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SubjectRe: [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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