printk/btrfs: handle more message headers

Commit 4bcc595ccd ("printk: reinstate KERN_CONT for printing
continuation lines") allows to define more message headers for a single
message.  The motivation is that continuous lines might get mixed.
Therefore it make sense to define the right log level for every piece of
a cont line.

The current btrfs_printk() macros do not support continuous lines at the
moment.  But better be prepared for a custom messages and avoid
potential "lvl" buffer overflow.

This patch iterates over the entire message header.  It is interested
only into the message level like the original code.

This patch also introduces PRINTK_MAX_SINGLE_HEADER_LEN.  Three bytes
are enough for the message level header at the moment.  But it used to
be three, see the commit 04d2c8c83d ("printk: convert the format for
KERN_<LEVEL> to a 2 byte pattern").

Also I fixed the default ratelimit level.  It looked very strange when it
was different from the default log level.

[pmladek@suse.com: Fix a check of the valid message level]
  Link: http://lkml.kernel.org/r/20161111183236.GD2145@dhcp128.suse.cz
Link: http://lkml.kernel.org/r/1478695291-12169-4-git-send-email-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: David Sterba <dsterba@suse.com>
Cc: Joe Perches <joe@perches.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <jbacik@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/btrfs/super.c

@@ -202,27 +202,31 @@ static struct ratelimit_state printk_limits[] = {
 void btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...)
 {
 	struct super_block *sb = fs_info->sb;
-	char lvl[4];
+	char lvl[PRINTK_MAX_SINGLE_HEADER_LEN + 1];
 	struct va_format vaf;
 	va_list args;
-	const char *type = logtypes[4];
+	const char *type = NULL;
 	int kern_level;
 	struct ratelimit_state *ratelimit;
 
 	va_start(args, fmt);
 
-	kern_level = printk_get_level(fmt);
-	if (kern_level) {
+	while ((kern_level = printk_get_level(fmt)) != 0) {
 		size_t size = printk_skip_level(fmt) - fmt;
-		memcpy(lvl, fmt,  size);
-		lvl[size] = '\0';
+
+		if (kern_level >= '0' && kern_level <= '7') {
+			memcpy(lvl, fmt,  size);
+			lvl[size] = '\0';
+			type = logtypes[kern_level - '0'];
+			ratelimit = &printk_limits[kern_level - '0'];
+		}
 		fmt += size;
-		type = logtypes[kern_level - '0'];
-		ratelimit = &printk_limits[kern_level - '0'];
-	} else {
+	}
+
+	if (!type) {
 		*lvl = '\0';
-		/* Default to debug output */
-		ratelimit = &printk_limits[7];
+		type = logtypes[4];
+		ratelimit = &printk_limits[4];
 	}
 
 	vaf.fmt = fmt;

include/linux/printk.h

@@ -10,6 +10,8 @@
 extern const char linux_banner[];
 extern const char linux_proc_banner[];
 
+#define PRINTK_MAX_SINGLE_HEADER_LEN 2
+
 static inline int printk_get_level(const char *buffer)
 {
 	if (buffer[0] == KERN_SOH_ASCII && buffer[1]) {