[PATCH v7 4/5] linux: Add tst-mount to check for Linux new mount API

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

The new mount API was added on Linux 5.2 with six new syscalls:
fsopen, fsconfig, fsmount, move_mount, fspick, and open_tree.

The new test verifies minimal functionality along with error paths
for specific arguments and their corner cases.

Checked on x86_64-linux-gnu.
---
 sysdeps/unix/sysv/linux/Makefile    |  1 +
 sysdeps/unix/sysv/linux/tst-mount.c | 95 +++++++++++++++++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 sysdeps/unix/sysv/linux/tst-mount.c

diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 7ffcf7ed83..2ccc92b6b8 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -130,6 +130,7 @@ tests += tst-clone tst-clone2 tst-clone3 tst-fanotify tst-personality \
   tst-getauxval \
   tst-pidfd \
   tst-process_mrelease \
+  tst-mount \
   # tests
 
 # process_madvise requires CAP_SYS_ADMIN.
diff --git a/sysdeps/unix/sysv/linux/tst-mount.c b/sysdeps/unix/sysv/linux/tst-mount.c
new file mode 100644
index 0000000000..12a665f950
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-mount.c
@@ -0,0 +1,95 @@
+/* Basic tests for the new Linux API added on Linux 5.2.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If
+   not, see <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <support/check.h>
+#include <support/xunistd.h>
+#include <support/namespace.h>
+#include <sys/wait.h>
+#include <sys/mount.h>
+
+static void
+subprocess (void)
+{
+  int r = fsopen ("it_should_be_not_a_valid_mount", 0);
+  TEST_VERIFY_EXIT (r == -1);
+  if (errno == ENOSYS)
+    FAIL_UNSUPPORTED ("kernel does not support new mount API, skipping test");
+  TEST_COMPARE (errno, ENODEV);
+
+  int fd = fsopen ("tmpfs", FSOPEN_CLOEXEC);
+  TEST_VERIFY (fd != -1);
+
+  TEST_COMPARE (fsconfig (-1, FSCONFIG_SET_STRING, "size", "2048", 0), -1);
+  TEST_COMPARE (errno, EINVAL);
+
+  {
+    int r = fsconfig (fd, FSCONFIG_SET_STRING, "size", "2048", 0);
+    TEST_VERIFY (r != -1);
+    r = fsconfig (fd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
+    TEST_VERIFY (r != -1);
+  }
+
+  TEST_COMPARE (fsmount (-1, FSMOUNT_CLOEXEC, MOUNT_ATTR_NODEV), -1);
+  TEST_COMPARE (errno, EBADF);
+
+  int mfd = fsmount (fd, FSMOUNT_CLOEXEC, MOUNT_ATTR_NODEV);
+  TEST_VERIFY (mfd != -1);
+
+  TEST_COMPARE (move_mount (-1, "", AT_FDCWD, "/tmp", 0), -1);
+  TEST_COMPARE (errno, ENOENT);
+  {
+    int r = move_mount (mfd, "", AT_FDCWD, "/tmp", MOVE_MOUNT_F_EMPTY_PATH);
+    TEST_VERIFY (r != -1);
+  }
+
+  TEST_COMPARE (fspick (AT_FDCWD, "", 0), -1);
+  TEST_COMPARE (errno, ENOENT);
+  {
+    int pfd = fspick (AT_FDCWD, "/tmp", FSPICK_CLOEXEC);
+    TEST_VERIFY (pfd != -1);
+  }
+
+  TEST_COMPARE (open_tree (AT_FDCWD, "", 0), -1);
+  TEST_COMPARE (errno, ENOENT);
+  {
+    int fd_tree = open_tree (AT_FDCWD, "/tmp",
+			     OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
+    TEST_VERIFY (fd_tree != -1);
+  }
+
+  _exit (0);
+}
+
+static int
+do_test (void)
+{
+  support_become_root ();
+
+  pid_t pid = xfork ();
+  if (pid == 0)
+    subprocess ();
+
+  int status;
+  xwaitpid (pid, &status, 0);
+  TEST_VERIFY (WIFEXITED (status));
+
+  return 0;
+}
+
+#include <support/test-driver.c>
-- 
2.34.1