linux-kernel - Re: [PATCH 4/8] perf tools: Introduce struct perf

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Date:	Thu, 26 Dec 2013 09:51:25 -0500
From:	David Ahern <dsahern@...il.com>
To:	Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	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>, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH 4/8] perf tools: Introduce struct perf_log

On 12/26/13, 12:38 AM, Namhyung Kim wrote:
> diff --git a/tools/perf/util/log.c b/tools/perf/util/log.c
> new file mode 100644
> index 000000000000..3838d49f82de
> --- /dev/null
> +++ b/tools/perf/util/log.c
> @@ -0,0 +1,105 @@
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include "util/debug.h"
> +
> +#define LINEMAP_GROW  128
> +
> +struct perf_log perf_log = {
> +	.seen_newline = true,
> +};
> +
> +int perf_log_init(void)

Why return int if the rc is not checked? Failure here is not going to 
stop the perf command right?

> +{
> +	FILE *fp;
> +	char name[] = "/tmp/perf-log-XXXXXX";
> +	int fd = mkstemp(name);
> +
> +	if (fd < 0)
> +		return -1;
> +
> +	fp = fdopen(fd, "r+");
> +	if (fp == NULL) {
> +		close(fd);
> +		return -1;
> +	}
> +
> +	perf_log.fp = fp;

Add 'unlink(name);' here to ensure the file is removed regardless of how 
perf terminates.

> +
> +	return 0;
> +}
> +
> +int perf_log_exit(void)
> +{
> +	FILE *fp = perf_log.fp;
> +	if (fp)
> +		fclose(fp);
> +
> +	free(perf_log.linemap);
> +
> +	perf_log.fp = NULL;
> +	perf_log.linemap = NULL;
> +	return 0;
> +}
> +
> +static int grow_linemap(struct perf_log *log)
> +{
> +	off_t *newmap;
> +	int newsize = log->nr_alloc + LINEMAP_GROW;
> +
> +	newmap = realloc(log->linemap, newsize * sizeof(*log->linemap));
> +	if (newmap == NULL)
> +		return -1;
> +
> +	log->nr_alloc = newsize;
> +	log->linemap = newmap;
> +	return 0;
> +}

What's the point of linemap?

> +
> +static int __add_to_linemap(struct perf_log *log, off_t idx)
> +{
> +	if (log->lines == log->nr_alloc)
> +		if (grow_linemap(log) < 0)
> +			return -1;
> +
> +	log->linemap[log->lines++] = idx;
> +	return 0;
> +}
> +
> +static void add_to_linemap(struct perf_log *log, const char *msg, off_t base)
> +{
> +	const char *pos;
> +
> +	if (strlen(msg) == 0)
> +		return;
> +
> +	if (log->seen_newline) {
> +		if (__add_to_linemap(log, base) < 0)
> +			return;
> +	}
> +
> +	if ((pos = strchr(msg, '\n')) != NULL) {
> +		log->seen_newline = true;
> +		pos++;
> +		add_to_linemap(log, pos, base + (pos - msg));
> +	} else {
> +		log->seen_newline = false;
> +	}
> +}
> +
> +void perf_log_add(const char *msg)
> +{
> +	FILE *fp = perf_log.fp;

Don't assume every user of libperf calls perf_log_init() or that the 
file was actually created. i.e., add 'if (fp == NULL) return;'


> +	off_t offset = ftello(fp);
> +
> +	add_to_linemap(&perf_log, msg, offset);
> +
> +	fwrite(msg, 1, strlen(msg), fp);

And if write fails?

> +}
> +
> +void perf_log_addv(const char *fmt, va_list ap)
> +{
> +	char buf[4096];

Add as an optimization add the fp != NULL check here too. Don't need to 
do the vsnprintf only to drop it.

> +
> +	vsnprintf(buf, sizeof(buf), fmt, ap);
> +	perf_log_add(buf);
> +}
>

What limits the size of the file - other than the obvious out of space 
in /tmp? Allow the file to grow without bounds in case a user wants the 
messages seems dangerous.

What about using a circular buffer instead?

David
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