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SubjectRe: [PATCH] Fix tracing infrastructure to support multiple includes when defining CREATE_TRACE_POINTS
On Thu, Dec 03, 2009 at 09:15:26AM -0500, Steven Rostedt wrote:
> On Wed, 2009-12-02 at 14:19 -0500, Neil Horman wrote:
> > Fix tracing infrastructure to allow multiple header files with TRACE_EVENTS to
> > be included with CREATE_TRACE_EVENTS defined
> >
> > I've been workingon adding a few tracepoints to the network stack, and in so
> > doing it was convienient for me to add a second include file to
> > net/core/net-traces.c with TRACE_EVENTS defined in them. net-traces.c defines
> > CREATE_TRACE_EVENTS, and during the build it was failing, complaining about
> > duplicate definitions of __tpstrtab_<name>. I tracked down the bug to find that
> > define_trace.h redefined DECLARE_TRACE to be DEFINE_TRACE, so after the first
> > run through define_trace.h (which is included from skb.h, included in
> > net-trace.c first), the DECLARE_TRACE macro was left with an improper definition
> > to start a new cycle with the next header.
> >
> > The fix I came up with was to make sure that DECLARE_TRACE was undefined at the
> > end of define_trace.h, and to add a conditional re-definition in tracepoint.h.
> > This places us back in the proper state to define a new set of tracepoints in a
> > subsequent header file. Not sure if theres a better way to handle this, but
> > this worked well for me, allowing me to include multiple headers with
> > TRACE_EVENT macros in a c file with CREATE_TRACE_POINTS defined.
> >
>
> Nice, just some comments below.
><snip>
>
> You duplicate the DECLARE_TRACE from above and place it into an
> unprotected area. Why not move it instead of duplicating it. This is
> just a bug waiting to happen if we ever need to modify DECLARE_TRACE.
>
> If you change it to:
>
> #if !defined(CONFIG_TRACEPOINTS) && !defined(DECLARE_TRACE)
>
> #define DECLARE_TRACE(...) ....
>
> #endif
>
> Then you can remove the first definition of it. The first time
> processing the file, when it hits the #ifndef DECLARE_TRACE in the
> _LINUX_TRACEPOINT_H conditional, it still does not define DECLARE_TRACE,
> and then when it exits that conditional, it does.


Yeah, that makes sense to me. Although I think you mean if
defined(CONFIG_TRACEPOINTS) rather than if !defined(CONFIG_TRACEPOINTS). The
case I'm moving to outside the unprotected area is the one that we use if
tracepoints are enabled. I just tested this new patch, and it works well for
me. Thanks!

Neil

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>


linux/tracepoint.h | 45 +++++++++++++++++++++++----------------------
trace/define_trace.h | 1 +
2 files changed, 24 insertions(+), 22 deletions(-)


Fix tracing infrastructure to allow multiple header files with TRACE_EVENTS to
be included with CREATE_TRACE_EVENTS defined

I've been workingon adding a few tracepoints to the network stack, and in so
doing it was convienient for me to add a second include file to
net/core/net-traces.c with TRACE_EVENTS defined in them. net-traces.c defines
CREATE_TRACE_EVENTS, and during the build it was failing, complaining about
duplicate definitions of __tpstrtab_<name>. I tracked down the bug to find that
define_trace.h redefined DECLARE_TRACE to be DEFINE_TRACE, so after the first
run through define_trace.h (which is included from skb.h, included in
net-trace.c first), the DECLARE_TRACE macro was left with an improper definition
to start a new cycle with the next header.

The fix I came up with was to make sure that DECLARE_TRACE was undefined at the
end of define_trace.h, and to add a conditional re-definition in tracepoint.h.
This places us back in the proper state to define a new set of tracepoints in a
subsequent header file.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 2aac8a8..311abbf 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -58,28 +58,6 @@ struct tracepoint {
rcu_read_unlock_sched_notrace(); \
} while (0)

-/*
- * Make sure the alignment of the structure in the __tracepoints section will
- * not add unwanted padding between the beginning of the section and the
- * structure. Force alignment to the same alignment as the section start.
- */
-#define DECLARE_TRACE(name, proto, args) \
- extern struct tracepoint __tracepoint_##name; \
- static inline void trace_##name(proto) \
- { \
- if (unlikely(__tracepoint_##name.state)) \
- __DO_TRACE(&__tracepoint_##name, \
- TP_PROTO(proto), TP_ARGS(args)); \
- } \
- static inline int register_trace_##name(void (*probe)(proto)) \
- { \
- return tracepoint_probe_register(#name, (void *)probe); \
- } \
- static inline int unregister_trace_##name(void (*probe)(proto)) \
- { \
- return tracepoint_probe_unregister(#name, (void *)probe);\
- }
-

#define DEFINE_TRACE_FN(name, reg, unreg) \
static const char __tpstrtab_##name[] \
@@ -173,6 +151,29 @@ static inline void tracepoint_synchronize_unregister(void)
* trace event headers under one "CREATE_TRACE_POINTS" the first include
* will override the TRACE_EVENT and break the second include.
*/
+#if defined(CONFIG_TRACEPOINTS) && !defined(DECLARE_TRACE)
+/*
+ * Make sure the alignment of the structure in the __tracepoints section will
+ * not add unwanted padding between the beginning of the section and the
+ * structure. Force alignment to the same alignment as the section start.
+ */
+#define DECLARE_TRACE(name, proto, args) \
+ extern struct tracepoint __tracepoint_##name; \
+ static inline void trace_##name(proto) \
+ { \
+ if (unlikely(__tracepoint_##name.state)) \
+ __DO_TRACE(&__tracepoint_##name, \
+ TP_PROTO(proto), TP_ARGS(args)); \
+ } \
+ static inline int register_trace_##name(void (*probe)(proto)) \
+ { \
+ return tracepoint_probe_register(#name, (void *)probe); \
+ } \
+ static inline int unregister_trace_##name(void (*probe)(proto)) \
+ { \
+ return tracepoint_probe_unregister(#name, (void *)probe);\
+ }
+#endif

#ifndef TRACE_EVENT
/*
diff --git a/include/trace/define_trace.h b/include/trace/define_trace.h
index 2a4b3bf..a3e0095 100644
--- a/include/trace/define_trace.h
+++ b/include/trace/define_trace.h
@@ -64,6 +64,7 @@
#undef TRACE_EVENT
#undef TRACE_EVENT_FN
#undef TRACE_HEADER_MULTI_READ
+#undef DECLARE_TRACE

/* Only undef what we defined in this file */
#ifdef UNDEF_TRACE_INCLUDE_FILE

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