Merge tag 'ovl-vfs-6.8' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/overlay...

Pull backing file updates from Amir Goldstein:

These patches essentially just lift some overlayfs code to common code.
The motivation is to reuse common stacking code for the FUSE passthrough
patches that I am shaping up for upstream. The FUSE passthrough work
will be coming in over the next cycles.

I have been testing those patches with my fuse-backing-fd development
branch for quite some time and I think both you and Miklos gave a
conceptual ACK to some version of this work.

* tag 'ovl-vfs-6.8' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/overlayfs/vfs:
  fs: factor out backing_file_mmap() helper
  fs: factor out backing_file_splice_{read,write}() helpers
  fs: factor out backing_file_{read,write}_iter() helpers
  fs: prepare for stackable filesystems backing file helpers

Signed-off-by: Christian Brauner <brauner@kernel.org>