tracing/events: introduce __dynamic_array()

__string() is limited:

  - it's a char array, but we may want to define array with other types
  - a source string should be available, but we may just know the string size

We introduce __dynamic_array() to break those limitations, and __string()
becomes a wrapper of it. As a side effect, now __get_str() can be used
in TP_fast_assign but not only TP_print.

Take XFS for example, we have the string length in the dirent, but the
string itself is not NULL-terminated, so __dynamic_array() can be used:

TRACE_EVENT(xfs_dir2,
	TP_PROTO(struct xfs_da_args *args),
	TP_ARGS(args),

	TP_STRUCT__entry(
		__field(int, namelen)
		__dynamic_array(char, name, args->namelen + 1)
		...
	),

	TP_fast_assign(
		char *name = __get_str(name);

		if (args->namelen)
			memcpy(name, args->name, args->namelen);
		name[args->namelen] = '\0';

		__entry->namelen = args->namelen;
	),

	TP_printk("name %.*s namelen %d",
		  __entry->namelen ? __get_str(name) : NULL
		  __entry->namelen)
);

[ Impact: allow defining dynamic size arrays ]
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A2384D2.3080403@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

include/trace/ftrace.h

@@ -18,14 +18,17 @@
 
 #include <linux/ftrace_event.h>
 
+#undef __field
+#define __field(type, item)		type	item;
+
 #undef __array
 #define __array(type, item, len)	type	item[len];
 
-#undef __field
-#define __field(type, item)		type	item;
+#undef __dynamic_array
+#define __dynamic_array(type, item, len) unsigned short __data_loc_##item;
 
 #undef __string
-#define __string(item, src)		unsigned short	__str_loc_##item;
+#define __string(item, src) __dynamic_array(char, item, -1)
 
 #undef TP_STRUCT__entry
 #define TP_STRUCT__entry(args...) args
@@ -35,7 +38,7 @@
 	struct ftrace_raw_##name {				\
 		struct trace_entry	ent;			\
 		tstruct						\
-		char			__str_data[0];		\
+		char			__data[0];		\
 	};							\
 	static struct ftrace_event_call event_##name
 
@@ -47,30 +50,31 @@
  *
  * Include the following:
  *
- * struct ftrace_str_offsets_<call> {
- *	int				<str1>;
- *	int				<str2>;
+ * struct ftrace_data_offsets_<call> {
+ *	int				<item1>;
+ *	int				<item2>;
  *	[...]
  * };
  *
- * The __string() macro will create each int <str>, this is to
- * keep the offset of each string from the beggining of the event
- * once we perform the strlen() of the src strings.
- *
+ * The __dynamic_array() macro will create each int <item>, this is
+ * to keep the offset of each array from the beginning of the event.
  */
 
+#undef __field
+#define __field(type, item);
+
 #undef __array
 #define __array(type, item, len)
 
-#undef __field
-#define __field(type, item);
+#undef __dynamic_array
+#define __dynamic_array(type, item, len)	int item;
 
 #undef __string
-#define __string(item, src)	int item;
+#define __string(item, src) __dynamic_array(char, item, -1)
 
 #undef TRACE_EVENT
 #define TRACE_EVENT(call, proto, args, tstruct, assign, print)		\
-	struct ftrace_str_offsets_##call {				\
+	struct ftrace_data_offsets_##call {				\
 		tstruct;						\
 	};
 
@@ -119,8 +123,12 @@
 #undef TP_printk
 #define TP_printk(fmt, args...) fmt "\n", args
 
+#undef __get_dynamic_array
+#define __get_dynamic_array(field)	\
+		((void *)__entry + __entry->__data_loc_##field)
+
 #undef __get_str
-#define __get_str(field)	((char *)__entry + __entry->__str_loc_##field)
+#define __get_str(field) (char *)__get_dynamic_array(field)
 
 #undef __print_flags
 #define __print_flags(flag, delim, flag_array...)			\
@@ -207,16 +215,19 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags)	\
 	if (!ret)							\
 		return 0;
 
-#undef __string
-#define __string(item, src)						       \
-	ret = trace_seq_printf(s, "\tfield:__str_loc " #item ";\t"	       \
+#undef __dynamic_array
+#define __dynamic_array(type, item, len)				       \
+	ret = trace_seq_printf(s, "\tfield:__data_loc " #item ";\t"	       \
 			       "offset:%u;\tsize:%u;\n",		       \
 			       (unsigned int)offsetof(typeof(field),	       \
-					__str_loc_##item),		       \
-			       (unsigned int)sizeof(field.__str_loc_##item));  \
+					__data_loc_##item),		       \
+			       (unsigned int)sizeof(field.__data_loc_##item)); \
 	if (!ret)							       \
 		return 0;
 
