nfsd: Ensure knfsd shuts down when the "nfsd" pseudofs is unmounted

In order to ensure that knfsd threads don't linger once the nfsd
pseudofs is unmounted (e.g. when the container is killed) we let
nfsd_umount() shut down those threads and wait for them to exit.

This also should ensure that we don't need to do a kernel mount of
the pseudofs, since the thread lifetime is now limited by the
lifetime of the filesystem.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
index 8bdc37a..27c1308 100644
--- a/fs/nfsd/nfsd.h
+++ b/fs/nfsd/nfsd.h
@@ -93,13 +93,12 @@ int		nfsd_get_nrthreads(int n, int *, struct net *);
 int		nfsd_set_nrthreads(int n, int *, struct net *);
 int		nfsd_pool_stats_open(struct inode *, struct file *);
 int		nfsd_pool_stats_release(struct inode *, struct file *);
+void		nfsd_shutdown_threads(struct net *net);
 
 void		nfsd_destroy(struct net *net);
 
 bool		i_am_nfsd(void);
 
-int get_nfsdfs(struct net *);
-
 struct nfsdfs_client {
 	struct kref cl_ref;
 	void (*cl_release)(struct kref *kref);