linux-kernel - Re: [PATCH 5/9] perf util: Handle failure case in trace

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Date:	Tue, 19 Mar 2013 21:54:34 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 5/9] perf util: Handle failure case in trace_report()

On Wed, 2013-03-20 at 10:12 +0900, Namhyung Kim wrote:

> >> +++ b/tools/perf/util/trace-event-read.c
> >> @@ -293,7 +293,10 @@ ssize_t trace_report(int fd, struct pevent **ppevent, bool __repipe)
> >>  	int show_version = 0;
> >>  	int show_funcs = 0;
> >>  	int show_printk = 0;
> >> -	ssize_t size;
> >> +	ssize_t size = -1;
> >> +	struct pevent *pevent;
> >> +
> >> +	*ppevent = NULL;
> >>  
> >>  	calc_data_size = 1;
> >>  	repipe = __repipe;
> >> @@ -317,34 +320,38 @@ ssize_t trace_report(int fd, struct pevent **ppevent, bool __repipe)
> >>  	file_bigendian = buf[0];
> >>  	host_bigendian = bigendian();
> >>  
> >> -	*ppevent = read_trace_init(file_bigendian, host_bigendian);
> >> -	if (*ppevent == NULL)
> >> -		die("read_trace_init failed");
> >> +	pevent = read_trace_init(file_bigendian, host_bigendian);
> >> +	if (pevent == NULL) {
> >
> > Shouldn't we still set *ppevent to NULL? Or will the user now need to
> > make sure that its pevent is NULL and always check for error?
> 
> I thought it's impossible to check return value for error since we don't
> know how large a tracing data is, so I decided to init *ppevent to NULL
> at the beginning and set it to a valid pevent right before return.  Thus
> user need to check NULL before using it.
> 
> In the above case of perf_event__process_tracing_data(), it's a pipe
> mode and we can know its size since it's saved in a temp file.
> 

My fault, I missed the addition of *ppevent = NULL at the beginning.
Ignore this comment.

-- Steve


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