tracing: add hierarchical enabling of events

With the current event directory, you can only enable individual events.
The file debugfs/tracing/set_event is used to be able to enable or
disable several events at once. But that can still be awkward.

This patch adds hierarchical enabling of events. That is, each directory
in debugfs/tracing/events has an "enable" file. This file can enable
or disable all events within the directory and below.

 # echo 1 > /debugfs/tracing/events/enable

will enable all events.

 # echo 1 > /debugfs/tracing/events/sched/enable

will enable all events in the sched subsystem.

 # echo 1 > /debugfs/tracing/events/enable
 # echo 0 > /debugfs/tracing/events/irq/enable

will enable all events, but then disable just the irq subsystem events.

When reading one of these enable files, there are four results:

 0 - all events this file affects are disabled
 1 - all events this file affects are enabled
 X - there is a mixture of events enabled and disabled
 ? - this file does not affect any event

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_events.c

@@ -400,6 +400,133 @@ event_enable_write(struct file *filp, const char __user *ubuf, size_t cnt,
 	return cnt;
 }
 
+static ssize_t
+system_enable_read(struct file *filp, char __user *ubuf, size_t cnt,
+		   loff_t *ppos)
+{
+	const char *system = filp->private_data;
+	struct ftrace_event_call *call;
+	char buf[2];
+	int set = -1;
+	int all = 0;
+	int ret;
+
+	if (system[0] == '*')
+		all = 1;
+
+	mutex_lock(&event_mutex);
+	list_for_each_entry(call, &ftrace_events, list) {
+		if (!call->name || !call->regfunc)
+			continue;
+
+		if (!all && strcmp(call->system, system) != 0)
+			continue;
+
+		/*
+		 * We need to find out if all the events are set
+		 * or if all events or cleared, or if we have
+		 * a mixture.
+		 */
+		if (call->enabled) {
+			switch (set) {
+			case -1:
+				set = 1;
+				break;
+			case 0:
+				set = 2;
+				break;
+			}
+		} else {
+			switch (set) {
+			case -1:
+				set = 0;
+				break;
+			case 1:
+				set = 2;
+				break;
+			}
+		}
+		/*
+		 * If we have a mixture, no need to look further.
+		 */
+		if (set == 2)
+			break;
+	}
+	mutex_unlock(&event_mutex);
+
+	buf[1] = '\n';
+	switch (set) {
+	case 0:
+		buf[0] = '0';
+		break;
+	case 1:
+		buf[0] = '1';
+		break;
+	case 2:
+		buf[0] = 'X';
+		break;
+	default:
+		buf[0] = '?';
+	}
+
+	ret = simple_read_from_buffer(ubuf, cnt, ppos, buf, 2);
+
+	return ret;
+}
+
+static ssize_t
+system_enable_write(struct file *filp, const char __user *ubuf, size_t cnt,
+		    loff_t *ppos)
+{
+	const char *system = filp->private_data;
+	unsigned long val;
+	char *command;
+	char buf[64];
+	ssize_t ret;
+
+	if (cnt >= sizeof(buf))
+		return -EINVAL;
+
+	if (copy_from_user(&buf, ubuf, cnt))
+		return -EFAULT;
+
+	buf[cnt] = 0;
+
+	ret = strict_strtoul(buf, 10, &val);
+	if (ret < 0)
+		return ret;
+
+	ret = tracing_update_buffers();
+	if (ret < 0)
+		return ret;
+
+	switch (val) {
+	case 0:
+	case 1:
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	command = kstrdup(system, GFP_KERNEL);
+	if (!command)
+		return -ENOMEM;
+
+	ret = ftrace_set_clr_event(command, val);
+	if (ret)
+		goto out_free;
+
+	ret = cnt;
+
+ out_free:
+	kfree(command);
+
+	*ppos += cnt;
+
+	return ret;
+}
+
 extern char *__bad_type_size(void);
 
 #undef FIELD
@@ -686,6 +813,12 @@ static const struct file_operations ftrace_subsystem_filter_fops = {
 	.write = subsystem_filter_write,
 };
 
+static const struct file_operations ftrace_system_enable_fops = {
+	.open = tracing_open_generic,
+	.read = system_enable_read,
+	.write = system_enable_write,
+};
+
 static const struct file_operations ftrace_show_header_fops = {
 	.open = tracing_open_generic,
 	.read = show_header,
@@ -768,6 +901,10 @@ event_subsystem_dir(const char *name, struct dentry *d_events)
 			   "'%s/filter' entry\n", name);
 	}
 
+	entry = trace_create_file("enable", 0644, system->entry,
+				  (void *)system->name,
+				  &ftrace_system_enable_fops);
+
 	return system->entry;
 }
 
@@ -1041,6 +1178,9 @@ static __init int event_trace_init(void)
 			  ring_buffer_print_entry_header,
 			  &ftrace_show_header_fops);
 
+	trace_create_file("enable", 0644, d_events,
+			  "*:*", &ftrace_system_enable_fops);
+
 	for_each_event(call, __start_ftrace_events, __stop_ftrace_events) {
 		/* The linker may leave blanks */
 		if (!call->name)