[PATCH v6 07/24] tracing: Add events/ root files to trace remotes

[Steven Rostedt]

On Thu, 21 Aug 2025 09:13:55 +0100
Vincent Donnefort <vdonnefort at google.com> wrote:


> diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
> index 822cdd76e334..5065b162c8ef 100644
> --- a/kernel/trace/trace_remote.c
> +++ b/kernel/trace/trace_remote.c
> @@ -710,10 +710,118 @@ static int remote_event_callback(const char *name, umode_t *mode, void **data,
>  	return 0;
>  }
>  
> +static ssize_t remote_events_dir_enable_write(struct file *filp, const char __user *ubuf,
> +					      size_t count, loff_t *ppos)
> +{
> +	struct trace_remote *remote = file_inode(filp)->i_private;
> +	u8 enable;
> +	int i, ret;
> +
> +	ret = kstrtou8_from_user(ubuf, count, 10, &enable);
> +	if (ret)
> +		return ret;
> +
> +	guard(mutex)(&remote->lock);
> +
> +	for (i = 0; i < remote->nr_events; i++) {
> +		struct remote_event *evt = &remote->events[i];
> +
> +		trace_remote_enable_event(remote, evt, enable);
> +	}
> +
> +	return count;
> +}
> +
> +static const struct file_operations remote_events_dir_enable_fops = {
> +	.write = remote_events_dir_enable_write,

Hmm, why not a read as well? Or is it too difficult to figure out what is
enabled and what isn't.

For the main trace buffer, it's:

 0 - all disabled
 1 - all enabled
 X - some disabled some enabled


> +};
> +
> +static ssize_t
> +remote_events_dir_header_page_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
> +{
> +	struct trace_seq *s;
> +	int ret;
> +
> +	s = kmalloc(sizeof(*s), GFP_KERNEL);
> +	if (!s)
> +		return -ENOMEM;
> +
> +	trace_seq_init(s);
> +
> +	ring_buffer_print_page_header(NULL, s);
> +	ret = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, trace_seq_used(s));
> +	kfree(s);
> +
> +	return ret;
> +}
> +
> +static const struct file_operations remote_events_dir_header_page_fops = {
> +	.read = remote_events_dir_header_page_read,
> +};
> +
> +static ssize_t
> +remote_events_dir_header_event_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
> +{
> +	struct trace_seq *s;
> +	int ret;
> +
> +	s = kmalloc(sizeof(*s), GFP_KERNEL);
> +	if (!s)
> +		return -ENOMEM;
> +
> +	trace_seq_init(s);
> +
> +	ring_buffer_print_entry_header(s);
> +	ret = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, trace_seq_used(s));
> +	kfree(s);
> +
> +	return ret;
> +}
> +
> +static const struct file_operations remote_events_dir_header_event_fops = {
> +	.read = remote_events_dir_header_event_read,
> +};
> +
> +static int remote_events_dir_callback(const char *name, umode_t *mode, void **data,
> +				      const struct file_operations **fops)
> +{
> +	if (!strcmp(name, "enable")) {
> +		*mode = 0200;

As 0200 is a bit strange.

-- Steve


> +		*fops = &remote_events_dir_enable_fops;
> +		return 1;
> +	}
> +
> +	if (!strcmp(name, "header_page")) {
> +		*mode = TRACEFS_MODE_READ;
> +		*fops = &remote_events_dir_header_page_fops;
> +		return 1;
> +	}
> +
> +	if (!strcmp(name, "header_event")) {
> +		*mode = TRACEFS_MODE_READ;
> +		*fops = &remote_events_dir_header_event_fops;
> +		return 1;
> +	}
> +
> +	return 0;
> +}
> +
>  static int trace_remote_init_eventfs(const char *remote_name, struct trace_remote *remote,
>  				     struct remote_event *evt)
>  {
>  	struct eventfs_inode *eventfs = remote->eventfs;
> +	static struct eventfs_entry dir_entries[] = {
> +		{
> +			.name		= "enable",
> +			.callback	= remote_events_dir_callback,
> +		}, {
> +			.name		= "header_page",
> +			.callback	= remote_events_dir_callback,
> +		}, {
> +			.name		= "header_event",
> +			.callback	= remote_events_dir_callback,
> +		}
> +	};
>  	static struct eventfs_entry entries[] = {
>  		{
>  			.name		= "enable",
> @@ -729,7 +837,8 @@ static int trace_remote_init_eventfs(const char *remote_name, struct trace_remot
>  	bool eventfs_create = false;
>  
>  	if (!eventfs) {
> -		eventfs = eventfs_create_events_dir("events", remote->dentry, NULL, 0, NULL);
> +		eventfs = eventfs_create_events_dir("events", remote->dentry, dir_entries,
> +						    ARRAY_SIZE(dir_entries), remote);
>  		if (IS_ERR(eventfs))
>  			return PTR_ERR(eventfs);
>