+#undef __string
+#define __string(item, src) __dynamic_array(char, item, -1)
+
 #undef __entry
 #define __entry REC
 
@@ -260,11 +271,14 @@ ftrace_format_##call(struct trace_seq *s)				\
 	if (ret)							\
 		return ret;
 
+#undef __dynamic_array
+#define __dynamic_array(type, item, len)				       \
+	ret = trace_define_field(event_call, "__data_loc" "[" #type "]", #item,\
+				offsetof(typeof(field), __data_loc_##item),    \
+				 sizeof(field.__data_loc_##item), 0);
+
 #undef __string
-#define __string(item, src)						       \
-	ret = trace_define_field(event_call, "__str_loc", #item,	       \
-				offsetof(typeof(field), __str_loc_##item),     \
-				 sizeof(field.__str_loc_##item), 0);
+#define __string(item, src) __dynamic_array(char, item, -1)
 
 #undef TRACE_EVENT
 #define TRACE_EVENT(call, proto, args, tstruct, func, print)		\
@@ -288,6 +302,43 @@ ftrace_define_fields_##call(void)					\
 
 #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
 
+/*
+ * remember the offset of each array from the beginning of the event.
+ */
+
+#undef __entry
+#define __entry entry
+
+#undef __field
+#define __field(type, item)
+
+#undef __array
+#define __array(type, item, len)
+
+#undef __dynamic_array
+#define __dynamic_array(type, item, len)				\
+	__data_offsets->item = __data_size +				\
+			       offsetof(typeof(*entry), __data);	\
+	__data_size += (len) * sizeof(type);
+
+#undef __string
+#define __string(item, src) __dynamic_array(char, item, strlen(src) + 1)       \
+
+#undef TRACE_EVENT
+#define TRACE_EVENT(call, proto, args, tstruct, assign, print)		\
+static inline int ftrace_get_offsets_##call(				\
+	struct ftrace_data_offsets_##call *__data_offsets, proto)       \
+{									\
+	int __data_size = 0;						\
+	struct ftrace_raw_##call __maybe_unused *entry;			\
+									\
+	tstruct;							\
+									\
+	return __data_size;						\
+}
+
+#include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
+
 /*
  * Stage 4 of the trace events.
  *
@@ -432,15 +483,15 @@ static void ftrace_profile_disable_##call(struct ftrace_event_call *event_call)\
 #undef __array
 #define __array(type, item, len)
 
+#undef __dynamic_array
+#define __dynamic_array(type, item, len)				\
+	__entry->__data_loc_##item = __data_offsets.item;
+
 #undef __string
-#define __string(item, src)						\
-	__str_offsets.item = __str_size +				\
-			     offsetof(typeof(*entry), __str_data);	\
-	__str_size += strlen(src) + 1;
+#define __string(item, src) __dynamic_array(char, item, -1)       	\
 
 #undef __assign_str
 #define __assign_str(dst, src)						\
-	__entry->__str_loc_##dst = __str_offsets.dst;			\
 	strcpy(__get_str(dst), src);
 
 #undef TRACE_EVENT
@@ -451,26 +502,29 @@ static struct ftrace_event_call event_##call;				\
 									\
 static void ftrace_raw_event_##call(proto)				\
 {									\
-	struct ftrace_str_offsets_##call __maybe_unused __str_offsets;	\
+	struct ftrace_data_offsets_##call __maybe_unused __data_offsets;\
 	struct ftrace_event_call *event_call = &event_##call;		\
 	struct ring_buffer_event *event;				\
 	struct ftrace_raw_##call *entry;				\
 	unsigned long irq_flags;					\
-	int __str_size = 0;						\
+	int __data_size;						\
 	int pc;								\
 									\
 	local_save_flags(irq_flags);					\
 	pc = preempt_count();						\
 									\
-	tstruct;							\
+	__data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
 									\
 	event = trace_current_buffer_lock_reserve(event_##call.id,	\
-				 sizeof(struct ftrace_raw_##call) + __str_size,\
+				 sizeof(*entry) + __data_size,		\
 				 irq_flags, pc);			\
 	if (!event)							\
 		return;							\
 	entry	= ring_buffer_event_data(event);			\
 									\
+									\
+	tstruct								\
+									\
 	{ assign; }							\
 									\
 	if (!filter_current_check_discard(event_call, entry, event))	\

kernel/trace/trace_events_filter.c

@@ -478,12 +478,12 @@ enum {
 
 static int is_string_field(const char *type)
 {
+	if (strstr(type, "__data_loc") && strstr(type, "char"))
+		return FILTER_DYN_STRING;
+
 	if (strchr(type, '[') && strstr(type, "char"))
 		return FILTER_STATIC_STRING;
 
-	if (!strcmp(type, "__str_loc"))
-		return FILTER_DYN_STRING;
-
 	return 0;
 }