tests: skip seccomp_filter_tsync if __NR_seccomp isn't defined

This change does two things to be more defensive: 1. add a checkskip script
which fails if __NR_seccomp isn't defined, and 2. allows
seccomp_filter_tsync to compile even if it isn't defined (and then fails
"gracefully" with a skip message if it does).

The checkskip bits are necessary because zdtm.sh gets confused if the test
exits 0 without actually invoking criu.
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm/live/static/seccomp_filter_tsync.c

@@ -15,7 +15,22 @@
 #include <pthread.h>
 #include "zdtmtst.h"
 
-#define seccomp(_op, _flags, _uargs) syscall(__NR_seccomp, _op, _flags, _uargs)
+#undef __NR_seccomp
+
+#ifdef __NR_seccomp
+#define HAVE_SECCOMP 1
+#else
+#define HAVE_SECCOMP 0
+#define __NR_seccomp -1
+#endif
+
+#ifndef SECCOMP_SET_MODE_FILTER
+#define SECCOMP_SET_MODE_FILTER 1
+#endif
+
+#ifndef SECCOMP_FILTER_FLAG_TSYNC
+#define SECCOMP_FILTER_FLAG_TSYNC 1
+#endif
 
 const char *test_doc	= "Check that SECCOMP_FILTER_FLAG_TSYNC works correctly after restore";
 const char *test_author	= "Tycho Andersen <tycho.andersen@canonical.com>";
@@ -91,6 +106,11 @@ int main(int argc, char ** argv)
 
 	test_init(argc, argv);
 
+	if (!HAVE_SECCOMP) {
+		skip("no seccomp present in this kernel\n");
+		return 0;
+	}
+
 	if (socketpair(PF_LOCAL, SOCK_SEQPACKET, 0, sk_pair)) {
 		pr_perror("socketpair");
 		return -1;

test/zdtm/live/static/seccomp_filter_tsync.checkskip

+#!/bin/bash
+
+set -e
+
+cat > /tmp/has_nr_seccomp.c <<EOF
+#include <syscall.h>
+int main() {
+	return __NR_seccomp;
+}
+EOF
+
+make /tmp/has_nr_seccomp