[PATCH 0/4] exportfs: add flag to allow marking export operations as only supporting file handles

[Christian Brauner <brauner@kernel.org>]

Hey,

Some filesystems like kernfs and pidfs support file handles as a
convenience to enable the use of name_to_handle_at(2) and
open_by_handle_at(2) but don't want to and cannot be reliably exported.
Add a flag that allows them to mark their export operations accordingly
and make NFS check for its presence.

@Amir, I'll reorder the patches such that this series comes prior to the
pidfs file handle series. Doing it that way will mean that there's never
a state where pidfs supports file handles while also being exportable.
It's probably not a big deal but it's definitely cleaner. It also means
the last patch in this series to mark pidfs as non-exportable can be
dropped. Instead pidfs export operations will be marked as
non-exportable in the patch that they are added in.

Thanks!
Christian

---
Christian Brauner (4):
      exportfs: add flag to indicate local file handles
      kernfs: restrict to local file handles
      ovl: restrict to exportable file handles
      pidfs: restrict to local file handles

 fs/kernfs/mount.c        | 1 +
 fs/nfsd/export.c         | 8 +++++++-
 fs/overlayfs/util.c      | 7 ++++++-
 fs/pidfs.c               | 1 +
 include/linux/exportfs.h | 1 +
 5 files changed, 16 insertions(+), 2 deletions(-)
---
base-commit: 74e20c5946ab3f8ad959ea34f63f21e157d3ebae
change-id: 20241201-work-exportfs-cd49bee773c5