Merge branch 'printk-cleanups'

Merge my system logging cleanups, triggered by the broken '\n' patches.

The line continuation handling has been broken basically forever, and
the code to handle the system log records was both confusing and
dubious. And it would do entirely the wrong thing unless you always had
a terminating newline, partly because it couldn't actually see whether a
message was marked KERN_CONT or not (but partly because the LOG_CONT
handling in the recording code was rather confusing too).

This re-introduces a real semantically meaningful KERN_CONT, and fixes
the few places I noticed where it was missing. There are probably more
missing cases, since KERN_CONT hasn't actually had any semantic meaning
for at least four years (other than the checkpatch meaning of "no log
level necessary, this is a continuation line").

This also allows the combination of KERN_CONT and a log level. In that
case the log level will be ignored if the merging with a previous line
is successful, but if a new record is needed, that new record will now
get the right log level.

That also means that you can at least in theory combine KERN_CONT with
the "pr_info()" style helpers, although any use of pr_fmt() prefixing
would make that just result in a mess, of course (the prefix would end
up in the middle of a continuing line).

* printk-cleanups:
printk: make reading the kernel log flush pending lines
printk: re-organize log_output() to be more legible
printk: split out core logging code into helper function
printk: reinstate KERN_CONT for printing continuation lines

drivers/tty/vt/vt.c

···
 
 	pr_info("Console: switching ");
 	if (!deflt)
-		printk("consoles %d-%d ", first+1, last+1);
+		printk(KERN_CONT "consoles %d-%d ", first+1, last+1);
 	if (j >= 0) {
 		struct vc_data *vc = vc_cons[j].d;
 
-		printk("to %s %s %dx%d\n",
+		printk(KERN_CONT "to %s %s %dx%d\n",
 		       vc->vc_can_do_color ? "colour" : "mono",
 		       desc, vc->vc_cols, vc->vc_rows);
 
···
 			update_screen(vc);
 		}
 	} else
-		printk("to %s\n", desc);
+		printk(KERN_CONT "to %s\n", desc);
 
 	retval = 0;
 err:

include/linux/kern_levels.h

···
  * 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	KERN_SOH "c"
 
 /* integer equivalents of KERN_<LEVEL> */
 #define LOGLEVEL_SCHED		-2	/* Deferred messages from sched code

include/linux/printk.h

···
 		switch (buffer[1]) {
 		case '0' ... '7':
 		case 'd':	/* KERN_DEFAULT */
+		case 'c':	/* KERN_CONT */
 			return buffer[1];
 		}
 	}

kernel/printk/printk.c

···
 	 * better readable output. 'c' in the record flags mark the first
 	 * fragment of a line, '+' the following.
 	 */
-	if (msg->flags & LOG_CONT && !(prev_flags & LOG_CONT))
-		cont = 'c';
-	else if ((msg->flags & LOG_CONT) ||
-		 ((prev_flags & LOG_CONT) && !(msg->flags & LOG_PREFIX)))
-		cont = '+';
+	if (msg->flags & LOG_CONT)
+		cont = (prev_flags & LOG_CONT) ? '+' : 'c';
 
 	return scnprintf(buf, size, "%u,%llu,%llu,%c;",
 		       (msg->facility << 3) | msg->level, seq, ts_usec, cont);
···
 	return ret;
 }
 
+static void cont_flush(void);
+
 static ssize_t devkmsg_read(struct file *file, char __user *buf,
 			    size_t count, loff_t *ppos)
 {
···
 	if (ret)
 		return ret;
 	raw_spin_lock_irq(&logbuf_lock);
+	cont_flush();
 	while (user->seq == log_next_seq) {
 		if (file->f_flags & O_NONBLOCK) {
 			ret = -EAGAIN;
···
 		return -ESPIPE;
 
 	raw_spin_lock_irq(&logbuf_lock);
+	cont_flush();
 	switch (whence) {
 	case SEEK_SET:
 		/* the first record */
···
 	poll_wait(file, &log_wait, wait);
 
 	raw_spin_lock_irq(&logbuf_lock);
+	cont_flush();
 	if (user->seq < log_next_seq) {
 		/* return error when data has vanished underneath us */
 		if (user->seq < log_first_seq)
···
 		size_t skip;
 
 		raw_spin_lock_irq(&logbuf_lock);
+		cont_flush();
 		if (syslog_seq < log_first_seq) {
 			/* messages are gone, move to first one */
 			syslog_seq = log_first_seq;
···
 		return -ENOMEM;
 
 	raw_spin_lock_irq(&logbuf_lock);
+	cont_flush();
 	if (buf) {
 		u64 next_seq;
 		u64 seq;
···
 	/* Number of chars in the log buffer */
 	case SYSLOG_ACTION_SIZE_UNREAD:
 		raw_spin_lock_irq(&logbuf_lock);
+		cont_flush();
 		if (syslog_seq < log_first_seq) {
 			/* messages are gone, move to first one */
 			syslog_seq = log_first_seq;
···
 	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;
···
 	 * 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;
 	}
 
