selftests: pidfd: skip test on kcmp() ENOSYS

Skip test if kcmp() is not available, for example if kernel is compiled
without CONFIG_CHECKPOINT_RESTORE=y.

Signed-off-by: Tommi Rantala <[e-mail]>
Acked-by: Christian Brauner <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/pidfd/pidfd_getfd_test.c

···
 	fd = sys_pidfd_getfd(self->pidfd, self->remote_fd, 0);
 	ASSERT_GE(fd, 0);
 
-	EXPECT_EQ(0, sys_kcmp(getpid(), self->pid, KCMP_FILE, fd, self->remote_fd));
+	ret = sys_kcmp(getpid(), self->pid, KCMP_FILE, fd, self->remote_fd);
+	if (ret < 0 && errno == ENOSYS)
+		SKIP(return, "kcmp() syscall not supported");
+	EXPECT_EQ(ret, 0);
 
 	ret = fcntl(fd, F_GETFD);
 	ASSERT_GE(ret, 0);