seq_buf: Add seq_buf_terminate() API

In the case that the seq_buf buffer needs to be printed directly, add a way
to make sure that the buffer is safe to read by forcing a nul terminating
character at the end of the string, or the last byte of the buffer if the
string has overflowed.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

include/linux/seq_buf.h

@@ -71,6 +71,31 @@ static inline unsigned int seq_buf_used(struct seq_buf *s)
 	return min(s->len, s->size);
 }
 
+/**
+ * seq_buf_terminate - Make sure buffer is nul terminated
+ * @s: the seq_buf descriptor to terminate.
+ *
+ * This makes sure that the buffer in @s is nul terminated and
+ * safe to read as a string.
+ *
+ * Note, if this is called when the buffer has overflowed, then
+ * the last byte of the buffer is zeroed, and the len will still
+ * point passed it.
+ *
+ * After this function is called, s->buffer is safe to use
+ * in string operations.
+ */
+static inline void seq_buf_terminate(struct seq_buf *s)
+{
+	if (WARN_ON(s->size == 0))
+		return;
+
+	if (seq_buf_buffer_left(s))
+		s->buffer[s->len] = 0;
+	else
+		s->buffer[s->size - 1] = 0;
+}
+
 /**
  * seq_buf_get_buf - get buffer to write arbitrary data to
  * @s: the seq_buf handle