vfs: add O_CREAT|O_DIRECTORY to open*(2)

This series implements new semantics for the O_CREAT|O_DIRECTORY flag
combination for open*(2): perform a mkdir and open the resulting
directory; return a pinning fd (which mkdir does not).

Most of the work happens in "vfs: add O_CREAT|O_DIRECTORY to open*(2),"
as may be expected. Before that there is some clean-up work and
preparation. Also, the inconsistency in calling audit_inode_child() in
lookup_open() versus vfs_create() path is addressed. The
"vfs: short-circuit MAY_WRITE access for O_DIRECTORY opens" patch is
also worth paying extra attention to as it short-circuits doomed opening
of directories as writable. This check for regular files is now done
very late in do_open(), but for O_CREAT|O_DIRECTORY this is unacceptable
as this would create the directory and then still fail.

Jori Koolstra (14):
  fs/namei.c: use trailing_slashes()
  vfs: move create error && negative dentry case in lookup_open() up
  vfs: prepare vfs_creat|mkdir_no_perm for reuse in lookup_open()
  vfs: call audit_inode_child() in lookup_open() on failure too
  fs/namei.c: update docstring of atomic_open()
  vfs: lookup_open(): move setting FMODE_CREATED down
  vfs: move ->create check in lookup_open() to before try_break_deleg()
  vfs: lookup_open(): use vfs_create_no_perm()
  vfs: add O_CREAT|O_DIRECTORY to open*(2)
  vfs: move O_IS_MKDIR check from lookup_open() into individual
    filesystems
  vfs: refuse O_CREAT for directories through a dangling symlink
  vfs: short-circuit MAY_WRITE access for O_DIRECTORY opens
  selftest: fix headers in fclog.c
  selftest: add tests for open*(O_CREAT|O_DIRECTORY)

 fs/9p/vfs_inode.c                             |   3 +
 fs/9p/vfs_inode_dotl.c                        |   3 +
 fs/ceph/file.c                                |   3 +
 fs/fuse/dir.c                                 |   3 +
 fs/gfs2/inode.c                               |   3 +
 fs/namei.c                                    | 313 ++++++++++++------
 fs/nfs/dir.c                                  |   6 +
 fs/open.c                                     |  32 +-
 fs/smb/client/dir.c                           |   3 +
 fs/vboxsf/dir.c                               |   3 +
 include/linux/fcntl.h                         |   6 +
 .../testing/selftests/filesystems/.gitignore  |   1 +
 tools/testing/selftests/filesystems/Makefile  |   2 +-
 tools/testing/selftests/filesystems/fclog.c   |   4 +-
 .../filesystems/open_o_creat_o_dir.c          | 197 +++++++++++
 15 files changed, 463 insertions(+), 119 deletions(-)
 create mode 100644 tools/testing/selftests/filesystems/open_o_creat_o_dir.c

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2.55.0