tracing: Add __field_struct macro for TRACE_EVENT()

Currently the __field() macro in TRACE_EVENT is only good for primitive
values, such as integers and pointers, but it fails on complex data types
such as structures or unions. This is because the __field() macro
determines if the variable is signed or not with the test of:

  (((type)(-1)) < (type)1)

Unfortunately, that fails when type is a structure.

Since trace events should support structures as fields a new macro
is created for such a case called __field_struct() which acts exactly
the same as __field() does but it does not do the signed type check
and just uses a constant false for that answer.

Cc: Tony Luck <tony.luck@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 35 insertions, 1 deletions

diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 0fd06fef9fac..26b4f2e13275 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -44,6 +44,12 @@
 #undef __field_ext
 #define __field_ext(type, item, filter_type)    type    item;
 
+#undef __field_struct
+#define __field_struct(type, item)      type    item;
+
+#undef __field_struct_ext
+#define __field_struct_ext(type, item, filter_type)     type    item;
+
 #undef __array
 #define __array(type, item, len)        type    item[len];
 
@@ -122,6 +128,12 @@
 #undef __field_ext
 #define __field_ext(type, item, filter_type)
 
+#undef __field_struct
+#define __field_struct(type, item)
+
+#undef __field_struct_ext
+#define __field_struct_ext(type, item, filter_type)
+
 #undef __array
 #define __array(type, item, len)
 
@@ -315,9 +327,21 @@ static struct trace_event_functions ftrace_event_type_funcs_##call = {	\
         if (ret)                                                        \
                 return ret;
 
+#undef __field_struct_ext
+#define __field_struct_ext(type, item, filter_type)                     \
+        ret = trace_define_field(event_call, #type, #item,              \
+                                 offsetof(typeof(field), item),         \
+                                 sizeof(field.item),                    \
+                                 0, filter_type);                       \
+        if (ret)                                                        \
+                return ret;
+
 #undef __field
 #define __field(type, item)     __field_ext(type, item, FILTER_OTHER)
 
+#undef __field_struct
+#define __field_struct(type, item) __field_struct_ext(type, item, FILTER_OTHER)
+
 #undef __array
 #define __array(type, item, len)                                        \
         do {                                                            \
@@ -379,6 +403,12 @@ ftrace_define_fields_##call(struct ftrace_event_call *event_call)	\
 #undef __field_ext
 #define __field_ext(type, item, filter_type)
 
+#undef __field_struct
+#define __field_struct(type, item)
+
+#undef __field_struct_ext
+#define __field_struct_ext(type, item, filter_type)
+
 #undef __array
 #define __array(type, item, len)
 
@@ -550,6 +580,9 @@ static inline notrace int ftrace_get_offsets_##call(			\
 #undef __field
 #define __field(type, item)
 
+#undef __field_struct
+#define __field_struct(type, item)
+
 #undef __array
 #define __array(type, item, len)
 
diff --git a/samples/trace_events/trace-events-sample.h b/samples/trace_events/trace-events-sample.h
index 6af373236d73..4b0113f73ee9 100644
--- a/samples/trace_events/trace-events-sample.h
+++ b/samples/trace_events/trace-events-sample.h
@@ -56,7 +56,8 @@
  * struct:  This defines the way the data will be stored in the ring buffer.
  *    There are currently two types of elements. __field and __array.
  *    a __field is broken up into (type, name). Where type can be any
- *    type but an array.
+ *    primitive type (integer, long or pointer). __field_struct() can
+ *    be any static complex data value (struct, union, but not an array).
  *    For an array. there are three fields. (type, name, size). The
  *    type of elements in the array, the name of the field and the size
  *    of the array.