Re: [PATCH RFC 02/24] filelock: add a lm_set_conflict lease_manager callback

[Jeff Layton]

On Wed, 2024-03-20 at 14:13 +0100, Christian Brauner wrote:
> On Fri, Mar 15, 2024 at 12:52:53PM -0400, 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 extra checks when performing a setlease.
> > 
> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > ---
> >  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.
> > +	 */
> > +	bool (*lm_set_conflict)(struct file_lease *new, struct file_lease *old);
> 
> Minor, but it seems a bit misnamed to me. I'd recommend calling this
> lm_may_set_lease() or lm_may_lease().
> 

Yeah, I wasn't thrilled with the name either. Your suggestions sound
reasonable to me. I'll change it to something along those lines.

Thanks,
-- 
Jeff Layton <jlayton@xxxxxxxxxx>