tracing: Create new TRACE_EVENT_TEMPLATE

There are some places in the kernel that define several tracepoints and
they are all identical besides the name. The code to enable, disable and
record is created for every trace point even if most of the code is
identical.

This patch adds TRACE_EVENT_TEMPLATE that lets the developer create
a template TRACE_EVENT and create trace points with DEFINE_EVENT, which
is based off of a given template. Each trace point used by this
will share most of the code, and bring down the size of the kernel
when there are several duplicate events.

Usage is:

TRACE_EVENT_TEMPLATE(name, proto, args, tstruct, assign, print);

Which would be the same as defining a normal TRACE_EVENT.

To create the trace events that the trace points will use:

DEFINE_EVENT(template, name, proto, args) is done. The template
is the name of the TRACE_EVENT_TEMPLATE to use. The name is the
name of the trace point. The parameters proto and args must be the same
as the proto and args of the template. If they are not the same,
then a compile error will result. I tried hard removing this duplication
but the C preprocessor is not powerful enough (or my CPP magic
experience points is not at a high enough level) to not need them.

A lot of trace events are coming in with new XFS development. Most of
the trace points are identical except for the name. The following shows
the advantage of having TRACE_EVENT_TEMPLATE:

$ size fs/xfs/xfs.o.*
    text          data     bss     dec     hex filename
  452114          2788    3520  458422   6feb6 fs/xfs/xfs.o.old
  638482         38116    3744  680342   a6196 fs/xfs/xfs.o.template
  996954         38116    4480 1039550   fdcbe fs/xfs/xfs.o.trace

xfs.o.old is without any tracepoints.
xfs.o.template uses the new TRACE_EVENT_TEMPLATE.
xfs.o.trace uses the current TRACE_EVENT macros.

Requested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 2aac8a83e89b..88a5b5a809ec 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -280,6 +280,10 @@ static inline void tracepoint_synchronize_unregister(void)
  * TRACE_EVENT_FN to perform any (un)registration work.
  */
 
+#define TRACE_EVENT_TEMPLATE(name, proto, args, tstruct, assign, print)
+#define DEFINE_EVENT(template, name, proto, args)               \
+        DECLARE_TRACE(name, PARAMS(proto), PARAMS(args))
+
 #define TRACE_EVENT(name, proto, args, struct, assign, print)   \
         DECLARE_TRACE(name, PARAMS(proto), PARAMS(args))
 #define TRACE_EVENT_FN(name, proto, args, struct,               \