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

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Date:	Wed, 25 Mar 2009 00:26:07 -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 4/4] tracing: add per-subsystem filtering

On Tue, 2009-03-24 at 12:29 -0400, Steven Rostedt wrote:
> On Tue, 24 Mar 2009, Tom Zanussi wrote:
> > > > +
> > > > +static ssize_t
> > > > +subsystem_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
> > > > +		       loff_t *ppos)
> > > > +{
> > > > +	struct event_subsystem *system = 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_subsystem_preds(system);
> > > 
> > > is "system" correct here?
> > 
> > Do you mean the naming i.e. would be better as "subsystem"?  Otherwise,
> > I think it's correct.
> 
> No, I'm just confused how the system could see the pred before it was 
> added below.

Again, in this case the pred is only used to flag clearing and never
gets added.

Tom

> 
> -- Steve
> 
> > 
> > > 
> > > > +		return cnt;
> > > > +	}
> > > > +
> > > > +	if (filter_add_subsystem_pred(system, pred)) {
> > > > +		filter_free_pred(pred);
> > > > +		return -EINVAL;
> > > > +	}
> > > > +
> > > > +	*ppos += cnt;
> > > > +
> > > > +	return cnt;
> > > > +}
> > > > +

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