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

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Date: Sun, 17 Mar 2024 10:56:37 -0400
From: Chuck Lever <chuck.lever@...cle.com>
To: Jeff Layton <jlayton@...nel.org>
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>,
        Anna Schumaker <anna@...nel.org>, Steve French <sfrench@...ba.org>,
        Paulo Alcantara <pc@...guebit.com>,
        Ronnie Sahlberg <ronniesahlberg@...il.com>,
        Shyam Prasad N <sprasad@...rosoft.com>, Tom Talpey <tom@...pey.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        David Howells <dhowells@...hat.com>, Tyler Hicks <code@...icks.com>,
        Neil Brown <neilb@...e.de>, Olga Kornievskaia <kolga@...app.com>,
        Dai Ngo <Dai.Ngo@...cle.com>, Miklos Szeredi <miklos@...redi.hu>,
        Amir Goldstein <amir73il@...il.com>,
        Namjae Jeon <linkinjeon@...nel.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
        netfs@...ts.linux.dev, ecryptfs@...r.kernel.org,
        linux-unionfs@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH RFC 02/24] filelock: add a lm_set_conflict lease_manager
 callback

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


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

-- 
Chuck Lever