[PATCH v3 2/4] userfaultfd: selftest: Skip test if userfaultfd() syscall not supported

[Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx>]

Since there's no point in doing anything in this case, immediately exit the
process.

And take the opportunity to improve the error message.

Before:

  # ./userfaultfd shmem 10 10
  nr_pages: 160, nr_pages_per_cpu: 40
  userfaultfd syscall not available in this kernel
  # echo $?
  1

After:

  # ./userfaultfd shmem 10 10
  nr_pages: 160, nr_pages_per_cpu: 40
  userfaultfd syscall not available in this kernel: Function not implemented
  # echo $?
  4

Suggested-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx>
Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
---
 tools/testing/selftests/vm/userfaultfd.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index e4099afe7557..d728bd1cb33c 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c
@@ -636,9 +636,11 @@ static int userfaultfd_open(int features)
 
 	uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
 	if (uffd < 0) {
-		fprintf(stderr,
-			"userfaultfd syscall not available in this kernel\n");
-		return 1;
+		int errnum = errno;
+
+		perror("userfaultfd syscall not available in this kernel");
+
+		exit(errnum == ENOSYS ? KSFT_SKIP : 1);
 	}
 	uffd_flags = fcntl(uffd, F_GETFD, NULL);