perf tools: Allow to reset open files counter

I hit a bug when running test suite without forking
each test (-F option):

  $ perf test -F dso
   8: Test dso data read                                       : Ok
   9: Test dso data cache                                      : FAILED!
  10: Test dso data reopen                                     : FAILED!

The reason the session file limit is set just once for
perf process so we need to reset it for each test,
otherwise wrong limit is taken into account.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Nilay Vaish <nilayvaish@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1467113345-12669-2-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/dso-data.c

@@ -251,6 +251,9 @@ int test__dso_data_cache(int subtest __maybe_unused)
 	long nr_end, nr = open_files_cnt();
 	int dso_cnt, limit, i, fd;
 
+	/* Rest the internal dso open counter limit. */
+	reset_fd_limit();
+
 	memset(&machine, 0, sizeof(machine));
 
 	/* set as system limit */
@@ -312,6 +315,9 @@ int test__dso_data_reopen(int subtest __maybe_unused)
 #define dso_1 (dsos[1])
 #define dso_2 (dsos[2])
 
+	/* Rest the internal dso open counter limit. */
+	reset_fd_limit();
+
 	memset(&machine, 0, sizeof(machine));
 
 	/*

tools/perf/util/dso.c

@@ -442,17 +442,27 @@ static rlim_t get_fd_limit(void)
 	return limit;
 }
 
+static rlim_t fd_limit;
+
+/*
+ * Used only by tests/dso-data.c to reset the environment
+ * for tests. I dont expect we should change this during
+ * standard runtime.
+ */
+void reset_fd_limit(void)
+{
+	fd_limit = 0;
+}
+
 static bool may_cache_fd(void)
 {
-	static rlim_t limit;
+	if (!fd_limit)
+		fd_limit = get_fd_limit();
 
-	if (!limit)
-		limit = get_fd_limit();
-
-	if (limit == RLIM_INFINITY)
+	if (fd_limit == RLIM_INFINITY)
 		return true;
 
-	return limit > (rlim_t) dso__data_open_cnt;
+	return fd_limit > (rlim_t) dso__data_open_cnt;
 }
 
 /*

tools/perf/util/dso.h

@@ -360,4 +360,6 @@ enum dso_type dso__type(struct dso *dso, struct machine *machine);
 
 int dso__strerror_load(struct dso *dso, char *buf, size_t buflen);
 
+void reset_fd_limit(void);
+
 #endif /* __PERF_DSO */