tracing: Add enum_map file to show enums that have been mapped

Add a enum_map file in the tracing directory to see what enums have been
saved to convert in the print fmt files.

As this requires the enum mapping to be persistent in memory, it is only
created if the new config option CONFIG_TRACE_ENUM_MAP_FILE is enabled.
This is for debugging and will increase the persistent memory footprint
of the kernel.

Link: http://lkml.kernel.org/r/20150403013802.220157513@goodmis.orgReviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/Kconfig

@@ -599,6 +599,34 @@ config RING_BUFFER_STARTUP_TEST
 
 	 If unsure, say N
 
+config TRACE_ENUM_MAP_FILE
+       bool "Show enum mappings for trace events"
+       depends on TRACING
+       help
+        The "print fmt" of the trace events will show the enum names instead
+	of their values. This can cause problems for user space tools that
+	use this string to parse the raw data as user space does not know
+	how to convert the string to its value.
+
+	To fix this, there's a special macro in the kernel that can be used
+	to convert the enum into its value. If this macro is used, then the
+	print fmt strings will have the enums converted to their values.
+
+	If something does not get converted properly, this option can be
+	used to show what enums the kernel tried to convert.
+
+	This option is for debugging the enum conversions. A file is created
+	in the tracing directory called "enum_map" that will show the enum
+	names matched with their values and what trace event system they
+	belong too.
+
+	Normally, the mapping of the strings to values will be freed after
+	boot up or module load. With this option, they will not be freed, as
+	they are needed for the "enum_map" file. Enabling this option will
+	increase the memory footprint of the running kernel.
+
+	If unsure, say N
+
 endif # FTRACE
 
 endif # TRACING_SUPPORT

kernel/trace/trace.c

@@ -123,6 +123,42 @@ enum ftrace_dump_mode ftrace_dump_on_oops;
 /* When set, tracing will stop when a WARN*() is hit */
 int __disable_trace_on_warning;
 
+#ifdef CONFIG_TRACE_ENUM_MAP_FILE
+/* Map of enums to their values, for "enum_map" file */
+struct trace_enum_map_head {
+	struct module			*mod;
+	unsigned long			length;
+};
+
+union trace_enum_map_item;
+
+struct trace_enum_map_tail {
+	/*
+	 * "end" is first and points to NULL as it must be different
+	 * than "mod" or "enum_string"
+	 */
+	union trace_enum_map_item	*next;
+	const char			*end;	/* points to NULL */
+};
+
+static DEFINE_MUTEX(trace_enum_mutex);
+
+/*
+ * The trace_enum_maps are saved in an array with two extra elements,
+ * one at the beginning, and one at the end. The beginning item contains
+ * the count of the saved maps (head.length), and the module they
+ * belong to if not built in (head.mod). The ending item contains a
+ * pointer to the next array of saved enum_map items.
+ */
+union trace_enum_map_item {
+	struct trace_enum_map		map;
+	struct trace_enum_map_head	head;
+	struct trace_enum_map_tail	tail;
+};
+
+static union trace_enum_map_item *trace_enum_maps;
+#endif /* CONFIG_TRACE_ENUM_MAP_FILE */
+
 static int tracing_set_tracer(struct trace_array *tr, const char *buf);
 
 #define MAX_TRACER_SIZE		100
@@ -3908,7 +3944,169 @@ static const struct file_operations tracing_saved_cmdlines_size_fops = {
 	.write		= tracing_saved_cmdlines_size_write,
 };
 
