kmsg-merge-cont.patch

From: Kay Sievers <kay@vrfy.org>
Subject: kmsg: merge continuation records while printing

In (the unlikely) case our continuation merge buffer is busy, we unfortunately
can not merge further continuation printk()s into a single record and have to
store them separately, which leads to split-up output of these lines when they
are printed.

Add some flags about newlines and prefix existence to these records and try to
reconstruct the full line again, when the separated records are printed.

Reported-By: Michael Neuling <mikey@neuling.org>
Tested-By: Michael Neuling <mikey@neuling.org>
Signed-off-by: Kay Sievers <kay@vrfy.org>
---
 kernel/printk.c |  120 ++++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 78 insertions(+), 42 deletions(-)

--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -194,8 +194,10 @@ static int console_may_schedule;
  */
 
 enum log_flags {
-	LOG_DEFAULT = 0,
-	LOG_NOCONS = 1,		/* already flushed, do not print to console */
+	LOG_NOCONS	= 1,	/* already flushed, do not print to console */
+	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 */
 };
 
 struct log {
@@ -217,6 +219,7 @@ static DEFINE_RAW_SPINLOCK(logbuf_lock);
 /* the next printk record to read by syslog(READ) or /proc/kmsg */
 static u64 syslog_seq;
 static u32 syslog_idx;
+static enum log_flags syslog_prev;
 static size_t syslog_partial;
 
 /* index and sequence number of the first record stored in the buffer */
@@ -839,13 +842,26 @@ static size_t print_prefix(const struct
 	return len;
 }
 
-static size_t msg_print_text(const struct log *msg, bool syslog,
-			     char *buf, size_t size)
+static size_t msg_print_text(const struct log *msg, enum log_flags prev,
+			     bool syslog, char *buf, size_t size)
 {
 	const char *text = log_text(msg);
 	size_t text_size = msg->text_len;
+	bool prefix = true;
+	bool newline = true;
 	size_t len = 0;
 
+	if ((prev & LOG_CONT) && !(msg->flags & LOG_PREFIX))
+		prefix = false;
+
+	if (msg->flags & LOG_CONT) {
+		if ((prev & LOG_CONT) && !(prev & LOG_NEWLINE))
+			prefix = false;
+
+		if (!(msg->flags & LOG_NEWLINE))
+			newline = false;
+	}
+
 	do {
 		const char *next = memchr(text, '\n', text_size);
 		size_t text_len;
@@ -863,16 +879,22 @@ static size_t msg_print_text(const struc
 			    text_len + 1>= size - len)
 				break;
 
-			len += print_prefix(msg, syslog, buf + len);
+			if (prefix)
+				len += print_prefix(msg, syslog, buf + len);
 			memcpy(buf + len, text, text_len);
 			len += text_len;
-			buf[len++] = '\n';
+			if (next || newline)
+				buf[len++] = '\n';
 		} else {
 			/* SYSLOG_ACTION_* buffer size only calculation */
-			len += print_prefix(msg, syslog, NULL);
-			len += text_len + 1;
+			if (prefix)
+				len += print_prefix(msg, syslog, NULL);
+			len += text_len;
+			if (next || newline)
+				len++;
 		}
 
+		prefix = true;
 		text = next;
 	} while (text);
 
@@ -898,6 +920,7 @@ static int syslog_print(char __user *buf
 			/* messages are gone, move to first one */
 			syslog_seq = log_first_seq;
 			syslog_idx = log_first_idx;
+			syslog_prev = 0;
 			syslog_partial = 0;
 		}
 		if (syslog_seq == log_next_seq) {
@@ -907,11 +930,12 @@ static int syslog_print(char __user *buf
 
 		skip = syslog_partial;
 		msg = log_from_idx(syslog_idx);
-		n = msg_print_text(msg, true, text, LOG_LINE_MAX);
+		n = msg_print_text(msg, syslog_prev, true, text, LOG_LINE_MAX);
 		if (n - syslog_partial <= size) {
 			/* message fits into buffer, move forward */
 			syslog_idx = log_next(syslog_idx);
 			syslog_seq++;
+			syslog_prev = msg->flags;
 			n -= syslog_partial;
 			syslog_partial = 0;
 		} else if (!len){
@@ -954,6 +978,7 @@ static int syslog_print_all(char __user
 		u64 next_seq;
 		u64 seq;
 		u32 idx;
+		enum log_flags prev;
 
 		if (clear_seq < log_first_seq) {
 			/* messages are gone, move to first available one */
@@ -967,10 +992,11 @@ static int syslog_print_all(char __user
 		 */
 		seq = clear_seq;
 		idx = clear_idx;
+		prev = 0;
 		while (seq < log_next_seq) {
 			struct log *msg = log_from_idx(idx);
 
-			len += msg_print_text(msg, true, NULL, 0);
+			len += msg_print_text(msg, prev, true, NULL, 0);
 			idx = log_next(idx);
 			seq++;
 		}
@@ -978,10 +1004,11 @@ static int syslog_print_all(char __user
 		/* move first record forward until length fits into the buffer */
 		seq = clear_seq;
 		idx = clear_idx;
+		prev = 0;
 		while (len > size && seq < log_next_seq) {
 			struct log *msg = log_from_idx(idx);
 
