[PATCH v1 1/2] perf tools: shortcut PERF_FLAG_FD_CLOEXEC probing in case of EBUSY error

[Yann Droneaud <ydroneaud@opteya.com>]

This patch is a simplification of the logic introduced as part of
commit 63914aca8f7e ("perf tools: Show better error message in case
we fail to open counters due to EBUSY error"): if -EBUSY is reported
by perf_event_open(), it will not be possible to probe
PERF_FLAG_FD_CLOEXEC, so it's safe to leave early.

It should be noted that -EBUSY errors are not really expected here
since commit 038fa0b9739d ("perf tools: Fix PERF_FLAG_FD_CLOEXEC
flag probing event type open counters due to EBUSY error"):
the perf event type used now should be safe to use regarding -EBUSY
error.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: William Cohen <wcohen@redhat.com>
Link: http://lkml.kernel.org/r/cover.1425901229.git.ydroneaud@opteya.com
Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
---
 tools/perf/util/cloexec.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/cloexec.c b/tools/perf/util/cloexec.c
index 6da965bdbc2c..2f05f8f8c22e 100644
--- a/tools/perf/util/cloexec.c
+++ b/tools/perf/util/cloexec.c
@@ -46,7 +46,11 @@ static int perf_flag_probe(void)
 		return 1;
 	}
 
-	WARN_ONCE(err != EINVAL && err != EBUSY,
+	/* ignore busy errors */
+	if (err == EBUSY)
+		return -1;
+
+	WARN_ONCE(err != EINVAL,
 		  "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
 		  err, strerror_r(err, sbuf, sizeof(sbuf)));
 
@@ -64,7 +68,7 @@ static int perf_flag_probe(void)
 	if (fd >= 0)
 		close(fd);
 
-	if (WARN_ONCE(fd < 0 && err != EBUSY,
+	if (WARN_ONCE(fd < 0,
 		      "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
 		      err, strerror_r(err, sbuf, sizeof(sbuf))))
 		return -1;
-- 
2.1.0