linux-kernel - Re: [PATCH v3 5/8] stacktrace: introduce snprint_stack

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Date:	Tue, 25 Nov 2014 08:46:44 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mel Gorman <mgorman@...e.de>, Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>, Dave Hansen <dave@...1.net>,
	Michal Nazarewicz <mina86@...a86.com>,
	Jungsoo Son <jungsoo.son@....com>,
	Ingo Molnar <mingo@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 5/8] stacktrace: introduce snprint_stack_trace for
 buffer output

On Mon, Nov 24, 2014 at 02:57:52PM -0800, Andrew Morton wrote:
> On Mon, 24 Nov 2014 17:15:23 +0900 Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
> 
> > Current stacktrace only have the function for console output.
> > page_owner that will be introduced in following patch needs to print
> > the output of stacktrace into the buffer for our own output format
> > so so new function, snprint_stack_trace(), is needed.
> > 
> > ...
> >
> > +int snprint_stack_trace(char *buf, size_t size,
> > +			struct stack_trace *trace, int spaces)
> > +{
> > +	int i;
> > +	unsigned long ip;
> > +	int generated;
> > +	int total = 0;
> > +
> > +	if (WARN_ON(!trace->entries))
> > +		return 0;
> > +
> > +	for (i = 0; i < trace->nr_entries; i++) {
> > +		ip = trace->entries[i];
> > +		generated = snprintf(buf, size, "%*c[<%p>] %pS\n",
> > +				1 + spaces, ' ', (void *) ip, (void *) ip);
> > +
> > +		total += generated;
> > +
> > +		/* Assume that generated isn't a negative number */
> > +		if (generated >= size) {
> > +			buf += size;
> > +			size = 0;
> 
> Seems strange to keep looping around doing nothing.  Would it be better
> to `break' here?

generated will be added to total in each iteration even if size is 0.
snprint_stack_trace() could return accurate generated string length
by this looping.

Thanks.
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