[PATCH] perf stat: fix default output file

[PATCH] perf stat: fix default output file

[Stephane Eranian]

The following commit:

commit 56f3bae70638b33477a6015fd362ccfe354fd3ee
Author: Jim Cromie <jim.cromie@gmail.com>
Date:   Wed Sep 7 17:14:00 2011 -0600

    perf stat: Add --log-fd <N> option to redirect stderr elsewhere

introduced a bug in the way perf stat outputs the results by default, i.e.,
without the --log-fd or --output option. It would default to writing to
file descriptor 0, i.e., stdin. Writing to stdin is allowed and is equivalent
to writing to stdout. However, there is a major difference for any script that
was already capturing the output of perf stat via redirection:

    perf stat >/tmp/log .... or perf stat 2>/tmp/log ....

They would not capture anything anymore. They would have to do:
    perf stat 0>/tmp/log ...

This breaks compatibility with existing scripts and does not look very
natural.

This patch fixes the problem by looking at output_fd only when it
was modified by user (> 0). It also checks that the value if positive.
Passing --log-fd 0 is ignored.

I would also argue that defaulting to stderr for the results is not
the right thing to do, though this patch does not address this specific
issue.

Signed-off-by: Stephane Eranian <eranian@google.com>
---

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 36603e4..56e6040 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -1179,6 +1179,12 @@ int cmd_stat(int argc, const char **argv, const char *prefix __used)
 		fprintf(stderr, "cannot use both --output and --log-fd\n");
 		usage_with_options(stat_usage, options);
 	}
+
+	if (output_fd < 0) {
+		fprintf(stderr, "argument to --log-fd must be a > 0\n");
+		usage_with_options(stat_usage, options);
+	}
+
 	if (!output) {
 		struct timespec tm;
 		mode = append_file ? "a" : "w";
@@ -1190,7 +1196,7 @@ int cmd_stat(int argc, const char **argv, const char *prefix __used)
 		}
 		clock_gettime(CLOCK_REALTIME, &tm);
 		fprintf(output, "# started on %s\n", ctime(&tm.tv_sec));
-	} else if (output_fd != 2) {
+	} else if (output_fd > 0) {
 		mode = append_file ? "a" : "w";
 		output = fdopen(output_fd, mode);
 		if (!output) {

Re: [PATCH] perf stat: fix default output file

[Stephane Eranian]

Ping?

On Tue, May 15, 2012 at 1:11 PM, Stephane Eranian <eranian@google.com> wrote:
>
> The following commit:
>
> commit 56f3bae70638b33477a6015fd362ccfe354fd3ee
> Author: Jim Cromie <jim.cromie@gmail.com>
> Date:   Wed Sep 7 17:14:00 2011 -0600
>
>    perf stat: Add --log-fd <N> option to redirect stderr elsewhere
>
> introduced a bug in the way perf stat outputs the results by default, i.e.,
> without the --log-fd or --output option. It would default to writing to
> file descriptor 0, i.e., stdin. Writing to stdin is allowed and is equivalent
> to writing to stdout. However, there is a major difference for any script that
> was already capturing the output of perf stat via redirection:
>
>    perf stat >/tmp/log .... or perf stat 2>/tmp/log ....
>
> They would not capture anything anymore. They would have to do:
>    perf stat 0>/tmp/log ...
>
> This breaks compatibility with existing scripts and does not look very
> natural.
>
> This patch fixes the problem by looking at output_fd only when it
> was modified by user (> 0). It also checks that the value if positive.
> Passing --log-fd 0 is ignored.
>
> I would also argue that defaulting to stderr for the results is not
> the right thing to do, though this patch does not address this specific
> issue.
>
> Signed-off-by: Stephane Eranian <eranian@google.com>
> ---
>
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 36603e4..56e6040 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -1179,6 +1179,12 @@ int cmd_stat(int argc, const char **argv, const char *prefix __used)
>                fprintf(stderr, "cannot use both --output and --log-fd\n");
>                usage_with_options(stat_usage, options);
>        }
> +
> +       if (output_fd < 0) {
> +               fprintf(stderr, "argument to --log-fd must be a > 0\n");
> +               usage_with_options(stat_usage, options);
> +       }
> +
>        if (!output) {
>                struct timespec tm;
>                mode = append_file ? "a" : "w";
> @@ -1190,7 +1196,7 @@ int cmd_stat(int argc, const char **argv, const char *prefix __used)
>                }
>                clock_gettime(CLOCK_REALTIME, &tm);
>                fprintf(output, "# started on %s\n", ctime(&tm.tv_sec));
> -       } else if (output_fd != 2) {
> +       } else if (output_fd > 0) {
>                mode = append_file ? "a" : "w";
>                output = fdopen(output_fd, mode);
>                if (!output) {

[tip:perf/urgent] perf stat: Fix default output file

[tip-bot for Stephane Eranian]

Commit-ID:  fc3e4d077d5c7a7bc1ad5bc143895b4e070e5a8b
Gitweb:     http://git.kernel.org/tip/fc3e4d077d5c7a7bc1ad5bc143895b4e070e5a8b
Author:     Stephane Eranian <eranian@google.com>
AuthorDate: Tue, 15 May 2012 13:11:11 +0200
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Mon, 11 Jun 2012 11:20:21 -0300

perf stat: Fix default output file

The following commit:

commit 56f3bae70638b33477a6015fd362ccfe354fd3ee
Author: Jim Cromie <jim.cromie@gmail.com>
Date:   Wed Sep 7 17:14:00 2011 -0600

    perf stat: Add --log-fd <N> option to redirect stderr elsewhere

introduced a bug in the way perf stat outputs the results by default,
i.e., without the --log-fd or --output option. It would default to
writing to file descriptor 0, i.e., stdin. Writing to stdin is allowed
and is equivalent to writing to stdout. However, there is a major
difference for any script that was already capturing the output of perf
stat via redirection:

    perf stat >/tmp/log .... or perf stat 2>/tmp/log ....

They would not capture anything anymore. They would have to do:
    perf stat 0>/tmp/log ...

This breaks compatibility with existing scripts and does not look very
natural.

This patch fixes the problem by looking at output_fd only when it was
modified by user (> 0). It also checks that the value if positive.
Passing --log-fd 0 is ignored.

I would also argue that defaulting to stderr for the results is not the
right thing to do, though this patch does not address this specific
issue.

Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jim Cromie <jim.cromie@gmail.com>
Link: http://lkml.kernel.org/r/20120515111111.GA9870@quad
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/builtin-stat.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 2625899..07b5c77 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -1179,6 +1179,12 @@ int cmd_stat(int argc, const char **argv, const char *prefix __used)
 		fprintf(stderr, "cannot use both --output and --log-fd\n");
 		usage_with_options(stat_usage, options);
 	}
+
+	if (output_fd < 0) {
+		fprintf(stderr, "argument to --log-fd must be a > 0\n");
+		usage_with_options(stat_usage, options);
+	}
+
 	if (!output) {
 		struct timespec tm;
 		mode = append_file ? "a" : "w";
@@ -1190,7 +1196,7 @@ int cmd_stat(int argc, const char **argv, const char *prefix __used)
 		}
 		clock_gettime(CLOCK_REALTIME, &tm);
 		fprintf(output, "# started on %s\n", ctime(&tm.tv_sec));
-	} else if (output_fd != 2) {
+	} else if (output_fd > 0) {
 		mode = append_file ? "a" : "w";
 		output = fdopen(output_fd, mode);
 		if (!output) {