tracing/filters: add run-time field descriptions to TRACE_EVENT_FORMAT events

This patch adds run-time field descriptions to all the event formats
exported using TRACE_EVENT_FORMAT.  It also hooks up all the tracers
that use them (i.e. the tracers in the 'ftrace subsystem') so they can
also have their output filtered by the event-filtering mechanism.

When I was testing this, there were a couple of things that fooled me
into thinking the filters weren't working, when actually they were -
I'll mention them here so others don't make the same mistakes (and file
bug reports. ;-)

One is that some of the tracers trace multiple events e.g. the
sched_switch tracer uses the context_switch and wakeup events, and if
you don't set filters on all of the traced events, the unfiltered output
from the events without filters on them can make it look like the
filtering as a whole isn't working properly, when actually it is doing
what it was asked to do - it just wasn't asked to do the right thing.

The other is that for the really high-volume tracers e.g. the function
tracer, the volume of filtered events can be so high that it pushes the
unfiltered events out of the ring buffer before they can be read so e.g.
cat'ing the trace file repeatedly shows either no output, or once in
awhile some output but that isn't there the next time you read the
trace, which isn't what you normally expect when reading the trace file.
If you read from the trace_pipe file though, you can catch them before
they disappear.

Changes from v1:

As suggested by Frederic Weisbecker:

- get rid of externs in functions
- added unlikely() to filter_check_discard()

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 20 insertions, 0 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 34b94c3f40a..e7737281953 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -866,6 +866,21 @@ extern void filter_free_subsystem_preds(struct event_subsystem *system);
 extern int filter_add_subsystem_pred(struct event_subsystem *system,
 				     struct filter_pred *pred);
 
+static inline void
+filter_check_discard(struct ftrace_event_call *call, void *rec,
+		     struct ring_buffer_event *event)
+{
+	if (unlikely(call->preds) && !filter_match_preds(call, rec))
+		ring_buffer_event_discard(event);
+}
+
+#define __common_field(type, item)					\
+	ret = trace_define_field(event_call, #type, "common_" #item,	\
+				 offsetof(typeof(field.ent), item),	\
+				 sizeof(field.ent.item));		\
+	if (ret)							\
+		return ret;
+
 void event_trace_printk(unsigned long ip, const char *fmt, ...);
 extern struct ftrace_event_call __start_ftrace_events[];
 extern struct ftrace_event_call __stop_ftrace_events[];
@@ -897,4 +912,9 @@ do {									\
 		__trace_printk(ip, fmt, ##args);			\
 } while (0)
 
+#undef TRACE_EVENT_FORMAT
+#define TRACE_EVENT_FORMAT(call, proto, args, fmt, tstruct, tpfmt)	\
+	extern struct ftrace_event_call event_##call;
+#include "trace_event_types.h"
+
 #endif /* _LINUX_KERNEL_TRACE_H */