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.

Signed-off-by: Lorenz Bauer <redacted>
---
 .../selftests/bpf/prog_tests/test_bpffs.c     | 39 +++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/test_bpffs.c b/tools/testing/selftests/bpf/prog_tests/test_bpffs.c
index 172c999e523c..9c28ae9589bf 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_bpffs.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_bpffs.c

@@ -1,6 +1,7 @@
 // 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>

@@ -29,6 +30,7 @@ static int read_iter(char *file)

 static int fn(void)
 {
+       struct stat a, b;
        int err, duration = 0;

        err = unshare(CLONE_NEWNS);

@@ -67,6 +69,43 @@ static int fn(void)
        err = read_iter(TDIR "/fs2/progs.debug");
        if (CHECK(err, "reading " TDIR "/fs2/progs.debug", "failed\n"))
                goto out;
+
+       err = mkdir(TDIR "/fs1/a", 0777);
+       if (CHECK(err, "creating " TDIR "/fs1/a", "failed\n"))
+               goto out;
+       err = mkdir(TDIR "/fs1/a/1", 0777);
+       if (CHECK(err, "creating " TDIR "/fs1/a/1", "failed\n"))
+               goto out;
+       err = mkdir(TDIR "/fs1/b", 0777);
+       if (CHECK(err, "creating " TDIR "/fs1/b", "failed\n"))
+               goto out;
+
+       /* Check that RENAME_EXCHANGE works. */
+       err = stat(TDIR "/fs1/a", &a);
+       if (CHECK(err, "stat(" TDIR "/fs1/a)", "failed\n"))
+               goto out;
+       err = renameat2(0, TDIR "/fs1/a", 0, TDIR "/fs1/b", RENAME_EXCHANGE);
+       if (CHECK(err, "renameat2(RENAME_EXCHANGE)", "failed\n"))
+               goto out;
+       err = stat(TDIR "/fs1/b", &b);
+       if (CHECK(err, "stat(" TDIR "/fs1/b)", "failed\n"))
+               goto out;
+       if (CHECK(a.st_ino != b.st_ino, "b should have a's inode", "failed\n"))
+               goto out;
+       err = access(TDIR "/fs1/b/1", F_OK);
+       if (CHECK(err, "access(" TDIR "/fs1/b/1)", "failed\n"))
+               goto out;
+
+       /* Check that RENAME_NOREPLACE works. */
+       err = renameat2(0, TDIR "/fs1/b", 0, TDIR "/fs1/a", RENAME_NOREPLACE);
+       if (CHECK(!err, "renameat2(RENAME_NOREPLACE)", "succeeded\n")) {
+               err = -EINVAL;
+               goto out;
+       }
+       err = access(TDIR "/fs1/b", F_OK);
+       if (CHECK(err, "access(" TDIR "/fs1/b)", "failed\n"))
+               goto out;
+