tracing: Add trace_seq_has_overflowed() and trace_handle_return()

Adding a trace_seq_has_overflowed() which returns true if the trace_seq
had too much written into it allows us to simplify the code.

Instead of checking the return value of every call to trace_seq_printf()
and friends, they can all be called normally, and at the end we can
return !trace_seq_has_overflowed() instead.

Several functions also return TRACE_TYPE_PARTIAL_LINE when the trace_seq
overflowed and TRACE_TYPE_HANDLED otherwise. Another helper function
was created called trace_handle_return() which takes a trace_seq and
returns these enums. Using this helper function also simplifies the
code.

This change also makes it possible to remove the return values of
trace_seq_printf() and friends. They should instead just be
void functions.

Link: http://lkml.kernel.org/r/20141114011410.365183157@goodmis.org

Reviewed-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

include/linux/trace_seq.h

@@ -40,6 +40,18 @@ trace_seq_buffer_ptr(struct trace_seq *s)
 	return s->buffer + s->len;
 }
 
+/**
+ * trace_seq_has_overflowed - return true if the trace_seq took too much
+ * @s: trace sequence descriptor
+ *
+ * Returns true if too much data was added to the trace_seq and it is
+ * now full and will not take anymore.
+ */
+static inline bool trace_seq_has_overflowed(struct trace_seq *s)
+{
+	return s->full || s->len > PAGE_SIZE - 1;
+}
+
 /*
  * Currently only defined when tracing is enabled.
  */