printk: re-organize log_output() to be more legible

Avoid some duplicate logic now that we can return early, and update the
comments for the new LOG_CONT world order.

This also stops the continuation flushing from just using random record
flags for the flushing action, instead taking the flags from the proper
original line and updating them as we add continuations to it.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/printk/printk.c

@@ -1640,35 +1640,33 @@ static struct cont {
 	bool flushed:1;			/* buffer sealed and committed */
 } cont;
 
-static void cont_flush(enum log_flags flags)
+static void cont_flush(void)
 {
 	if (cont.flushed)
 		return;
 	if (cont.len == 0)
 		return;
-
 	if (cont.cons) {
 		/*
 		 * If a fragment of this line was directly flushed to the
 		 * console; wait for the console to pick up the rest of the
 		 * line. LOG_NOCONS suppresses a duplicated output.
 		 */
-		log_store(cont.facility, cont.level, flags | LOG_NOCONS,
+		log_store(cont.facility, cont.level, cont.flags | LOG_NOCONS,
 			  cont.ts_nsec, NULL, 0, cont.buf, cont.len);
-		cont.flags = flags;
 		cont.flushed = true;
 	} else {
 		/*
 		 * If no fragment of this line ever reached the console,
 		 * just submit it to the store and free the buffer.
 		 */
-		log_store(cont.facility, cont.level, flags, 0,
+		log_store(cont.facility, cont.level, cont.flags, 0,
 			  NULL, 0, cont.buf, cont.len);
 		cont.len = 0;
 	}
 }
 
-static bool cont_add(int facility, int level, const char *text, size_t len)
+static bool cont_add(int facility, int level, enum log_flags flags, const char *text, size_t len)
 {
 	if (cont.len && cont.flushed)
 		return false;
@@ -1679,7 +1677,7 @@ static bool cont_add(int facility, int level, const char *text, size_t len)
 	 * the line gets too long, split it up in separate records.
 	 */
 	if (nr_ext_console_drivers || cont.len + len > sizeof(cont.buf)) {
-		cont_flush(LOG_CONT);
+		cont_flush();
 		return false;
 	}
 
@@ -1688,7 +1686,7 @@ static bool cont_add(int facility, int level, const char *text, size_t len)
 		cont.level = level;
 		cont.owner = current;
 		cont.ts_nsec = local_clock();
-		cont.flags = 0;
+		cont.flags = flags;
 		cont.cons = 0;
 		cont.flushed = false;
 	}
@@ -1696,8 +1694,15 @@ static bool cont_add(int facility, int level, const char *text, size_t len)
 	memcpy(cont.buf + cont.len, text, len);
 	cont.len += len;
 
+	// The original flags come from the first line,
+	// but later continuations can add a newline.
+	if (flags & LOG_NEWLINE) {
+		cont.flags |= LOG_NEWLINE;
+		cont_flush();
+	}
+
 	if (cont.len > (sizeof(cont.buf) * 80) / 100)
-		cont_flush(LOG_CONT);
+		cont_flush();
 
 	return true;
 }
@@ -1732,39 +1737,26 @@ static size_t cont_print_text(char *text, size_t size)
 
 static size_t log_output(int facility, int level, enum log_flags lflags, const char *dict, size_t dictlen, char *text, size_t text_len)
 {
-	if (!(lflags & LOG_NEWLINE)) {
 	/*
-		 * Flush the conflicting buffer. An earlier newline was missing,
-		 * or another task also prints continuation lines.
+	 * If an earlier line was buffered, and we're a continuation
+	 * write from the same process, try to add it to the buffer.
 	 */
-		if (cont.len && (!(lflags & LOG_CONT) || cont.owner != current))
-			cont_flush(LOG_NEWLINE);
-
-		/* buffer line if possible, otherwise store it right away */
-		if (cont_add(facility, level, text, text_len))
+	if (cont.len) {
+		if (cont.owner == current && (lflags & LOG_CONT)) {
+			if (cont_add(facility, level, lflags, text, text_len))
 				return text_len;
-
-		return log_store(facility, level, lflags | LOG_CONT, 0, dict, dictlen, text, text_len);
+		}
+		/* Otherwise, make sure it's flushed */
+		cont_flush();
 	}
 
-	/*
-	 * If an earlier newline was missing and it was the same task,
-	 * either merge it with the current buffer and flush, or if
-	 * there was a race with interrupts (prefix == true) then just
-	 * flush it out and store this line separately.
-	 * If the preceding printk was from a different task and missed
-	 * a newline, flush and append the newline.
-	 */
-	if (cont.len) {
-		bool stored = false;
-
-		if (cont.owner == current && (lflags & LOG_CONT))
-			stored = cont_add(facility, level, text, text_len);
-		cont_flush(LOG_NEWLINE);
-		if (stored)
+	/* If it doesn't end in a newline, try to buffer the current line */
+	if (!(lflags & LOG_NEWLINE)) {
+		if (cont_add(facility, level, lflags, text, text_len))
 			return text_len;
 	}
 
+	/* Store it in the record log */
 	return log_store(facility, level, lflags, 0, dict, dictlen, text, text_len);
 }