", &tm);
 	test("2018-11-26T05:35:43", "%ptR", &tm);
···
 	test("0119-00-04 15:32:23", "%ptTsr", &t);
 	test("15:32:23|2019-01-04", "%ptTts|%ptTds", &t, &t);
 	test("15:32:23|0119-00-04", "%ptTtrs|%ptTdrs", &t, &t);
+
+	test("2019-01-04T15:32:23.011235813", "%ptS", &ts);
+	test("1546615943.011235813", "%ptSp", &ts);
 }
 
 static void

lib/vsprintf.c

···
 }
 
 static noinline_for_stack
+char *timespec64_str(char *buf, char *end, const struct timespec64 *ts,
+		     struct printf_spec spec, const char *fmt)
+{
+	static const struct printf_spec default_dec09_spec = {
+		.base = 10,
+		.field_width = 9,
+		.precision = -1,
+		.flags = ZEROPAD,
+	};
+
+	if (fmt[2] == 'p')
+		buf = number(buf, end, ts->tv_sec, default_dec_spec);
+	else
+		buf = time64_str(buf, end, ts->tv_sec, spec, fmt);
+	if (buf < end)
+		*buf = '.';
+	buf++;
+
+	return number(buf, end, ts->tv_nsec, default_dec09_spec);
+}
+
+static noinline_for_stack
 char *time_and_date(char *buf, char *end, void *ptr, struct printf_spec spec,
 		    const char *fmt)
 {
 	switch (fmt[1]) {
 	case 'R':
 		return rtc_str(buf, end, (const struct rtc_time *)ptr, spec, fmt);
+	case 'S':
+		return timespec64_str(buf, end, (const struct timespec64 *)ptr, spec, fmt);
 	case 'T':
 		return time64_str(buf, end, *(const time64_t *)ptr, spec, fmt);
 	default:
···
  * - 'd[234]' For a dentry name (optionally 2-4 last components)
  * - 'D[234]' Same as 'd' but for a struct file
  * - 'g' For block_device name (gendisk + partition number)
- * - 't[RT][dt][r][s]' For time and date as represented by:
+ * - 't[RST][dt][r][s]' For time and date as represented by:
  *      R    struct rtc_time
+ *      S    struct timespec64
  *      T    time64_t
+ * - 'tSp' For time represented by struct timespec64 printed as <seconds>.<nanoseconds>
  * - 'C' For a clock, it prints the name (Common Clock Framework) or address
  *       (legacy clock framework) of the clock
  * - 'G' For flags to be printed as a collection of symbolic strings that would