Mksquashfs: extend -root-time option to take date string

TIME can now be an unsigned 32-bit integer since the epoch of 1970-01-01
or a string value which is passed to the "date" command to parse.

Any string value which the date command recognises can be used such as
"now", "last week", Wed Feb 08 06:02:39" or "Wed Feb 15 21:02:39 GMT 2023".

Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>

squashfs-tools/mksquashfs.c

@@ -6178,10 +6178,13 @@ static void print_options(FILE *stream, char *name, int total_mem)
 	fprintf(stream, "be used such as \"now\", \"last\n\t\t\tweek\", or ");
 	fprintf(stream, "\"Wed Feb 15 21:02:39 GMT 2023\"\n");
 	fprintf(stream, "-root-time <time>\tset root directory time to ");
-	fprintf(stream, "<time>, which is an unsigned\n\t\t\t32-bit int ");
-	fprintf(stream, "indicating seconds since the epoch\n\t\t\t(1970-01-01)\n");
-	fprintf(stream, "-root-mode <mode>\tset root directory permissions to octal ");
-	fprintf(stream, "<mode>\n");
+	fprintf(stream, "<time>. <time> can be an\n\t\t\tunsigned 32-bit ");
+	fprintf(stream, "int indicating seconds since the epoch\n\t\t\t");
+	fprintf(stream, "(1970-01-01) or a string value which is passed to ");
+	fprintf(stream, "the\n\t\t\t\"date\" command to parse. Any string ");
+	fprintf(stream, "value which the date\n\t\t\tcommand recognises can ");
+	fprintf(stream, "be used such as \"now\", \"last\n\t\t\tweek\", or ");
+	fprintf(stream, "\"Wed Feb 15 21:02:39 GMT 2023\"\n");
 	fprintf(stream, "-root-uid <value>\tset root directory owner to ");
 	fprintf(stream, "specified <value>,\n\t\t\t<value> can be either an ");
 	fprintf(stream, "integer uid or user name\n");
@@ -7795,7 +7798,9 @@ int main(int argc, char *argv[])
 			}
 			root_gid_opt = TRUE;
 		} else if(strcmp(argv[i], "-root-time") == 0) {
-			if((++i == argc) || !parse_num_unsigned(argv[i], &root_time)) {
+			if((++i == argc) ||
+					(!parse_num_unsigned(argv[i], &root_time) &&
+					!exec_date(argv[i], &root_time))) {
 				ERROR("%s: -root-time missing or invalid time\n",
 					argv[0]);
 				exit(1);