[RFC PATCH] ftrace trace event: introduce assignment macros

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

This patch proposes encapsulation of the raw assignments within TP_fast_assign()
by introducing tp_assign() and tp_memcpy() macros. This will allow us to:

- generically filter from input fields,
- redefine the field write primitives.

The current macros map directly to the old code. I changed the documentation in
tracepoint.txt to reflect these new primitives, but all TRACE_EVENT() users
should gradually update their code to use these macro wrappers rather than raw
"=" assignments or mempcy() calls.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Ingo Molnar <mingo@redhat.com>
CC: Li Zefan <lizf@cn.fujitsu.com>
CC: William Cohen <wcohen@redhat.com>
CC: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
CC: Theodore Ts'o <tytso@mit.edu>
CC: Jason Baron <jbaron@redhat.com>
CC: Mel Gorman <mel@csn.ul.ie>
CC: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
CC: Marcelo Tosatti <mtosatti@redhat.com>
CC: Avi Kivity <avi@redhat.com>
CC: Gleb Natapov <gleb@redhat.com>
CC: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
CC: Neil Horman <nhorman@tuxdriver.com>
CC: Arjan van de Ven <arjan@linux.intel.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Kei Tokunaga <tokunaga.keiich@jp.fujitsu.com>
CC: Martin K. Petersen <martin.petersen@oracle.com>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Masami Hiramatsu <mhiramat@redhat.com>
CC: Josh Stone <jistone@redhat.com>
CC: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Zhaolei <zhaolei@cn.fujitsu.com>
CC: Anton Blanchard <anton@samba.org>
---
 include/linux/tracepoint.h |   12 ++++++------
 include/trace/ftrace.h     |    6 ++++++
 2 files changed, 12 insertions(+), 6 deletions(-)

Index: linux-2.6-lttng.git/include/trace/ftrace.h
===================================================================
--- linux-2.6-lttng.git.orig/include/trace/ftrace.h
+++ linux-2.6-lttng.git/include/trace/ftrace.h
@@ -1,4 +1,10 @@
 /*
+ * Macros mapping tp_assign() and tp_memcpy() to "=" and memcpy.
+ */
+#define tp_assign(dest, src)		__entry->dest = src
+#define tp_memcpy(dest, src, len)	memcpy(__entry->dest, src, len)
+
+/*
  * Stage 1 of the trace events.
  *
  * Override the macros in <trace/trace_events.h> to include the following:
Index: linux-2.6-lttng.git/include/linux/tracepoint.h
===================================================================
--- linux-2.6-lttng.git.orig/include/linux/tracepoint.h
+++ linux-2.6-lttng.git/include/linux/tracepoint.h
@@ -306,12 +306,12 @@ static inline void tracepoint_update_pro
  *	*
  *
  *	TP_fast_assign(
- *		memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN);
- *		__entry->prev_pid	= prev->pid;
- *		__entry->prev_prio	= prev->prio;
- *		memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN);
- *		__entry->next_pid	= next->pid;
- *		__entry->next_prio	= next->prio;
+ *		tp_memcpy(next_comm, next->comm, TASK_COMM_LEN);
+ *		tp_assign(prev_pid, prev->pid);
+ *		tp_assign(prev_prio, prev->prio);
+ *		tp_memcpy(prev_comm, prev->comm, TASK_COMM_LEN);
+ *		tp_assign(next_pid, next->pid);
+ *		tp_assign(next_prio, next->prio);
  *	)
  *
  *	*

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com