Re: [PATCH v4 0/3] API for exporting connectable file handles to userspace

[Jeff Layton <jlayton@kernel.org>]

On Fri, 2024-10-11 at 11:00 +0200, Amir Goldstein wrote:
> Christian,
> 
> These patches bring the NFS connectable file handles feature to
> userspace servers.
> 
> They rely on your and Aleksa's changes recently merged to v6.12.
> 
> This v4 incorporates the review comments on Jeff and Jan (thanks!)
> and there does not seem to be any objection for this new API, so
> I think it is ready for staging.
> 
> 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 that out-of-tree filesystems return a handle type with upper
> bits set, but AFAIK, no in-tree filesystem does that.
> I added some warnings just in case we encouter that.
> 
> I have written an fstest [4] and a man page draft [5] for the feature.
> 
> Thanks,
> Amir.
> 
> Changes since v3 [3]:
> - Relax WARN_ON in decode and replace with pr_warn in encode (Jeff)
> - Loose the macro FILEID_USER_TYPE_IS_VALID() (Jan)
> - Add explicit check for negative type values (Jan)
> - Added fstest and man-page draft
> 
> 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/
> [3] https://lore.kernel.org/linux-fsdevel/20241008152118.453724-1-amir73il@gmail.com/
> [4] https://github.com/amir73il/xfstests/commits/connectable-fh/
> [5] https://github.com/amir73il/man-pages/commits/connectable-fh/
> 
> 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        | 17 ++++++++-
>  fs/fhandle.c               | 75 +++++++++++++++++++++++++++++++++++---
>  include/linux/exportfs.h   | 13 +++++++
>  include/uapi/linux/fcntl.h |  1 +
>  4 files changed, 98 insertions(+), 8 deletions(-)
> 

Aside from the relatively small stuff I noted in patch #2, this looks
fine to me.

Reviewed-by: Jeff Layton <jlayton@kernel.org>