netdev - Re: [PATCH RFC 02/24] filelock: add a lm_set_conflict lease

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Message-ID: <2a29648675b743befe59fc13c5ed1440d5cbe9ee.camel@kernel.org>
Date: Mon, 18 Mar 2024 07:07:08 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Chuck Lever <chuck.lever@...cle.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner
 <brauner@...nel.org>, Jan Kara <jack@...e.cz>, Alexander Aring
 <alex.aring@...il.com>, Trond Myklebust <trond.myklebust@...merspace.com>, 
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Subject: Re: [PATCH RFC 02/24] filelock: add a lm_set_conflict lease_manager
 callback

On Sun, 2024-03-17 at 10:56 -0400, Chuck Lever 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@...nel.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.
> 
> To make it clear which return value causes add_lease() to abort, I'd
> rather see API contract-style descriptions of the meaning of the
> return values instead of this design note. Something like:
> 
>  * Return values:
>  *   %true: @new and @old conflict
>  *   %false: No conflict detected
> 
> 

Thanks. I added this to the patch in my tree.

> > +	 */
> > +	bool (*lm_set_conflict)(struct file_lease *new, struct file_lease *old);
> >  };
> >  
> >  struct lock_manager {
> > 
> > -- 
> > 2.44.0
> > 
> 

-- 
Jeff Layton <jlayton@...nel.org>