On Wed, Jul 28, 2021 at 08:37:45AM +1000, NeilBrown wrote:

In order to support filehandle lookup in filesystems with internal
mounts (multiple subvols in the one filesystem) reconnect_path() in
exportfs will need to find out if a given dentry is already mounted.
This can be done with the function lookup_mnt(), so export that to make
it available.

IMO having exportfs modular is wrong - note that fs/fhandle.c is
	* calling functions in exportfs
	* non-modular
	* ... and not going to be modular, no matter what - there
are syscalls in it.