On Tue, 2025-10-14 at 16:34 +1100, NeilBrown wrote:
> On Tue, 14 Oct 2025, Jeff Layton wrote:
> > 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?
> > /*
> > * 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 <jlayton@kernel.org>