btrfs-progs: add duration format to fmt_print

Add "duration" format in seconds to fmt_print which will convert the
input to one of the following strings:

1. if number of seconds represents more than one day, the output will be
   for example: "1 days 01:30:00" (left the plural so parsing back the
   string is easier)
2. if less then a day: "23:30:10"

Author: Racz Zoltan <racz.zoli@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: raczzoli

Documentation/dev/dev-json.rst

@@ -14,6 +14,7 @@ Supported types:
 * size: ``size-or-none`` - same as *size* but for 0 it's *none*
 * UUID: ``uuid`` - if all zeros then *null* (native json), or properly formatted UUID string
 * date + time: ``date-time`` - timestamp formatted as *YYYY-MM-DD HH:MM:SS TIMEZONE*
+* duration: ``duration`` - difference of two timestamps, like *D days HH:MM:SS* (days not show of 0)
 
 Commands that support json output
 ---------------------------------

common/format-output.c

@@ -380,6 +380,17 @@ void fmt_print(struct format_ctx *fctx, const char* key, ...)
 		} else {
 			putchar('-');
 		}
+	} else if (strcmp(row->fmt, "duration") == 0) {
+		const u64 seconds = va_arg(args, u64);
+		unsigned int days = seconds / (24 * 60 * 60);
+		unsigned int hours = (seconds % (24 * 60 * 60)) / (60 * 60);
+		unsigned int minutes = (seconds % (60 * 60)) / 60;
+		unsigned int sec = seconds % 60;
+
+		if (days > 0)
+			printf("%u days %02u:%02u:%02u", days, hours, minutes, sec);
+		else
+			printf("%02u:%02u:%02u", hours, minutes, sec);
 	} else if (strcmp(row->fmt, "list") == 0) {
 	} else if (strcmp(row->fmt, "map") == 0) {
 	} else if (strcmp(row->fmt, "qgroupid") == 0) {