-			len -= msg_print_text(msg, true, NULL, 0);
+			len -= msg_print_text(msg, prev, true, NULL, 0);
 			idx = log_next(idx);
 			seq++;
 		}
@@ -990,17 +1017,19 @@ static int syslog_print_all(char __user
 		next_seq = log_next_seq;
 
 		len = 0;
+		prev = 0;
 		while (len >= 0 && seq < next_seq) {
 			struct log *msg = log_from_idx(idx);
 			int textlen;
 
-			textlen = msg_print_text(msg, true, text, LOG_LINE_MAX);
+			textlen = msg_print_text(msg, prev, true, text, LOG_LINE_MAX);
 			if (textlen < 0) {
 				len = textlen;
 				break;
 			}
 			idx = log_next(idx);
 			seq++;
+			prev = msg->flags;
 
 			raw_spin_unlock_irq(&logbuf_lock);
 			if (copy_to_user(buf + len, text, textlen))
@@ -1013,6 +1042,7 @@ static int syslog_print_all(char __user
 				/* messages are gone, move to next one */
 				seq = log_first_seq;
 				idx = log_first_idx;
+				prev = 0;
 			}
 		}
 	}
@@ -1117,6 +1147,7 @@ int do_syslog(int type, char __user *buf
 			/* messages are gone, move to first one */
 			syslog_seq = log_first_seq;
 			syslog_idx = log_first_idx;
+			syslog_prev = 0;
 			syslog_partial = 0;
 		}
 		if (from_file) {
@@ -1127,18 +1158,18 @@ int do_syslog(int type, char __user *buf
 			 */
 			error = log_next_idx - syslog_idx;
 		} else {
-			u64 seq;
-			u32 idx;
+			u64 seq = syslog_seq;
+			u32 idx = syslog_idx;
+			enum log_flags prev = syslog_prev;
 
 			error = 0;
-			seq = syslog_seq;
-			idx = syslog_idx;
 			while (seq < log_next_seq) {
 				struct log *msg = log_from_idx(idx);
 
-				error += msg_print_text(msg, true, NULL, 0);
+				error += msg_print_text(msg, prev, true, NULL, 0);
 				idx = log_next(idx);
 				seq++;
+				prev = msg->flags;
 			}
 			error -= syslog_partial;
 		}
@@ -1408,10 +1439,9 @@ asmlinkage int vprintk_emit(int facility
 	static char textbuf[LOG_LINE_MAX];
 	char *text = textbuf;
 	size_t text_len;
+	enum log_flags lflags = 0;
 	unsigned long flags;
 	int this_cpu;
-	bool newline = false;
-	bool prefix = false;
 	int printed_len = 0;
 
 	boot_delay_msec();
@@ -1450,7 +1480,7 @@ asmlinkage int vprintk_emit(int facility
 		recursion_bug = 0;
 		printed_len += strlen(recursion_msg);
 		/* emit KERN_CRIT message */
-		log_store(0, 2, LOG_DEFAULT, 0,
+		log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0,
 			  NULL, 0, recursion_msg, printed_len);
 	}
 
@@ -1463,7 +1493,7 @@ asmlinkage int vprintk_emit(int facility
 	/* mark and strip a trailing newline */
 	if (text_len && text[text_len-1] == '\n') {
 		text_len--;
-		newline = true;
+		lflags |= LOG_NEWLINE;
 	}
 
 	/* strip syslog prefix and extract log level or control flags */
@@ -1473,7 +1503,7 @@ asmlinkage int vprintk_emit(int facility
 			if (level == -1)
 				level = text[1] - '0';
 		case 'd':	/* KERN_DEFAULT */
-			prefix = true;
+			lflags |= LOG_PREFIX;
 		case 'c':	/* KERN_CONT */
 			text += 3;
 			text_len -= 3;
@@ -1483,22 +1513,20 @@ asmlinkage int vprintk_emit(int facility
 	if (level == -1)
 		level = default_message_loglevel;
 
-	if (dict) {
-		prefix = true;
-		newline = true;
-	}
+	if (dict)
+		lflags |= LOG_PREFIX|LOG_NEWLINE;
 
-	if (!newline) {
+	if (!(lflags & LOG_NEWLINE)) {
 		/*
 		 * Flush the conflicting buffer. An earlier newline was missing,
 		 * or another task also prints continuation lines.
 		 */
-		if (cont.len && (prefix || cont.owner != current))
+		if (cont.len && (lflags & LOG_PREFIX || cont.owner != current))
 			cont_flush();
 