-static void trace_insert_enum_map(struct trace_enum_map **start, int len)
+#ifdef CONFIG_TRACE_ENUM_MAP_FILE
+static union trace_enum_map_item *
+update_enum_map(union trace_enum_map_item *ptr)
+{
+	if (!ptr->map.enum_string) {
+		if (ptr->tail.next) {
+			ptr = ptr->tail.next;
+			/* Set ptr to the next real item (skip head) */
+			ptr++;
+		} else
+			return NULL;
+	}
+	return ptr;
+}
+
+static void *enum_map_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	union trace_enum_map_item *ptr = v;
+
+	/*
+	 * Paranoid! If ptr points to end, we don't want to increment past it.
+	 * This really should never happen.
+	 */
+	ptr = update_enum_map(ptr);
+	if (WARN_ON_ONCE(!ptr))
+		return NULL;
+
+	ptr++;
+
+	(*pos)++;
+
+	ptr = update_enum_map(ptr);
+
+	return ptr;
+}
+
+static void *enum_map_start(struct seq_file *m, loff_t *pos)
+{
+	union trace_enum_map_item *v;
+	loff_t l = 0;
+
+	mutex_lock(&trace_enum_mutex);
+
+	v = trace_enum_maps;
+	if (v)
+		v++;
+
+	while (v && l < *pos) {
+		v = enum_map_next(m, v, &l);
+	}
+
+	return v;
+}
+
+static void enum_map_stop(struct seq_file *m, void *v)
+{
+	mutex_unlock(&trace_enum_mutex);
+}
+
+static int enum_map_show(struct seq_file *m, void *v)
+{
+	union trace_enum_map_item *ptr = v;
+
+	seq_printf(m, "%s %ld (%s)\n",
+		   ptr->map.enum_string, ptr->map.enum_value,
+		   ptr->map.system);
+
+	return 0;
+}
+
+static const struct seq_operations tracing_enum_map_seq_ops = {
+	.start		= enum_map_start,
+	.next		= enum_map_next,
+	.stop		= enum_map_stop,
+	.show		= enum_map_show,
+};
+
+static int tracing_enum_map_open(struct inode *inode, struct file *filp)
+{
+	if (tracing_disabled)
+		return -ENODEV;
+
+	return seq_open(filp, &tracing_enum_map_seq_ops);
+}
+
+static const struct file_operations tracing_enum_map_fops = {
+	.open		= tracing_enum_map_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static inline union trace_enum_map_item *
+trace_enum_jmp_to_tail(union trace_enum_map_item *ptr)
+{
+	/* Return tail of array given the head */
+	return ptr + ptr->head.length + 1;
+}
+
+static void
+trace_insert_enum_map_file(struct module *mod, struct trace_enum_map **start,
+			   int len)
+{
+	struct trace_enum_map **stop;
+	struct trace_enum_map **map;
+	union trace_enum_map_item *map_array;
+	union trace_enum_map_item *ptr;
+
+	stop = start + len;
+
+	/*
+	 * The trace_enum_maps contains the map plus a head and tail item,
+	 * where the head holds the module and length of array, and the
+	 * tail holds a pointer to the next list.
+	 */
+	map_array = kmalloc(sizeof(*map_array) * (len + 2), GFP_KERNEL);
+	if (!map_array) {
+		pr_warning("Unable to allocate trace enum mapping\n");
+		return;
+	}
+
+	mutex_lock(&trace_enum_mutex);
+
+	if (!trace_enum_maps)
+		trace_enum_maps = map_array;
+	else {
+		ptr = trace_enum_maps;
+		for (;;) {
+			ptr = trace_enum_jmp_to_tail(ptr);
+			if (!ptr->tail.next)
+				break;
+			ptr = ptr->tail.next;
+
+		}
+		ptr->tail.next = map_array;
+	}
+	map_array->head.mod = mod;
+	map_array->head.length = len;
+	map_array++;
+
+	for (map = start; (unsigned long)map < (unsigned long)stop; map++) {
+		map_array->map = **map;
+		map_array++;
+	}
+	memset(map_array, 0, sizeof(*map_array));
+
+	mutex_unlock(&trace_enum_mutex);
+}
+
+static void trace_create_enum_file(struct dentry *d_tracer)
+{
+	trace_create_file("enum_map", 0444, d_tracer,
+			  NULL, &tracing_enum_map_fops);
+}
+
+#else /* CONFIG_TRACE_ENUM_MAP_FILE */
+static inline void trace_create_enum_file(struct dentry *d_tracer) { }
+static inline void trace_insert_enum_map_file(struct module *mod,
+			      struct trace_enum_map **start, int len) { }
+#endif /* !CONFIG_TRACE_ENUM_MAP_FILE */
+
+static void trace_insert_enum_map(struct module *mod,
+				  struct trace_enum_map **start, int len)
 {
 	struct trace_enum_map **map;
 
@@ -3918,6 +4116,8 @@ static void trace_insert_enum_map(struct trace_enum_map **start, int len)
 	map = start;
 
 	trace_event_enum_update(map, len);
+
+	trace_insert_enum_map_file(mod, start, len);
 }
 
 static ssize_t
@@ -6562,7 +6762,7 @@ static void __init trace_enum_init(void)
 	int len;
 
 	len = __stop_ftrace_enum_maps - __start_ftrace_enum_maps;
-	trace_insert_enum_map(__start_ftrace_enum_maps, len);
+	trace_insert_enum_map(NULL, __start_ftrace_enum_maps, len);
 }
 
 #ifdef CONFIG_MODULES
@@ -6578,9 +6778,41 @@ static void trace_module_add_enums(struct module *mod)
 	if (trace_module_has_bad_taint(mod))
 		return;
 
-	trace_insert_enum_map(mod->trace_enums, mod->num_trace_enums);
+	trace_insert_enum_map(mod, mod->trace_enums, mod->num_trace_enums);
 }
 
+#ifdef CONFIG_TRACE_ENUM_MAP_FILE
+static void trace_module_remove_enums(struct module *mod)
+{
+	union trace_enum_map_item *map;
+	union trace_enum_map_item **last = &trace_enum_maps;
+
+	if (!mod->num_trace_enums)
+		return;
+
+	mutex_lock(&trace_enum_mutex);
+
+	map = trace_enum_maps;
+
+	while (map) {
+		if (map->head.mod == mod)
+			break;
+		map = trace_enum_jmp_to_tail(map);
+		last = &map->tail.next;
+		map = map->tail.next;
+	}
+	if (!map)
+		goto out;
+
+	*last = trace_enum_jmp_to_tail(map)->tail.next;
+	kfree(map);
+ out:
+	mutex_unlock(&trace_enum_mutex);
+}
+#else
+static inline void trace_module_remove_enums(struct module *mod) { }
+#endif /* CONFIG_TRACE_ENUM_MAP_FILE */
+
 static int trace_module_notify(struct notifier_block *self,
 			       unsigned long val, void *data)
 {
@@ -6590,6 +6822,9 @@ static int trace_module_notify(struct notifier_block *self,
 	case MODULE_STATE_COMING:
 		trace_module_add_enums(mod);
 		break;
+	case MODULE_STATE_GOING:
+		trace_module_remove_enums(mod);
+		break;
 	}
 
 	return 0;
@@ -6599,7 +6834,7 @@ static struct notifier_block trace_module_nb = {
 	.notifier_call = trace_module_notify,
 	.priority = 0,
 };
-#endif
+#endif /* CONFIG_MODULES */
 
 static __init int tracer_init_debugfs(void)
 {
@@ -6627,6 +6862,8 @@ static __init int tracer_init_debugfs(void)
 
 	trace_enum_init();
 
+	trace_create_enum_file(d_tracer);
+
 #ifdef CONFIG_MODULES
 	register_module_notifier(&trace_module_nb);
 #endif