printk: convert the format for KERN_<LEVEL> to a 2 byte pattern

Instead of "<.>", use an ASCII SOH for the KERN_<LEVEL> prefix initiator.

This saves 1 byte per printk, thousands of bytes in a normal kernel.

No output changes are produced as vprintk_emit converts these uses to
"<.>".

Signed-off-by: Joe Perches <[email protected]>
Cc: Kay Sievers <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: JoePerches

include/linux/kern_levels.h

@@ -1,22 +1,25 @@
 #ifndef __KERN_LEVELS_H__
 #define __KERN_LEVELS_H__
 
-#define KERN_EMERG	"<0>"	/* system is unusable			*/
-#define KERN_ALERT	"<1>"	/* action must be taken immediately	*/
-#define KERN_CRIT	"<2>"	/* critical conditions			*/
-#define KERN_ERR	"<3>"	/* error conditions			*/
-#define KERN_WARNING	"<4>"	/* warning conditions			*/
-#define KERN_NOTICE	"<5>"	/* normal but significant condition	*/
-#define KERN_INFO	"<6>"	/* informational			*/
-#define KERN_DEBUG	"<7>"	/* debug-level messages			*/
+#define KERN_SOH	"\001"		/* ASCII Start Of Header */
+#define KERN_SOH_ASCII	'\001'
+
+#define KERN_EMERG	KERN_SOH "0"	/* system is unusable */
+#define KERN_ALERT	KERN_SOH "1"	/* action must be taken immediately */
+#define KERN_CRIT	KERN_SOH "2"	/* critical conditions */
+#define KERN_ERR	KERN_SOH "3"	/* error conditions */
+#define KERN_WARNING	KERN_SOH "4"	/* warning conditions */
+#define KERN_NOTICE	KERN_SOH "5"	/* normal but significant condition */
+#define KERN_INFO	KERN_SOH "6"	/* informational */
+#define KERN_DEBUG	KERN_SOH "7"	/* debug-level messages */
+
+#define KERN_DEFAULT	KERN_SOH "d"	/* the default kernel loglevel */
 
-/* Use the default kernel loglevel */
-#define KERN_DEFAULT	"<d>"
 /*
  * Annotation for a "continued" line of log printout (only done after a
  * line that had no enclosing \n). Only to be used by core/arch code
  * during early bootup (a continued line is not SMP-safe otherwise).
  */
-#define KERN_CONT	"<c>"
+#define KERN_CONT	KERN_SOH "c"
 
 #endif

include/linux/printk.h

@@ -9,7 +9,7 @@ extern const char linux_proc_banner[];
 
 static inline int printk_get_level(const char *buffer)
 {
-	if (buffer[0] == '<' && buffer[1] && buffer[2] == '>') {
+	if (buffer[0] == KERN_SOH_ASCII && buffer[1]) {
 		switch (buffer[1]) {
 		case '0' ... '7':
 		case 'd':	/* KERN_DEFAULT */
@@ -27,7 +27,7 @@ static inline const char *printk_skip_level(const char *buffer)
 		case '0' ... '7':
 		case 'd':	/* KERN_DEFAULT */
 		case 'c':	/* KERN_CONT */
-			return buffer + 3;
+			return buffer + 2;
 		}
 	}
 	return buffer;