linux-kernel - Re: [PATCH 3/4] tracing: add per-event filtering

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Message-Id: <1237879085.8339.64.camel@charm-linux>
Date:	Tue, 24 Mar 2009 02:18:05 -0500
From:	Tom Zanussi <tzanussi@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frédéric Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 3/4] tracing: add per-event filtering

Hi,

On Mon, 2009-03-23 at 14:06 -0400, Steven Rostedt wrote:
> On Sun, 22 Mar 2009, Tom Zanussi wrote:
> >  
> > +static ssize_t
> > +event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
> > +		  loff_t *ppos)
> > +{
> > +	struct ftrace_event_call *call = filp->private_data;
> > +	struct trace_seq *s;
> > +	int r;
> > +
> > +	if (*ppos)
> > +		return 0;
> > +
> > +	s = kmalloc(sizeof(*s), GFP_KERNEL);
> > +	if (!s)
> > +		return -ENOMEM;
> > +
> > +	trace_seq_init(s);
> > +
> > +	r = filter_print_preds(call->preds, s->buffer);
> 
> You're not using any of the features of the trace_seq structure.
> Might as well just allocate your own buffer.
> 

Yeah, it make more sense to use the trace_seq features than do it
myself.  I just posted a patch to do that.

> > +	r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, r);
> > +
> > +	kfree(s);
> > +
> > +	return r;
> > +}
> > +
> > +static ssize_t
> > +event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
> > +		   loff_t *ppos)
> > +{
> > +	struct ftrace_event_call *call = filp->private_data;
> > +	char buf[64], *pbuf = buf;
> > +	struct filter_pred *pred;
> > +	int err;
> > +
> > +	if (cnt >= sizeof(buf))
> > +		return -EINVAL;
> > +
> > +	if (copy_from_user(&buf, ubuf, cnt))
> > +		return -EFAULT;
> > +
> > +	pred = kzalloc(sizeof(*pred), GFP_KERNEL);
> > +	if (!pred)
> > +		return -ENOMEM;
> > +
> > +	err = filter_parse(&pbuf, pred);
> > +	if (err < 0) {
> > +		filter_free_pred(pred);
> > +		return err;
> > +	}
> > +
> > +	if (pred->clear) {
> > +		filter_free_preds(call);
> 
> The above is very confusing. Why are we passing in "call"?

The preds are attached to the call, so it makes sense to me to pass in
the call.  I could just pass in the preds directly, if that makes it
less confusing...

> 
> > +		return cnt;
> > +	}
> > +
> > +	if (filter_add_pred(call, pred)) {
> > +		filter_free_pred(pred);
> > +		return -EINVAL;
> > +	}
> > +
> > +	*ppos += cnt;
> > +
> > +	return cnt;
> > +}
> > +
> >  static const struct seq_operations show_event_seq_ops = {
> >  	.start = t_start,
> >  	.next = t_next,
> > @@ -504,6 +569,12 @@ static const struct file_operations ftrace_event_id_fops = {
> >  	.read = event_id_read,
> >  };
> >  
> > +static const struct file_operations ftrace_event_filter_fops = {
> > +	.open = tracing_open_generic,
> > +	.read = event_filter_read,
> > +	.write = event_filter_write,
> > +};
> > +
> >  static struct dentry *event_trace_events_dir(void)
> >  {
> >  	static struct dentry *d_tracer;
> > @@ -619,6 +690,12 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events)
> >  		}
> >  	}
> >  
> > +	entry = debugfs_create_file("filter", 0444, call->dir, call,
> > +				    &ftrace_event_filter_fops);
> > +	if (!entry)
> > +		pr_warning("Could not create debugfs "
> > +			   "'%s/filter' entry\n", call->name);
> > +
> >  	/* A trace may not want to export its format */
> >  	if (!call->show_format)
> >  		return 0;
> 
> [...]
> 
> > +
> > diff --git a/kernel/trace/trace_events_stage_3.h b/kernel/trace/trace_events_stage_3.h
> > index 468938f..ebf215e 100644
> > --- a/kernel/trace/trace_events_stage_3.h
> > +++ b/kernel/trace/trace_events_stage_3.h
> > @@ -204,6 +204,7 @@ static struct ftrace_event_call event_##call;				\
> >  									\
> >  static void ftrace_raw_event_##call(proto)				\
> >  {									\
> > +	struct ftrace_event_call *call = &event_##call;			\
> >  	struct ring_buffer_event *event;				\
> >  	struct ftrace_raw_##call *entry;				\
> >  	unsigned long irq_flags;					\
> > @@ -222,6 +223,9 @@ static void ftrace_raw_event_##call(proto)				\
> >  	assign;								\
> >  									\
> >  	trace_current_buffer_unlock_commit(event, irq_flags, pc);	\
> > +									\
> > +	if (call->preds && !filter_match_preds(call, entry))		\
> > +		ring_buffer_event_discard(event);			\
> >  }									\
> 
> Again, this would need to be within the commit.
> 

Yeah, Frédéric already posted a patch to do that.

Thanks for your comments!

Tom

> -- Steve
> 
> >  									\
> >  static int ftrace_raw_reg_event_##call(void)				\
> > -- 
> > 1.5.6.3
> > 
> > 
> > 
> > 
> > 

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