printk: clean up handling of log-levels and newlines

It used to be that we would only look at the log-level in a printk()
after explicit newlines, which can cause annoying problems when the
previous printk() did not end with a '\n'. In that case, the log-level
marker would be just printed out in the middle of the line, and be
seen as just noise rather than change the logging level.

This changes things to always look at the log-level in the first
bytes of the printout. If a log level marker is found, it is always
used as the log-level. Additionally, if no newline existed, one is
added (unless the log-level is the explicit KERN_CONT marker, to
explicitly show that it's a continuation of a previous line).
Acked-by: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kernel.h

@@ -102,7 +102,7 @@ extern const char linux_proc_banner[];
  * 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	""
+#define	KERN_CONT	"<c>"
 
 extern int console_printk[];
 

kernel/printk.c

@@ -687,20 +687,33 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 				  sizeof(printk_buf) - printed_len, fmt, args);
 
 
+	p = printk_buf;
+
+	/* Do we have a loglevel in the string? */
+	if (p[0] == '<') {
+		unsigned char c = p[1];
+		if (c && p[2] == '>') {
+			switch (c) {
+			case '0' ... '7': /* loglevel */
+				current_log_level = c - '0';
+				if (!new_text_line) {
+					emit_log_char('\n');
+					new_text_line = 1;
+				}
+			/* Fallthrough - skip the loglevel */
+			case 'c': /* KERN_CONT */
+				p += 3;
+				break;
+			}
+		}
+	}
+
 	/*
 	 * Copy the output into log_buf.  If the caller didn't provide
 	 * appropriate log level tags, we insert them here
 	 */
-	for (p = printk_buf; *p; p++) {
+	for ( ; *p; p++) {
 		if (new_text_line) {
-			/* If a token, set current_log_level and skip over */
-			if (p[0] == '<' && p[1] >= '0' && p[1] <= '7' &&
-			    p[2] == '>') {
-				current_log_level = p[1] - '0';
-				p += 3;
-				printed_len -= 3;
-			}
-
 			/* Always output the token */
 			emit_log_char('<');
 			emit_log_char(current_log_level + '0');