dmesg: implement official '-r' and colored output '-C'

Actually there is no way to have the level with the DMESG_PRETTY
-r option (raw format) is present for that in debian systems

The optional -C allow a colored output for both configs
this parameter is inspired from android logcat one.

Behavior is kept (default is raw if DMESG_PRETTY config is not set)

Signed-off-by: Tanguy Pruvot <tanguy.pruvot@gmail.com>
diff --git a/util-linux/dmesg.c b/util-linux/dmesg.c
index 6505da5..14051b5 100644
--- a/util-linux/dmesg.c
+++ b/util-linux/dmesg.c
@@ -10,16 +10,24 @@
  */
 
 //usage:#define dmesg_trivial_usage
-//usage:       "[-c] [-n LEVEL] [-s SIZE]"
+//usage:       "[-c] [-n LEVEL] [-r] [-s SIZE] [-C]"
 //usage:#define dmesg_full_usage "\n\n"
 //usage:       "Print or control the kernel ring buffer\n"
 //usage:     "\n	-c		Clear ring buffer after printing"
 //usage:     "\n	-n LEVEL	Set console logging level"
+//usage:     "\n	-r		Show level prefix"
 //usage:     "\n	-s SIZE		Buffer size"
+//usage:     "\n	-C		Colored output"
 
 #include <sys/klog.h>
 #include "libbb.h"
 
+#define COLOR_DEFAULT 0
+#define COLOR_WHITE   231
+#define COLOR_YELLOW  226
+#define COLOR_ORANGE  166
+#define COLOR_RED     196
+
 int dmesg_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int dmesg_main(int argc UNUSED_PARAM, char **argv)
 {
@@ -29,11 +37,13 @@
 	enum {
 		OPT_c = 1 << 0,
 		OPT_s = 1 << 1,
-		OPT_n = 1 << 2
+		OPT_n = 1 << 2,
+		OPT_r = 1 << 3,
+		OPT_C = 1 << 4
 	};
 
 	opt_complementary = "s+:n+"; /* numeric */
-	opts = getopt32(argv, "cs:n:", &len, &level);
+	opts = getopt32(argv, "cs:n:rC", &len, &level);
 	if (opts & OPT_n) {
 		if (klogctl(8, NULL, (long) level))
 			bb_perror_msg_and_die("klogctl");
@@ -55,13 +65,37 @@
 		return EXIT_SUCCESS;
 
 
-	if (ENABLE_FEATURE_DMESG_PRETTY) {
+	if ((ENABLE_FEATURE_DMESG_PRETTY || (opts & OPT_C)) && !(opts & OPT_r)) {
 		int last = '\n';
-		int in = 0;
+		int in = 0, l, color;
+		char pfx[16], *lvl;
 
 		/* Skip <#> at the start of lines */
 		while (1) {
 			if (last == '\n' && buf[in] == '<') {
+				if (opts & OPT_C) {
+					lvl = buf + in + 1;
+					sscanf(lvl, "%d", &level);
+
+					switch (level) {
+					case 1:
+					case 2:
+					case 3: color = COLOR_RED;    break;
+					case 4: color = COLOR_ORANGE; break;
+					case 5: color = COLOR_YELLOW; break;
+					case 7: color = COLOR_WHITE;  break;
+					case 6: // common dmesg info
+					default: color = COLOR_DEFAULT;
+					}
+
+					if (color != COLOR_DEFAULT)
+						l = sprintf(pfx, "%c[%d;%d;%dm",
+							0x1B, 38, 5, color);
+					else
+						l = sprintf(pfx, "%c[%dm", 0x1B, 0);
+
+					full_write(STDOUT_FILENO, pfx, l);
+				}
 				in += 3;
 				if (in >= len)
 					break;
@@ -72,9 +106,17 @@
 			if (in >= len)
 				break;
 		}
+
+		if (opts & OPT_C) {
+			/* Reset default terminal color */
+			l = sprintf(pfx, "%c[%dm", 0x1B, 0);
+			full_write(STDOUT_FILENO, pfx, l);
+		}
+
 		/* Make sure we end with a newline */
 		if (last != '\n')
 			bb_putchar('\n');
+
 	} else {
 		full_write(STDOUT_FILENO, buf, len);
 		if (buf[len-1] != '\n')