The NFSv4.1 protocol adds support for directory delegations, but it
specifies that if you already have a delegation and try to request a new
one on the same filehandle, the server must reply that the delegation is
unavailable.

Add a new lease_manager callback to allow the lease manager (nfsd in
this case) to impose extra checks when performing a setlease.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/locks.c               |  5 +++++
 include/linux/filelock.h | 10 ++++++++++
 2 files changed, 15 insertions(+)

diff --git a/fs/locks.c b/fs/locks.c
index cb4b35d26162..415cca8e9565 100644
--- a/fs/locks.c
+++ b/fs/locks.c

@@ -1822,6 +1822,11 @@ generic_add_lease(struct file *filp, int arg, struct file_lease **flp, void **pr
 			continue;
 		}
 
+		/* Allow the lease manager to veto the setlease */
+		if (lease->fl_lmops->lm_set_conflict &&
+		    lease->fl_lmops->lm_set_conflict(lease, fl))
+			goto out;
+
 		/*
 		 * No exclusive leases if someone else has a lease on
 		 * this file:

diff --git a/include/linux/filelock.h b/include/linux/filelock.h
index daee999d05f3..c5fc768087df 100644
--- a/include/linux/filelock.h
+++ b/include/linux/filelock.h

@@ -49,6 +49,16 @@ struct lease_manager_operations {
 	int (*lm_change)(struct file_lease *, int, struct list_head *);
 	void (*lm_setup)(struct file_lease *, void **);
 	bool (*lm_breaker_owns_lease)(struct file_lease *);
+
+	/**
+	 * lm_set_conflict - extra conditions for setlease
+	 * @new: new file_lease being set
+	 * @old: old (extant) file_lease
+	 *
+	 * This allows the lease manager to add extra conditions when
+	 * setting a lease.