linux-kernel - Re: [PATCH] allow file system to configure for no leases

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Date:	Tue, 05 Jun 2007 15:33:20 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Peter Staubach <staubach@...hat.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] allow file system to configure for no leases

On Tue, 2007-06-05 at 15:10 -0400, Peter Staubach wrote:
> Hi.
> 
> Attached is a small patch to allow file systems to inform the file
> system independent layers that they don't support file leases.
> 
> The problem is that some file system such as NFSv2 and NFSv3 do
> not have sufficient support to be able to support leases correctly.
> In particular for these two file systems, there is no over the wire
> protocol support.
> 
> Currently, these two file systems fail the fcntl(F_SETLEASE) call
> accidently, due to a reference counting difference.  These file systems
> should fail more consciously, with a proper error to indicate that
> the call is invalid for them.
> 
>     Thanx...
> 
>        ps
> plain text document attachment (devel.tototoday)
> --- linux-2.6.21.i686/fs/nfs/super.c.org
> +++ linux-2.6.21.i686/fs/nfs/super.c
> @@ -522,6 +522,9 @@ static inline void nfs_initialise_sb(str
>  
>  	sb->s_magic = NFS_SUPER_MAGIC;
>  
> +	if (server->nfs_client->cl_nfsversion < 4)
> +		sb->s_flags |= MS_NO_LEASES;
> +

This should be unconditional since we have no support for "lease locks"
under NFSv4 either. The NFSv4 concept of leases and delegations is very
different, since it is really tied to the ability to cache data.

>  	/* We probably want something more informative here */
>  	snprintf(sb->s_id, sizeof(sb->s_id),
>  		 "%x:%x", MAJOR(sb->s_dev), MINOR(sb->s_dev));
> --- linux-2.6.21.i686/fs/locks.c.org
> +++ linux-2.6.21.i686/fs/locks.c
> @@ -1493,6 +1493,8 @@ int fcntl_setlease(unsigned int fd, stru
>  	error = security_file_lock(filp, arg);
>  	if (error)
>  		return error;
> +	if (IS_NO_LEASES(inode))
> +		return -EINVAL;
>  
>  	locks_init_lock(&fl);
>  	error = lease_init(filp, arg, &fl);
> --- linux-2.6.21.i686/include/linux/fs.h.org
> +++ linux-2.6.21.i686/include/linux/fs.h
> @@ -121,6 +121,7 @@ extern int dir_notify_enable;
>  #define MS_SLAVE	(1<<19)	/* change to slave */
>  #define MS_SHARED	(1<<20)	/* change to shared */
>  #define MS_RELATIME	(1<<21)	/* Update atime relative to mtime/ctime. */
> +#define MS_NO_LEASES	(1<<22)	/* fs does not support leases */
>  #define MS_ACTIVE	(1<<30)
>  #define MS_NOUSER	(1<<31)
>  
> @@ -180,6 +181,7 @@ extern int dir_notify_enable;
>  #define IS_NOCMTIME(inode)	((inode)->i_flags & S_NOCMTIME)
>  #define IS_SWAPFILE(inode)	((inode)->i_flags & S_SWAPFILE)
>  #define IS_PRIVATE(inode)	((inode)->i_flags & S_PRIVATE)
> +#define IS_NO_LEASES(inode)	__IS_FLG(inode, MS_NO_LEASES)
>  
>  /* the read-only stuff doesn't really belong here, but any other place is
>     probably as bad and I don't want to create yet another include file. */

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