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Subject[PATCH 2/2] tracing/events: Show real number in array fields
From: Steven Rostedt <srostedt@redhat.com>

Currently we have in something like the sched_switch event:

field:char prev_comm[TASK_COMM_LEN]; offset:12; size:16; signed:1;

When a userspace tool such as perf tries to parse this, the
TASK_COMM_LEN is meaningless. This is done because the TRACE_EVENT() macro
simply uses a #len to show the string of the length. When the length is
an enum, we get a string that means nothing for tools.

By adding a static buffer and a mutex to protect it, we can store the
string into that buffer with snprintf and show the actual number.
Now we get:

field:char prev_comm[16]; offset:12; size:16; signed:1;

Something much more useful.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
include/linux/ftrace_event.h | 4 ++++
include/trace/ftrace.h | 14 ++++++++++----
kernel/trace/trace_events.c | 6 ++++++
kernel/trace/trace_export.c | 14 ++++++++++----
4 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 725bf6b..47e3997 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -225,6 +225,10 @@ enum {
FILTER_PTR_STRING,
};

+#define EVENT_STORAGE_SIZE 128
+extern struct mutex event_storage_mutex;
+extern char event_storage[EVENT_STORAGE_SIZE];
+
extern int trace_event_raw_init(struct ftrace_event_call *call);
extern int trace_define_field(struct ftrace_event_call *call, const char *type,
const char *name, int offset, int size,
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index e718a91..e16610c 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -296,13 +296,19 @@ static struct trace_event_functions ftrace_event_type_funcs_##call = { \

#undef __array
#define __array(type, item, len) \
- BUILD_BUG_ON(len > MAX_FILTER_STR_VAL); \
- ret = trace_define_field(event_call, #type "[" #len "]", #item, \
+ do { \
+ mutex_lock(&event_storage_mutex); \
+ BUILD_BUG_ON(len > MAX_FILTER_STR_VAL); \
+ snprintf(event_storage, sizeof(event_storage), \
+ "%s[%d]", #type, len); \
+ ret = trace_define_field(event_call, event_storage, #item, \
offsetof(typeof(field), item), \
sizeof(field.item), \
is_signed_type(type), FILTER_OTHER); \
- if (ret) \
- return ret;
+ mutex_unlock(&event_storage_mutex); \
+ if (ret) \
+ return ret; \
+ } while (0);

#undef __dynamic_array
#define __dynamic_array(type, item, len) \
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 0725eea..35fde09 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -27,6 +27,12 @@

DEFINE_MUTEX(event_mutex);

+DEFINE_MUTEX(event_storage_mutex);
+EXPORT_SYMBOL_GPL(event_storage_mutex);
+
+char event_storage[EVENT_STORAGE_SIZE];
+EXPORT_SYMBOL_GPL(event_storage);
+
LIST_HEAD(ftrace_events);
LIST_HEAD(ftrace_common_fields);

diff --git a/kernel/trace/trace_export.c b/kernel/trace/trace_export.c
index 4ba44de..4b74d71 100644
--- a/kernel/trace/trace_export.c
+++ b/kernel/trace/trace_export.c
@@ -83,13 +83,19 @@ static void __always_unused ____ftrace_check_##name(void) \

#undef __array
#define __array(type, item, len) \
- BUILD_BUG_ON(len > MAX_FILTER_STR_VAL); \
- ret = trace_define_field(event_call, #type "[" #len "]", #item, \
+ do { \
+ BUILD_BUG_ON(len > MAX_FILTER_STR_VAL); \
+ mutex_lock(&event_storage_mutex); \
+ snprintf(event_storage, sizeof(event_storage), \
+ "%s[%d]", #type, len); \
+ ret = trace_define_field(event_call, event_storage, #item, \
offsetof(typeof(field), item), \
sizeof(field.item), \
is_signed_type(type), FILTER_OTHER); \
- if (ret) \
- return ret;
+ mutex_unlock(&event_storage_mutex); \
+ if (ret) \
+ return ret; \
+ } while (0);

#undef __array_desc
#define __array_desc(type, container, item, len) \
--
1.7.1



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