selftests/landlock: Make tests build with old libc

Replace SYS_<syscall> with __NR_<syscall>.  Using the __NR_<syscall>
notation, provided by UAPI, is useful to build tests on systems without
the SYS_<syscall> definitions.

Replace SYS_pivot_root with __NR_pivot_root, and SYS_move_mount with
__NR_move_mount.

Define renameat2() and RENAME_EXCHANGE if they are unknown to old build
systems.

Cc: Shuah Khan <shuah@kernel.org>
Link: https://lore.kernel.org/r/20220506160820.524344-3-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>

tools/testing/selftests/landlock/fs_test.c

@@ -22,6 +22,19 @@
 
 #include "common.h"
 
+#ifndef renameat2
+int renameat2(int olddirfd, const char *oldpath, int newdirfd,
+	      const char *newpath, unsigned int flags)
+{
+	return syscall(__NR_renameat2, olddirfd, oldpath, newdirfd, newpath,
+		       flags);
+}
+#endif
+
+#ifndef RENAME_EXCHANGE
+#define RENAME_EXCHANGE (1 << 1)
+#endif
+
 #define TMP_DIR "tmp"
 #define BINARY_PATH "./true"
 
@@ -1279,7 +1292,7 @@ TEST_F_FORK(layout1, rule_inside_mount_ns)
 	int ruleset_fd;
 
 	set_cap(_metadata, CAP_SYS_ADMIN);
-	ASSERT_EQ(0, syscall(SYS_pivot_root, dir_s3d2, dir_s3d3))
+	ASSERT_EQ(0, syscall(__NR_pivot_root, dir_s3d2, dir_s3d3))
 	{
 		TH_LOG("Failed to pivot root: %s", strerror(errno));
 	};
@@ -1313,7 +1326,7 @@ TEST_F_FORK(layout1, mount_and_pivot)
 	set_cap(_metadata, CAP_SYS_ADMIN);
 	ASSERT_EQ(-1, mount(NULL, dir_s3d2, NULL, MS_RDONLY, NULL));
 	ASSERT_EQ(EPERM, errno);
-	ASSERT_EQ(-1, syscall(SYS_pivot_root, dir_s3d2, dir_s3d3));
+	ASSERT_EQ(-1, syscall(__NR_pivot_root, dir_s3d2, dir_s3d3));
 	ASSERT_EQ(EPERM, errno);
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 }
@@ -1332,13 +1345,13 @@ TEST_F_FORK(layout1, move_mount)
 	ASSERT_LE(0, ruleset_fd);
 
 	set_cap(_metadata, CAP_SYS_ADMIN);
-	ASSERT_EQ(0, syscall(SYS_move_mount, AT_FDCWD, dir_s3d2, AT_FDCWD,
+	ASSERT_EQ(0, syscall(__NR_move_mount, AT_FDCWD, dir_s3d2, AT_FDCWD,
 			     dir_s1d2, 0))
 	{
 		TH_LOG("Failed to move mount: %s", strerror(errno));
 	}
 
-	ASSERT_EQ(0, syscall(SYS_move_mount, AT_FDCWD, dir_s1d2, AT_FDCWD,
+	ASSERT_EQ(0, syscall(__NR_move_mount, AT_FDCWD, dir_s1d2, AT_FDCWD,
 			     dir_s3d2, 0));
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 
@@ -1346,7 +1359,7 @@ TEST_F_FORK(layout1, move_mount)
 	ASSERT_EQ(0, close(ruleset_fd));
 
 	set_cap(_metadata, CAP_SYS_ADMIN);
-	ASSERT_EQ(-1, syscall(SYS_move_mount, AT_FDCWD, dir_s3d2, AT_FDCWD,
+	ASSERT_EQ(-1, syscall(__NR_move_mount, AT_FDCWD, dir_s3d2, AT_FDCWD,
 			      dir_s1d2, 0));
 	ASSERT_EQ(EPERM, errno);
 	clear_cap(_metadata, CAP_SYS_ADMIN);