From fc3e4d077d5c7a7bc1ad5bc143895b4e070e5a8b Mon Sep 17 00:00:00 2001 From: Stephane Eranian Date: Tue, 15 May 2012 13:11:11 +0200 Subject: [PATCH] perf stat: Fix default output file The following commit: commit 56f3bae70638b33477a6015fd362ccfe354fd3ee Author: Jim Cromie Date: Wed Sep 7 17:14:00 2011 -0600 perf stat: Add --log-fd 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 Cc: David Ahern Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Jim Cromie Link: http://lkml.kernel.org/r/20120515111111.GA9870@quad Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/builtin-stat.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c index 262589991ea4..07b5c7703dd1 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) {