[PATCH 3/3] selftests: cachestat: test for cachestat availability

[Andre Przywara <andre.przywara@arm.com>]

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

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 the syscall error handling (illegal file descriptor).

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 .../selftests/cachestat/test_cachestat.c      | 22 ++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/cachestat/test_cachestat.c b/tools/testing/selftests/cachestat/test_cachestat.c
index a5a4ac8dcb76c..77620e7ecf562 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 +237,25 @@ 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) {
+		printf("1..0 # Skipped: cachestat syscall not available\n");
+		return KSFT_SKIP;
+	}
+
+	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