This series implements the mkdirat2() syscall that was suggested over
at the UAPI group kernel feature page [1] with some tests.

Obviously, we probably also want to implement equivalent mknodeat2() and
symlinkat2() syscalls, but their implementation can be done quite similar
I believe.

This has been compiled and tested on x86 only.

[1]: https://github.com/uapi-group/kernel-features?tab=readme-ov-file#race-free-creation-and-opening-of-non-file-inodes

v2:
- Use AT_* flags.
- Ensure an fd is allocated only if mkdir and open_dentry succeed.
- The returned fd gets O_CLOEXEC by default.
- Renamed syscall from mkdirat_fd() to mkdirat2().

Jori Koolstra (2):
  vfs: syscalls: add mkdirat2() that returns an O_DIRECTORY fd
  selftest: add tests for mkdirat2()

 arch/x86/entry/syscalls/syscall_64.tbl        |   1 +
 fs/internal.h                                 |   2 +
 fs/namei.c                                    |  44 +++++-
 include/linux/syscalls.h                      |   2 +
 include/uapi/asm-generic/unistd.h             |   5 +-
 scripts/syscall.tbl                           |   1 +
 tools/include/uapi/asm-generic/unistd.h       |   5 +-
 .../testing/selftests/filesystems/.gitignore  |   1 +
 tools/testing/selftests/filesystems/Makefile  |   4 +-
 .../selftests/filesystems/mkdirat_fd_test.c   | 143 ++++++++++++++++++
 10 files changed, 200 insertions(+), 8 deletions(-)
 create mode 100644 tools/testing/selftests/filesystems/mkdirat_fd_test.c

-- 
2.53.0