On Tue, 2025-10-14 at 16:34 +1100, NeilBrown wrote:

On Tue, 14 Oct 2025, Jeff Layton wrote:

quoted

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 this extra check when performing a setlease.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/locks.c               |  5 +++++
 include/linux/filelock.h | 14 ++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/fs/locks.c b/fs/locks.c
index 0b16921fb52e602ea2e0c3de39d9d772af98ba7d..9e366b13674538dbf482ffdeee92fc717733ee20 100644
--- a/fs/locks.c
+++ b/fs/locks.c

@@ -1826,6 +1826,11 @@ 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_may_setlease &&
+		    !lease->fl_lmops->lm_may_setlease(lease, fl))
+			goto out;
+

I don't see any locking around this.  What if the condition which
triggers a veto happens after this check, and before the lm_change
below?
Should lm_change implement the veto?  Return -EAGAIN?

The flc_lock is held over this check and any subsequent lease addition.
Is that not sufficient?

quoted

 		/*
 		 * 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 c2ce8ba05d068b451ecf8f513b7e532819a29944..70079beddf61aa32ef01f1114cf0cb3ffaf2131a 100644
--- a/include/linux/filelock.h
+++ b/include/linux/filelock.h

@@ -49,6 +49,20 @@ 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_may_setlease - 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, based on the presence of an existing lease.
+	 *
+	 * Return values:
+	 *   %false: @new and @old conflict
+	 *   %true: No conflict detected
+	 */
+	bool (*lm_may_setlease)(struct file_lease *new, struct file_lease *old);
 };
 
 struct lock_manager {

-- 
2.51.0

-- 
Jeff Layton [off-list ref]