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

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Date:	Tue, 24 Mar 2009 12:01:09 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Tom Zanussi <tzanussi@...il.com>
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


On Tue, 24 Mar 2009, Tom Zanussi wrote:

> 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)) {

I'm confused because it looks like it is hooked here and not above where 
we exit.

-- Steve

> > > +		filter_free_pred(pred);
> > > +		return -EINVAL;
> > > +	}
> > > +
> > > +	*ppos += cnt;
> > > +
> > > +	return cnt;
> > > +}
> > > +
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