[PATCH v3 0/3] API for exporting connectable file handles to userspace

[Amir Goldstein <amir73il@gmail.com>]

Jeff,

These patches bring the NFS connectable file handles feature to
userspace servers.

They rely on Christian's and Aleksa's changes recently merged to v6.12.

The API I chose for encoding conenctable file handles is pretty
conventional (AT_HANDLE_CONNECTABLE).

open_by_handle_at(2) does not have AT_ flags argument, but also, I find
it more useful API that encoding a connectable file handle can mandate
the resolving of a connected fd, without having to opt-in for a
connected fd independently.

I chose to implemnent this by using upper bits in the handle type field
It may be valid (?) for filesystems to return a handle type with upper
bits set, but AFAIK, no in-tree filesystem does that.
I added some assertions just in case.

Thanks,
Amir.

Changes since v2 [2]:
- Use bit arithmetics instead of bitfileds (Jeff)
- Add assertions about use of high type bits

Changes since v1 [1]:
- Assert on encode for disconnected path (Jeff)
- Don't allow AT_HANDLE_CONNECTABLE with AT_EMPTY_PATH
- Drop the O_PATH mount_fd API hack (Jeff)
- Encode an explicit "connectable" flag in handle type

[1] https://lore.kernel.org/linux-fsdevel/20240919140611.1771651-1-amir73il@gmail.com/
[2] https://lore.kernel.org/linux-fsdevel/20240923082829.1910210-1-amir73il@gmail.com/

Amir Goldstein (3):
  fs: prepare for "explicit connectable" file handles
  fs: name_to_handle_at() support for "explicit connectable" file
    handles
  fs: open_by_handle_at() support for decoding "explicit connectable"
    file handles

 fs/exportfs/expfs.c        | 14 ++++++--
 fs/fhandle.c               | 74 ++++++++++++++++++++++++++++++++++----
 include/linux/exportfs.h   | 16 +++++++++
 include/uapi/linux/fcntl.h |  1 +
 4 files changed, 97 insertions(+), 8 deletions(-)

-- 
2.34.1