[PATCH v5 2/7] printk: insert newline for truncated records

[Alex Elder]

If a log record has LOG_PREFIX set, its predecessor record should be
terminated if it was marked LOG_CONT.

In devkmsg_read(), this condition was being ignored, which would
lead to such records showing up combined when reading /dev/kmsg.
Fix this oversight.

We should similarly insert a newline in msg_print_text() in this
case, to avoid formatted records getting merged.

Suggested-by: Petr MlÃdek <pmladek@xxxxxxx>
Signed-off-by: Alex Elder <elder@xxxxxxxxxx>
---
 kernel/printk/printk.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ffc9928..9f11eab 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -575,6 +575,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 	char cont = '-';
 	size_t len;
 	ssize_t ret;
+	bool insert_newline;
 
 	if (!user)
 		return -EBADF;
@@ -625,7 +626,10 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 		 ((user->prev & LOG_CONT) && !(msg->flags & LOG_PREFIX)))
 		cont = '+';
 
-	len = sprintf(user->buf, "%u,%llu,%llu,%c;",
+	/* Insert a newline if the previous line was not terminated properly */
+	insert_newline = (user->prev & LOG_CONT) && (msg->flags & LOG_PREFIX);
+	len = sprintf(user->buf, "%s%u,%llu,%llu,%c;",
+		      insert_newline ? "\n" : "",
 		      (msg->facility << 3) | msg->level,
 		      user->seq, ts_usec, cont);
 	user->prev = msg->flags;
@@ -1013,6 +1017,12 @@ static size_t msg_print_text(const struct printk_log *msg, enum log_flags prev,
 			newline = false;
 	}
 
+	if ((prev & LOG_CONT) && (msg->flags & LOG_PREFIX) && len < size) {
+		if (buf)
+			buf[len++] = '\n';
+		else
+			len++;
+	}
 	do {
 		const char *next = memchr(text, '\n', text_size);
 		size_t text_len;
-- 
1.9.1

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