[RFC][PATCH 01/10] tracing: Add TRACE_DEFINE_ENUM() macro to map enums to their values

[Steven Rostedt]

From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>

Several tracepoints use the helper functions __print_symbolic() or
__print_flags() and pass in enums that do the mapping between the
binary data stored and the value to print. This works well for reading
the ASCII trace files, but when the data is read via userspace tools
such as perf and trace-cmd, the conversion of the binary value to a
human string format is lost if an enum is used, as userspace does not
have access to what the ENUM is.

For example, the tracepoint trace_tlb_flush() has:

 __print_symbolic(REC->reason,
    { TLB_FLUSH_ON_TASK_SWITCH, "flush on task switch" },
    { TLB_REMOTE_SHOOTDOWN, "remote shootdown" },
    { TLB_LOCAL_SHOOTDOWN, "local shootdown" },
    { TLB_LOCAL_MM_SHOOTDOWN, "local mm shootdown" })

Which maps the enum values to the strings they represent. But perf and
trace-cmd do no know what value TLB_LOCAL_MM_SHOOTDOWN is, and would
not be able to map it.

With TRACE_DEFINE_ENUM(), developers can place these in the event header
files and ftrace will export the value of the enum via the file:

 tracing/enum_map

By adding:

 TRACE_DEFINE_ENUM(TLB_FLUSH_ON_TASK_SWITCH);
 TRACE_DEFINE_ENUM(TLB_REMOTE_SHOOTDOWN);
 TRACE_DEFINE_ENUM(TLB_LOCAL_SHOOTDOWN);
 TRACE_DEFINE_ENUM(TLB_LOCAL_MM_SHOOTDOWN);

 $ cat /sys/kernel/debug/tracing/enum_map
TLB_FLUSH_ON_TASK_SWITCH 0
TLB_REMOTE_SHOOTDOWN 1
TLB_LOCAL_SHOOTDOWN 2
TLB_LOCAL_MM_SHOOTDOWN 3

The above can be easily parsed by userspace and it can be able to
convert the enums to their values and properly parse the enums within
the __print_symbolic() and __print_flags() helper functions.

Cc: Guilherme Cox <cox@xxxxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Xie XiuQi <xiexiuqi@xxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 include/asm-generic/vmlinux.lds.h |   5 +-
 include/linux/tracepoint.h        |   7 +++
 include/trace/ftrace.h            |  11 ++++
 kernel/trace/trace.c              | 108 +++++++++++++++++++++++++++++++++++++-
 4 files changed, 129 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index ac78910d7416..f8e8b34dc427 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -124,7 +124,10 @@
 #define FTRACE_EVENTS()	. = ALIGN(8);					\
 			VMLINUX_SYMBOL(__start_ftrace_events) = .;	\
 			*(_ftrace_events)				\
-			VMLINUX_SYMBOL(__stop_ftrace_events) = .;
+			VMLINUX_SYMBOL(__stop_ftrace_events) = .;	\
+			VMLINUX_SYMBOL(__start_ftrace_enum_maps) = .;	\
+			*(_ftrace_enum_map)				\
+			VMLINUX_SYMBOL(__stop_ftrace_enum_maps) = .;
 #else
 #define FTRACE_EVENTS()
 #endif
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index c72851328ca9..587145af3525 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -36,6 +36,11 @@ struct tracepoint {
 	struct tracepoint_func __rcu *funcs;
 };
 
+struct trace_enum_map {
+	const char		*enum_string;
+	unsigned long		enum_value;
+};
+
 extern int
 tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data);
 extern int
@@ -87,6 +92,8 @@ extern void syscall_unregfunc(void);
 
 #define PARAMS(args...) args
 
+#define TRACE_DEFINE_ENUM(x)
+
 #endif /* _LINUX_TRACEPOINT_H */
 
 /*
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 41bf65f04dd9..befa8d31672c 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -18,6 +18,14 @@
 
 #include <linux/ftrace_event.h>
 
+#undef TRACE_DEFINE_ENUM
+#define TRACE_DEFINE_ENUM(a)				\
+	static struct trace_enum_map __used __initdata	\
+	__##TRACE_SYSTEM##_##a = { #a, a };		\
+	static struct trace_enum_map __used		\
+	__attribute__((section("_ftrace_enum_map")))	\
+	*TRACE_SYSTEM##_##a = &__##TRACE_SYSTEM##_##a
+
 /*
  * DECLARE_EVENT_CLASS can be used to add a generic function
  * handlers for events. That is, if all events have the same
@@ -122,6 +130,9 @@
  * The size of an array is also encoded, in the higher 16 bits of <item>.
  */
 
