printk: Remove no longer used LOG_PREFIX.

When commit 5becfb1 ("kmsg: merge continuation records while
printing") introduced LOG_PREFIX, we used KERN_DEFAULT etc. as a flag
for setting LOG_PREFIX in order to tell whether to call cont_add()
(i.e. whether to append the message to "struct cont").

But since commit 4bcc595 ("printk: reinstate KERN_CONT for
printing continuation lines") inverted the behavior (i.e. don't append
the message to "struct cont" unless KERN_CONT is specified) and commit
5aa068e ("printk: remove games with previous record flags")
removed the last LOG_PREFIX check, setting LOG_PREFIX via KERN_DEFAULT
etc. is no longer meaningful.

Therefore, we can remove LOG_PREFIX and make KERN_DEFAULT empty string.

Link: http://lkml.kernel.org/r/1550829580-9189-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
To: Steven Rostedt <rostedt@goodmis.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>

include/linux/kern_levels.h

@@ -14,7 +14,7 @@
 #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 */
+#define KERN_DEFAULT	""		/* the default kernel loglevel */
 
 /*
  * Annotation for a "continued" line of log printout (only done after a

include/linux/printk.h

@@ -18,7 +18,6 @@ static inline int printk_get_level(const char *buffer)
 	if (buffer[0] == KERN_SOH_ASCII && buffer[1]) {
 		switch (buffer[1]) {
 		case '0' ... '7':
-		case 'd':	/* KERN_DEFAULT */
 		case 'c':	/* KERN_CONT */
 			return buffer[1];
 		}

kernel/printk/printk.c

@@ -345,7 +345,6 @@ static int console_msg_format = MSG_FORMAT_DEFAULT;
 
 enum log_flags {
 	LOG_NEWLINE	= 2,	/* text ended with a newline */
-	LOG_PREFIX	= 4,	/* text started with a prefix */
 	LOG_CONT	= 8,	/* text is a fragment of a continuation line */
 };
 
@@ -1922,9 +1921,6 @@ int vprintk_store(int facility, int level,
 			case '0' ... '7':
 				if (level == LOGLEVEL_DEFAULT)
 					level = kern_level - '0';
-				/* fallthrough */
-			case 'd':	/* KERN_DEFAULT */
-				lflags |= LOG_PREFIX;
 				break;
 			case 'c':	/* KERN_CONT */
 				lflags |= LOG_CONT;
@@ -1939,7 +1935,7 @@ int vprintk_store(int facility, int level,
 		level = default_message_loglevel;
 
 	if (dict)
-		lflags |= LOG_PREFIX|LOG_NEWLINE;
+		lflags |= LOG_NEWLINE;
 
 	return log_output(facility, level, lflags,
 			  dict, dictlen, text, text_len);