selftests/bpf: Test RENAME_EXCHANGE and RENAME_NOREPLACE on bpffs

Add tests to exercise the behaviour of RENAME_EXCHANGE and RENAME_NOREPLACE
on bpffs. The former checks that after an exchange the inode of two
directories has changed. The latter checks that the source still exists
after a failed rename. Generally, having support for renameat2(RENAME_EXCHANGE)
in bpffs fixes atomic upgrades of our sk_lookup control plane.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211028094724.59043-5-lmb@cloudflare.com

tools/testing/selftests/bpf/prog_tests/test_bpffs.c

 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2020 Facebook */
 #define _GNU_SOURCE
+#include <stdio.h>
 #include <sched.h>
 #include <sys/mount.h>
 #include <sys/stat.h>
@@ -29,7 +30,8 @@ static int read_iter(char *file)
 
 static int fn(void)
 {
-	int err;
+	struct stat a, b, c;
+	int err, map;
 
 	err = unshare(CLONE_NEWNS);
 	if (!ASSERT_OK(err, "unshare"))
@@ -67,6 +69,67 @@ static int fn(void)
 	err = read_iter(TDIR "/fs2/progs.debug");
 	if (!ASSERT_OK(err, "reading " TDIR "/fs2/progs.debug"))
 		goto out;
+
+	err = mkdir(TDIR "/fs1/a", 0777);
+	if (!ASSERT_OK(err, "creating " TDIR "/fs1/a"))
+		goto out;
+	err = mkdir(TDIR "/fs1/a/1", 0777);
+	if (!ASSERT_OK(err, "creating " TDIR "/fs1/a/1"))
+		goto out;
+	err = mkdir(TDIR "/fs1/b", 0777);
+	if (!ASSERT_OK(err, "creating " TDIR "/fs1/b"))
+		goto out;
+
+	map = bpf_create_map(BPF_MAP_TYPE_ARRAY, 4, 4, 1, 0);
+	if (!ASSERT_GT(map, 0, "create_map(ARRAY)"))
+		goto out;
+	err = bpf_obj_pin(map, TDIR "/fs1/c");
+	if (!ASSERT_OK(err, "pin map"))
+		goto out;
+	close(map);
+
+	/* Check that RENAME_EXCHANGE works for directories. */
+	err = stat(TDIR "/fs1/a", &a);
+	if (!ASSERT_OK(err, "stat(" TDIR "/fs1/a)"))
+		goto out;
+	err = renameat2(0, TDIR "/fs1/a", 0, TDIR "/fs1/b", RENAME_EXCHANGE);
+	if (!ASSERT_OK(err, "renameat2(/fs1/a, /fs1/b, RENAME_EXCHANGE)"))
+		goto out;
+	err = stat(TDIR "/fs1/b", &b);
+	if (!ASSERT_OK(err, "stat(" TDIR "/fs1/b)"))
+		goto out;
+	if (!ASSERT_EQ(a.st_ino, b.st_ino, "b should have a's inode"))
+		goto out;
+	err = access(TDIR "/fs1/b/1", F_OK);
+	if (!ASSERT_OK(err, "access(" TDIR "/fs1/b/1)"))
+		goto out;
+
+	/* Check that RENAME_EXCHANGE works for mixed file types. */
+	err = stat(TDIR "/fs1/c", &c);
+	if (!ASSERT_OK(err, "stat(" TDIR "/fs1/map)"))
+		goto out;
+	err = renameat2(0, TDIR "/fs1/c", 0, TDIR "/fs1/b", RENAME_EXCHANGE);
+	if (!ASSERT_OK(err, "renameat2(/fs1/c, /fs1/b, RENAME_EXCHANGE)"))
+		goto out;
+	err = stat(TDIR "/fs1/b", &b);
+	if (!ASSERT_OK(err, "stat(" TDIR "/fs1/b)"))
+		goto out;
+	if (!ASSERT_EQ(c.st_ino, b.st_ino, "b should have c's inode"))
+		goto out;
+	err = access(TDIR "/fs1/c/1", F_OK);
+	if (!ASSERT_OK(err, "access(" TDIR "/fs1/c/1)"))
+		goto out;
+
+	/* Check that RENAME_NOREPLACE works. */
+	err = renameat2(0, TDIR "/fs1/b", 0, TDIR "/fs1/a", RENAME_NOREPLACE);
+	if (!ASSERT_ERR(err, "renameat2(RENAME_NOREPLACE)")) {
+		err = -EINVAL;
+		goto out;
+	}
+	err = access(TDIR "/fs1/b", F_OK);
+	if (!ASSERT_OK(err, "access(" TDIR "/fs1/b)"))
+		goto out;
+
 out:
 	umount(TDIR "/fs1");
 	umount(TDIR "/fs2");