Commit 729757b9 authored by Aaron Tomlin's avatar Aaron Tomlin Committed by Steven Rostedt (Google)
Browse files

tracing: Add show_event_filters to expose active event filters 

Currently, to audit active Ftrace event filters, userspace must
recursively traverse the events/ directory and read each individual
filter file. This is inefficient for monitoring tools and debugging.

Introduce "show_event_filters" at the trace root directory. This file
displays all events that currently have a filter applied, alongside the
actual filter string, in a consolidated system:event [tab] filter
format.

The implementation reuses the existing trace_event_file iterators to
ensure atomic traversal of the event list and utilises guard(rcu)() for
automatic, scope-based protection when accessing volatile filter
strings.

Link: https://patch.msgid.link/20260105142939.2655342-2-atomlin@atomlin.com


Signed-off-by: default avatarAaron Tomlin <atomlin@atomlin.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent e5136678

Documentation/trace/ftrace.rst

+8 −0
Original line number Diff line number Diff line
@@ -684,6 +684,14 @@ of ftrace. Here is a list of some of the key files: 


	See events.rst for more information.



  show_event_filters:



	A list of events that have filters. This shows the

	system/event pair along with the filter that is attached to

	the event.



	See events.rst for more information.



  available_events:



	A list of events that can be enabled in tracing.

kernel/trace/trace_events.c

+58 −0
Original line number Diff line number Diff line
@@ -1662,6 +1662,32 @@ static void t_stop(struct seq_file *m, void *p) 
	mutex_unlock(&event_mutex);

}



/**

 * t_show_filters - seq_file callback to display active event filters

 * @m: The seq_file interface for formatted output

 * @v: The current trace_event_file being iterated

 *

 * Identifies and prints active filters for the current event file in the

 * iteration. If a filter is applied to the current event and, if so,

 * prints the system name, event name, and the filter string.

 */

static int t_show_filters(struct seq_file *m, void *v)

{

	struct trace_event_file *file = v;

	struct trace_event_call *call = file->event_call;

	struct event_filter *filter;



	guard(rcu)();

	filter = rcu_dereference(file->filter);

	if (!filter || !filter->filter_string)

		return 0;



	seq_printf(m, "%s:%s\t%s\n", call->class->system,

		   trace_event_name(call), filter->filter_string);



	return 0;

}



#ifdef CONFIG_MODULES

static int s_show(struct seq_file *m, void *v)

{
@@ -2489,6 +2515,7 @@ ftrace_event_npid_write(struct file *filp, const char __user *ubuf, 


static int ftrace_event_avail_open(struct inode *inode, struct file *file);

static int ftrace_event_set_open(struct inode *inode, struct file *file);

static int ftrace_event_show_filters_open(struct inode *inode, struct file *file);

static int ftrace_event_set_pid_open(struct inode *inode, struct file *file);

static int ftrace_event_set_npid_open(struct inode *inode, struct file *file);

static int ftrace_event_release(struct inode *inode, struct file *file);
@@ -2507,6 +2534,13 @@ static const struct seq_operations show_set_event_seq_ops = { 
	.stop = s_stop,

};



static const struct seq_operations show_show_event_filters_seq_ops = {

	.start = t_start,

	.next = t_next,

	.show = t_show_filters,

	.stop = t_stop,

};



static const struct seq_operations show_set_pid_seq_ops = {

	.start = p_start,

	.next = p_next,
@@ -2536,6 +2570,13 @@ static const struct file_operations ftrace_set_event_fops = { 
	.release = ftrace_event_release,

};



static const struct file_operations ftrace_show_event_filters_fops = {

	.open = ftrace_event_show_filters_open,

	.read = seq_read,

	.llseek = seq_lseek,

	.release = seq_release,

};



static const struct file_operations ftrace_set_event_pid_fops = {

	.open = ftrace_event_set_pid_open,

	.read = seq_read,
@@ -2680,6 +2721,20 @@ ftrace_event_set_open(struct inode *inode, struct file *file) 
	return ret;

}



/**

 * ftrace_event_show_filters_open - open interface for set_event_filters

 * @inode: The inode of the file

 * @file: The file being opened

 *

 * Connects the set_event_filters file to the sequence operations

 * required to iterate over and display active event filters.

 */

static int

ftrace_event_show_filters_open(struct inode *inode, struct file *file)

{

	return ftrace_event_open(inode, file, &show_show_event_filters_seq_ops);

}



static int

ftrace_event_set_pid_open(struct inode *inode, struct file *file)

{
@@ -4400,6 +4455,9 @@ create_event_toplevel_files(struct dentry *parent, struct trace_array *tr) 
	if (!entry)

		return -ENOMEM;



	trace_create_file("show_event_filters", TRACE_MODE_READ, parent, tr,

			  &ftrace_show_event_filters_fops);



	nr_entries = ARRAY_SIZE(events_entries);



	e_events = eventfs_create_events_dir("events", parent, events_entries,