+#undef TRACE_DEFINE_ENUM
+#define TRACE_DEFINE_ENUM(a)
+
 #undef __field
 #define __field(type, item)
 
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 62c6506d663f..53b449c522a7 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -123,6 +123,9 @@ enum ftrace_dump_mode ftrace_dump_on_oops;
 /* When set, tracing will stop when a WARN*() is hit */
 int __disable_trace_on_warning;
 
+/* Map of enums to their values, for "enum_map" file */
+static struct trace_enum_map *trace_enum_maps;
+
 static int tracing_set_tracer(struct trace_array *tr, const char *buf);
 
 #define MAX_TRACER_SIZE		100
@@ -3908,6 +3911,96 @@ static const struct file_operations tracing_saved_cmdlines_size_fops = {
 	.write		= tracing_saved_cmdlines_size_write,
 };
 
+static void *enum_map_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	struct trace_enum_map *ptr = v;
+
+	if (!ptr->enum_string)
+		return NULL;
+
+	ptr++;
+
+	(*pos)++;
+
+	if (!ptr->enum_string)
+		return NULL;
+
+	return ptr;
+}
+
+static void *enum_map_start(struct seq_file *m, loff_t *pos)
+{
+	struct trace_enum_map *v;
+	loff_t l = 0;
+
+	v = trace_enum_maps;
+	while (v && l < *pos) {
+		v = enum_map_next(m, v, &l);
+	}
+
+	return v;
+}
+
+static void enum_map_stop(struct seq_file *m, void *v)
+{
+}
+
+static int enum_map_show(struct seq_file *m, void *v)
+{
+	struct trace_enum_map *ptr = v;
+
+	seq_printf(m, "%s %ld\n", ptr->enum_string, ptr->enum_value);
+	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 void
+trace_insert_enum_map(struct trace_enum_map **start, struct trace_enum_map **stop)
+{
+	struct trace_enum_map **map;
+	struct trace_enum_map *map_array;
+	int len = stop - start;
+
+	if (len <= 0)
+		return;
+
+	map_array = kmalloc(sizeof(*map_array) * (len + 1), GFP_KERNEL);
+	if (!map_array) {
+		pr_warning("Unable to allocate trace enum mapping\n");
+		return;
+	}
+
+	trace_enum_maps = map_array;
+
+	for (map = start; (unsigned long)map < (unsigned long)stop; map++) {
+		*map_array = **map;
+		map_array++;
+	}
+	memset(map_array, 0, sizeof(*map_array));
+}
+
+
 static ssize_t
 tracing_set_trace_read(struct file *filp, char __user *ubuf,
 		       size_t cnt, loff_t *ppos)
@@ -6542,6 +6635,14 @@ struct dentry *tracing_init_dentry(void)
 	return tr->dir;
 }
 
+extern struct trace_enum_map *__start_ftrace_enum_maps[];
+extern struct trace_enum_map *__stop_ftrace_enum_maps[];
+
+static void __init trace_enum_init(void)
+{
+	trace_insert_enum_map(__start_ftrace_enum_maps, __stop_ftrace_enum_maps);
+}
+
 static __init int tracer_init_debugfs(void)
 {
 	struct dentry *d_tracer;
@@ -6566,6 +6667,11 @@ static __init int tracer_init_debugfs(void)
 	trace_create_file("saved_cmdlines_size", 0644, d_tracer,
 			  NULL, &tracing_saved_cmdlines_size_fops);
 
+	trace_enum_init();
+
+	trace_create_file("enum_map", 0444, d_tracer,
+			  NULL, &tracing_enum_map_fops);
+
 #ifdef CONFIG_DYNAMIC_FTRACE
 	trace_create_file("dyn_ftrace_total_info", 0444, d_tracer,
 			&ftrace_update_tot_cnt, &tracing_dyn_info_fops);
@@ -6888,7 +6994,7 @@ void __init trace_init(void)
 			tracepoint_printk = 0;
 	}
 	tracer_alloc_buffers();
-	trace_event_init();	
+	trace_event_init();
 }
 
 __init static int clear_boot_tracer(void)
-- 
2.1.4


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