[PATCH v3 0/3] fuse: Expose more information of fuse backing files to userspace

[Chen Linxuan via B4 Relay <devnull+chenlinxuan.uniontech.com@kernel.org>]

Please review this patch series carefully. I am new to kernel
development and I am not quite sure if I have followed the best
practices, especially in terms of seq_file, error handling and locking.
I would appreciate any feedback.

I have do some simply testing using libfuse example [1]. It seems to
work well.

[1]: https://github.com/libfuse/libfuse/blob/master/example/passthrough_hp.cc

Signed-off-by: Chen Linxuan <chenlinxuan@uniontech.com>
---
Changes in v3:
- Apply some suggestions from Amir Goldstein
- Link to v2: https://lore.kernel.org/r/20250508-fusectl-backing-files-v2-0-62f564e76984@uniontech.com

Changes in v2:
- Void using seq_file private field as it seems that we can just simply
  returning fuse_backing_files_seq_state in start() and next()
- Apply some suggestions from Amir Goldstein:
  - Use idr_get_next() for iteration
  - Do fuse_backing_get/put(fb) around dereferencing fb->file
- Update fdinfo of fuse files
- Link to v1: https://lore.kernel.org/r/20250507032926.377076-2-chenlinxuan@uniontech.com

---
Chen Linxuan (3):
      fs: fuse: add const qualifier to fuse_ctl_file_conn_get()
      fs: fuse: add backing_files control file
      fs: fuse: add more information to fdinfo

 fs/fuse/control.c | 157 +++++++++++++++++++++++++++++++++++++++++++++++++-----
 fs/fuse/file.c    |  20 +++++++
 fs/fuse/fuse_i.h  |   2 +-
 3 files changed, 165 insertions(+), 14 deletions(-)
---
base-commit: d76bb1ebb5587f66b0f8b8099bfbb44722bc08b3
change-id: 20250508-fusectl-backing-files-6810d290e798

Best regards,
-- 
Chen Linxuan <chenlinxuan@uniontech.com>