···
 		cont.level = level;
 		cont.owner = current;
 		cont.ts_nsec = local_clock();
-		cont.flags = 0;
+		cont.flags = flags;
 		cont.cons = 0;
 		cont.flushed = false;
 	}
···
 	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;
 }
···
 		cont.len = 0;
 	}
 	return textlen;
+}
+
+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 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) {
+		if (cont.owner == current && (lflags & LOG_CONT)) {
+			if (cont_add(facility, level, lflags, text, text_len))
+				return text_len;
+		}
+		/* Otherwise, make sure it's flushed */
+		cont_flush();
+	}
+
+	/* 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);
 }
 
 asmlinkage int vprintk_emit(int facility, int level,
···
 
 	/* strip kernel syslog prefix and extract log level or control flags */
 	if (facility == 0) {
-		int kern_level = printk_get_level(text);
+		int kern_level;
 
-		if (kern_level) {
-			const char *end_of_header = printk_skip_level(text);
+		while ((kern_level = printk_get_level(text)) != 0) {
 			switch (kern_level) {
 			case '0' ... '7':
 				if (level == LOGLEVEL_DEFAULT)
···
 				/* fallthrough */
 			case 'd':	/* KERN_DEFAULT */
 				lflags |= LOG_PREFIX;
+				break;
+			case 'c':	/* KERN_CONT */
+				lflags |= LOG_CONT;
 			}
-			/*
-			 * No need to check length here because vscnprintf
-			 * put '\0' at the end of the string. Only valid and
-			 * newly printed level is detected.
-			 */
-			text_len -= end_of_header - text;
-			text = (char *)end_of_header;
+
+			text_len -= 2;
+			text += 2;
 		}
 	}
 
···
 	if (dict)
 		lflags |= LOG_PREFIX|LOG_NEWLINE;
 
-	if (!(lflags & LOG_NEWLINE)) {
-		/*
-		 * Flush the conflicting buffer. An earlier newline was missing,
-		 * or another task also prints continuation lines.
-		 */
-		if (cont.len && (lflags & LOG_PREFIX || cont.owner != current))
-			cont_flush(LOG_NEWLINE);
-
-		/* buffer line if possible, otherwise store it right away */
-		if (cont_add(facility, level, text, text_len))
-			printed_len += text_len;
-		else
-			printed_len += log_store(facility, level,
-						 lflags | LOG_CONT, 0,
-						 dict, dictlen, text, text_len);
-	} else {
-		bool stored = false;
-
-		/*
-		 * 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) {
-			if (cont.owner == current && !(lflags & LOG_PREFIX))
-				stored = cont_add(facility, level, text,
-						  text_len);
-			cont_flush(LOG_NEWLINE);
-		}
-
-		if (stored)
-			printed_len += text_len;
-		else
-			printed_len += log_store(facility, level, lflags, 0,
-						 dict, dictlen, text, text_len);
-	}
+	printed_len += log_output(facility, level, lflags, dict, dictlen, text, text_len);
 
 	logbuf_cpu = UINT_MAX;
 	raw_spin_unlock(&logbuf_lock);
···
 		dumper->active = true;
 
 		raw_spin_lock_irqsave(&logbuf_lock, flags);
+		cont_flush();
 		dumper->cur_seq = clear_seq;
 		dumper->cur_idx = clear_idx;
 		dumper->next_seq = log_next_seq;
···
 	bool ret;
 
 	raw_spin_lock_irqsave(&logbuf_lock, flags);
+	cont_flush();
 	ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
 	raw_spin_unlock_irqrestore(&logbuf_lock, flags);
 
···
 		goto out;
 
 	raw_spin_lock_irqsave(&logbuf_lock, flags);
+	cont_flush();
 	if (dumper->cur_seq < log_first_seq) {
 		/* messages are gone, move to first available one */
 		dumper->cur_seq = log_first_seq;

security/selinux/ss/policydb.c

···
 	printk(KERN_DEBUG "SELinux:  %d users, %d roles, %d types, %d bools",
 	       p->p_users.nprim, p->p_roles.nprim, p->p_types.nprim, p->p_bools.nprim);
 	if (p->mls_enabled)
-		printk(", %d sens, %d cats", p->p_levels.nprim,
+		printk(KERN_CONT ", %d sens, %d cats", p->p_levels.nprim,
 		       p->p_cats.nprim);
-	printk("\n");
+	printk(KERN_CONT "\n");
 
 	printk(KERN_DEBUG "SELinux:  %d classes, %d rules\n",
 	       p->p_classes.nprim, p->te_avtab.nel);