linux-kernel - Re: [PATCH v3 15/33] tracing: Add simple expression support to hist triggers

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Date:   Wed, 11 Oct 2017 09:08:20 -0500
From:   Tom Zanussi <tom.zanussi@...ux.intel.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     rostedt@...dmis.org, tglx@...utronix.de, mhiramat@...nel.org,
        vedang.patel@...el.com, bigeasy@...utronix.de,
        joel.opensrc@...il.com, joelaf@...gle.com,
        mathieu.desnoyers@...icios.com, baohong.liu@...el.com,
        rajvi.jingar@...el.com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org, kernel-team@....com
Subject: Re: [PATCH v3 15/33] tracing: Add simple expression support to hist
 triggers

On Mon, 2017-10-09 at 21:54 +0900, Namhyung Kim wrote:
> On Fri, Sep 22, 2017 at 02:59:55PM -0500, Tom Zanussi wrote:
> > Add support for simple addition, subtraction, and unary expressions
> > (-(expr) and expr, where expr = b-a, a+b, a+b+c) to hist triggers, in
> > order to support a minimal set of useful inter-event calculations.
> > 
> > These operations are needed for calculating latencies between events
> > (timestamp1-timestamp0) and for combined latencies (latencies over 3
> > or more events).
> > 
> > In the process, factor out some common code from key and value
> > parsing.
> > 
> > Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
> > ---
> 
> [SNIP]
> > +static struct hist_field *parse_unary(struct hist_trigger_data *hist_data,
> > +				      struct trace_event_file *file,
> > +				      char *str, unsigned long flags,
> > +				      char *var_name, unsigned int level)
> > +{
> > +	struct hist_field *operand1, *expr = NULL;
> > +	unsigned long operand_flags;
> > +	int ret = 0;
> > +	char *s;
> > +
> > +	// we support only -(xxx) i.e. explicit parens required
> > +
> > +	if (level > 2) {
> > +		ret = -EINVAL;
> > +		goto free;
> > +	}
> > +
> > +	str++; // skip leading '-'
> > +
> > +	s = strchr(str, '(');
> > +	if (s)
> > +		str++;
> > +	else {
> > +		ret = -EINVAL;
> > +		goto free;
> > +	}
> > +
> > +	s = strchr(str, ')');
> > +	if (s)
> > +		*s = '\0';
> > +	else {
> > +		ret = -EINVAL; // no closing ')'
> > +		goto free;
> > +	}
> > +
> > +	strsep(&str, "(");
> > +	if (!str) {
> > +		ret = -EINVAL;
> > +		goto free;
> > +	}
> > +
> > +	flags |= HIST_FIELD_FL_EXPR;
> > +	expr = create_hist_field(hist_data, NULL, flags, var_name);
> > +	if (!expr) {
> > +		ret = -ENOMEM;
> > +		goto free;
> > +	}
> > +
> > +	operand_flags = 0;
> > +	operand1 = parse_expr(hist_data, file, str, operand_flags, NULL, ++level);
> > +	if (IS_ERR(operand1)) {
> > +		ret = PTR_ERR(operand1);
> > +		goto free;
> > +	}
> > +
> > +	expr->fn = hist_field_unary_minus;
> > +	expr->operands[0] = operand1;
> > +	expr->operator = FIELD_OP_UNARY_MINUS;
> > +	expr->name = expr_str(expr, 0);
> > +
> > +	return expr;
> > + free:
> 
> Missing destroy_hist_field(expr, 0)?
> 

Yep, will add, thanks.

Tom