[PATCH v2 1/2] selftests: cachestat: test for cachestat availability

[Andre Przywara]

As cachestat is a new syscall, it won't be available on older kernels,
for instance those running on a development machine. At the moment the
test reports all tests as "not ok" in this case.

Test for the cachestat syscall availability first, before doing further
tests, and bail out early with a TAP SKIP comment.

This also uses the opportunity to add the proper TAP headers, and add
one check for proper error handling (illegal file descriptor).

Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
Acked-by: Nhat Pham <nphamcs@xxxxxxxxx>
---
 .../selftests/cachestat/test_cachestat.c      | 20 ++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/cachestat/test_cachestat.c b/tools/testing/selftests/cachestat/test_cachestat.c
index a5a4ac8dcb76c..8f8f46c24846d 100644
--- a/tools/testing/selftests/cachestat/test_cachestat.c
+++ b/tools/testing/selftests/cachestat/test_cachestat.c
@@ -15,6 +15,8 @@
 
 #include "../kselftest.h"
 
+#define NR_TESTS	8
+
 static const char * const dev_files[] = {
 	"/dev/zero", "/dev/null", "/dev/urandom",
 	"/proc/version", "/proc"
@@ -235,7 +237,23 @@ bool test_cachestat_shmem(void)
 
 int main(void)
 {
-	int ret = 0;
+	int ret;
+
+	ksft_print_header();
+
+	ret = syscall(__NR_cachestat, -1, NULL, NULL, 0);
+	if (ret == -1 && errno == ENOSYS)
+		ksft_exit_skip("cachestat syscall not available\n");
+
+	ksft_set_plan(NR_TESTS);
+
+	if (ret == -1 && errno == EBADF) {
+		ksft_test_result_pass("bad file descriptor recognized\n");
+		ret = 0;
+	} else {
+		ksft_test_result_fail("bad file descriptor ignored\n");
+		ret = 1;
+	}
 
 	for (int i = 0; i < 5; i++) {
 		const char *dev_filename = dev_files[i];
-- 
2.25.1