 		/* buffer line if possible, otherwise store it right away */
 		if (!cont_add(facility, level, text, text_len))
-			log_store(facility, level, LOG_DEFAULT, 0,
+			log_store(facility, level, lflags | LOG_CONT, 0,
 				  dict, dictlen, text, text_len);
 	} else {
 		bool stored = false;
@@ -1510,13 +1538,13 @@ asmlinkage int vprintk_emit(int facility
 		 * flush it out and store this line separately.
 		 */
 		if (cont.len && cont.owner == current) {
-			if (!prefix)
+			if (!(lflags & LOG_PREFIX))
 				stored = cont_add(facility, level, text, text_len);
 			cont_flush();
 		}
 
 		if (!stored)
-			log_store(facility, level, LOG_DEFAULT, 0,
+			log_store(facility, level, lflags, 0,
 				  dict, dictlen, text, text_len);
 	}
 	printed_len += text_len;
@@ -1615,8 +1643,8 @@ static struct cont {
 static struct log *log_from_idx(u32 idx) { return NULL; }
 static u32 log_next(u32 idx) { return 0; }
 static void call_console_drivers(int level, const char *text, size_t len) {}
-static size_t msg_print_text(const struct log *msg, bool syslog,
-			     char *buf, size_t size) { return 0; }
+static size_t msg_print_text(const struct log *msg, enum log_flags prev,
+			     bool syslog, char *buf, size_t size) { return 0; }
 static size_t cont_print_text(char *text, size_t size) { return 0; }
 
 #endif /* CONFIG_PRINTK */
@@ -1892,6 +1920,7 @@ void wake_up_klogd(void)
 /* the next printk record to write to the console */
 static u64 console_seq;
 static u32 console_idx;
+static enum log_flags console_prev;
 
 /**
  * console_unlock - unlock the console system
@@ -1952,6 +1981,7 @@ again:
 			/* messages are gone, move to first one */
 			console_seq = log_first_seq;
 			console_idx = log_first_idx;
+			console_prev = 0;
 		}
 skip:
 		if (console_seq == log_next_seq)
@@ -1975,10 +2005,11 @@ skip:
 		}
 
 		level = msg->level;
-		len = msg_print_text(msg, false, text, sizeof(text));
-
+		len = msg_print_text(msg, console_prev, false,
+				     text, sizeof(text));
 		console_idx = log_next(console_idx);
 		console_seq++;
+		console_prev = msg->flags;
 		raw_spin_unlock(&logbuf_lock);
 
 		stop_critical_timings();	/* don't trace print latency */
@@ -2241,6 +2272,7 @@ void register_console(struct console *ne
 		raw_spin_lock_irqsave(&logbuf_lock, flags);
 		console_seq = syslog_seq;
 		console_idx = syslog_idx;
+		console_prev = syslog_prev;
 		raw_spin_unlock_irqrestore(&logbuf_lock, flags);
 		/*
 		 * We're about to replay the log buffer.  Only do this to the
@@ -2534,8 +2566,7 @@ bool kmsg_dump_get_line(struct kmsg_dump
 	}
 
 	msg = log_from_idx(dumper->cur_idx);
-	l = msg_print_text(msg, syslog,
-			      line, size);
+	l = msg_print_text(msg, 0, syslog, line, size);
 
 	dumper->cur_idx = log_next(dumper->cur_idx);
 	dumper->cur_seq++;
@@ -2575,6 +2606,7 @@ bool kmsg_dump_get_buffer(struct kmsg_du
 	u32 idx;
 	u64 next_seq;
 	u32 next_idx;
+	enum log_flags prev;
 	size_t l = 0;
 	bool ret = false;
 
@@ -2597,23 +2629,27 @@ bool kmsg_dump_get_buffer(struct kmsg_du
 	/* calculate length of entire buffer */
 	seq = dumper->cur_seq;
 	idx = dumper->cur_idx;
+	prev = 0;
 	while (seq < dumper->next_seq) {
 		struct log *msg = log_from_idx(idx);
 
-		l += msg_print_text(msg, true, NULL, 0);
+		l += msg_print_text(msg, prev, true, NULL, 0);
 		idx = log_next(idx);
 		seq++;
+		prev = msg->flags;
 	}
 
 	/* move first record forward until length fits into the buffer */
 	seq = dumper->cur_seq;
 	idx = dumper->cur_idx;
+	prev = 0;
 	while (l > size && seq < dumper->next_seq) {
 		struct log *msg = log_from_idx(idx);
 
-		l -= msg_print_text(msg, true, NULL, 0);
+		l -= msg_print_text(msg, prev, true, NULL, 0);
 		idx = log_next(idx);
 		seq++;
+		prev = msg->flags;
 	}
 
 	/* last message in next interation */
@@ -2621,14 +2657,14 @@ bool kmsg_dump_get_buffer(struct kmsg_du
 	next_idx = idx;
 
 	l = 0;
+	prev = 0;
 	while (seq < dumper->next_seq) {
 		struct log *msg = log_from_idx(idx);
 
-		l += msg_print_text(msg, syslog,
-				    buf + l, size - l);
-
+		l += msg_print_text(msg, prev, syslog, buf + l, size - l);
 		idx = log_next(idx);
 		seq++;
+		prev = msg->flags;
 	}
 
 	dumper->next_seq = next_seq;