linux-kernel - Re: [PATCH 19/22] perf tools: Add filename__read

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Date:	Mon, 25 Nov 2013 16:17:35 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH 19/22] perf tools: Add filename__read_str util function

On Sat, Nov 23, 2013 at 12:43:59AM +0900, Namhyung Kim wrote:
> 2013-11-21 (목), 12:01 +0100, Jiri Olsa:
> > Adding filename__read_str util function to read
> > text file and return it in the char array.
> > 
> > The interface is:
> >   int filename__read_str(const char *filename, char **buf, size_t *sizep)
> > 
> >   Returns 0/-1 if the read suceeded/fail respectively.
> > 
> >   buf  - place to store the data pointer
> >   size - place to store data size
> 
> [SNIP]
> > +int filename__read_str(const char *filename, char **buf, size_t *sizep)
> > +{
> > +	size_t size = 0, alloc_size = 0;
> > +	void *bf = NULL, *nbf;
> > +	int fd, n, err = 0;
> > +
> > +	fd = open(filename, O_RDONLY);
> > +	if (fd < 0)
> > +		return -errno;
> > +
> > +	do {
> > +		if (size == alloc_size) {
> > +			alloc_size += BUFSIZ;
> > +			nbf = realloc(bf, alloc_size);
> > +			if (!nbf) {
> > +				err = -ENOMEM;
> > +				break;
> > +			}
> > +
> > +			bf = nbf;
> > +		}
> > +
> > +		n = read(fd, bf + size, BUFSIZ);
> 
> Shouldn't it be "read(fd, bf + size, alloc_size - size)"?
> Otherwise there might be a problem if read() returned early for some
> reason with small size and then retry with a full BUFSIZ..
> 
> 
> > +		if (n < 0) {
> > +			err = 0;
> 
> I think it needs to check the size also since read() might fail at the
> first invocation.  What about this?
> 
> 		if (n < 0) {
> 			if (size)
> 				err = 0;
> 			else
> 				err = -errno;
> 

ok, added.. plus warning in the 'if (size)' leg,
because we're returning data even if we failed.

thanks,
jirka
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