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 rcu_read_lock() to safely access volatile filter strings. Signed-off-by: Aaron Tomlin <[email protected]> --- Documentation/trace/ftrace.rst | 6 ++++ kernel/trace/trace_events.c | 62 ++++++++++++++++++++++++++++++++++ 2 files changed, 68 insertions(+) diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index 639f4d95732f..27ea54bfbc52 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -684,6 +684,12 @@ 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 are enabled and have a filter applied. + + See events.rst for more information. + available_events: A list of events that can be enabled in tracing. diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index b16a5a158040..f578ee2e5c12 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -1661,6 +1661,34 @@ 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 instance + * @v: The current trace_event_file being iterated + * + * Traverses the trace_array event list and prints the system, name, + * and filter string for any event with an active filter. + * Uses RCU to safely dereference the volatile filter pointer. + */ +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; + + rcu_read_lock(); + filter = rcu_dereference(file->filter); + if (filter && filter->filter_string) { + seq_printf(m, "%s:%s\t%s\n", + call->class->system, + trace_event_name(call), + filter->filter_string); + } + rcu_read_unlock(); + + return 0; +} + #ifdef CONFIG_MODULES static int s_show(struct seq_file *m, void *v) { @@ -2488,6 +2516,7 @@ 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); @@ -2506,6 +2535,13 @@ 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, @@ -2535,6 +2571,13 @@ 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, @@ -2679,6 +2722,22 @@ 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) +{ + const struct seq_operations *seq_ops = &show_show_event_filters_seq_ops; + + return ftrace_event_open(inode, file, seq_ops); +} + static int ftrace_event_set_pid_open(struct inode *inode, struct file *file) { @@ -4399,6 +4458,9 @@ 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, -- 2.51.0
