Date: Thu, 22 Jan 2015 15:14:42 -0500
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Jeff Layton <jlayton@primarydata.com>, linux-nfs@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, xfs@oss.sgi.com
Subject: Re: [PATCH 03/20] fs: add FL_LAYOUT lease type
Message-ID: <20150122201442.GJ898@fieldses.org>
References: <1421925006-24231-1-git-send-email-hch@lst.de>
 <1421925006-24231-4-git-send-email-hch@lst.de>
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In-Reply-To: <1421925006-24231-4-git-send-email-hch@lst.de>
Sender: linux-nfs-owner@vger.kernel.org

On Thu, Jan 22, 2015 at 12:09:49PM +0100, Christoph Hellwig wrote:
> This (ab-)uses the file locking code to allow filesystems to recall
> outstanding pNFS layouts on a file.  This new lease type is similar but
> not quite the same as FL_DELEG.  A FL_LAYOUT lease can always be granted,
> an a per-filesystem lock (XFS iolock for the initial implementation)
> ensures not FL_LAYOUT leases granted when we would need to recall them.

So when there's a conflicting operation it's xfs's responsibility to
call break_layout and wait for the recall?

(And what roughly is the set of conflicting operations?)

--b.

> 
> Also included are changes that allow multiple outstanding read
> leases of different types on the same file as long as they have a
> differnt owner.  This wasn't a problem until now as nfsd never set
> FL_LEASE leases, and no one else used FL_DELEG leases, but given that
> nfsd will also issues FL_LAYOUT leases we will have to handle it now.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/locks.c         | 14 ++++++++++----
>  include/linux/fs.h | 16 ++++++++++++++++
>  2 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index 65350a23..6b9772d1 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -137,7 +137,7 @@
>  
>  #define IS_POSIX(fl)	(fl->fl_flags & FL_POSIX)
>  #define IS_FLOCK(fl)	(fl->fl_flags & FL_FLOCK)
> -#define IS_LEASE(fl)	(fl->fl_flags & (FL_LEASE|FL_DELEG))
> +#define IS_LEASE(fl)	(fl->fl_flags & (FL_LEASE|FL_DELEG|FL_LAYOUT))
>  #define IS_OFDLCK(fl)	(fl->fl_flags & FL_OFDLCK)
>  
>  static bool lease_breaking(struct file_lock *fl)
> @@ -1371,6 +1371,8 @@ static void time_out_leases(struct inode *inode, struct list_head *dispose)
>  
>  static bool leases_conflict(struct file_lock *lease, struct file_lock *breaker)
>  {
> +	if ((breaker->fl_flags & FL_LAYOUT) != (lease->fl_flags & FL_LAYOUT))
> +		return false;
>  	if ((breaker->fl_flags & FL_DELEG) && (lease->fl_flags & FL_LEASE))
>  		return false;
>  	return locks_conflict(breaker, lease);
> @@ -1594,11 +1596,14 @@ int fcntl_getlease(struct file *filp)
>   * conflict with the lease we're trying to set.
>   */
>  static int
> -check_conflicting_open(const struct dentry *dentry, const long arg)
> +check_conflicting_open(const struct dentry *dentry, const long arg, int flags)
>  {
>  	int ret = 0;
>  	struct inode *inode = dentry->d_inode;
>  
> +	if (flags & FL_LAYOUT)
> +		return 0;
> +
>  	if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0))
>  		return -EAGAIN;
>  
> @@ -1647,7 +1652,7 @@ generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **pr
>  
>  	spin_lock(&ctx->flc_lock);
>  	time_out_leases(inode, &dispose);
> -	error = check_conflicting_open(dentry, arg);
> +	error = check_conflicting_open(dentry, arg, lease->fl_flags);
>  	if (error)
>  		goto out;
>  
> @@ -1703,7 +1708,7 @@ generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **pr
>  	 * precedes these checks.
>  	 */
>  	smp_mb();
> -	error = check_conflicting_open(dentry, arg);
> +	error = check_conflicting_open(dentry, arg, lease->fl_flags);
>  	if (error) {
>  		locks_unlink_lock_ctx(lease, &ctx->flc_lease_cnt);
>  		goto out;
> @@ -1787,6 +1792,7 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp,
>  			WARN_ON_ONCE(1);
>  			return -ENOLCK;
>  		}
> +
>  		return generic_add_lease(filp, arg, flp, priv);
>  	default:
>  		return -EINVAL;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index f87cb2f..d5658f4 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -875,6 +875,7 @@ static inline struct file *get_file(struct file *f)
>  #define FL_DOWNGRADE_PENDING	256 /* Lease is being downgraded */
>  #define FL_UNLOCK_PENDING	512 /* Lease is being broken */
>  #define FL_OFDLCK	1024	/* lock is "owned" by struct file */
> +#define FL_LAYOUT	2048	/* outstanding pNFS layout */
>  
>  /*
>   * Special return value from posix_lock_file() and vfs_lock_file() for
> @@ -2036,6 +2037,16 @@ static inline int break_deleg_wait(struct inode **delegated_inode)
>  	return ret;
>  }
>  
> +static inline int break_layout(struct inode *inode, bool wait)
> +{
> +	smp_mb();
> +	if (inode->i_flctx && !list_empty_careful(&inode->i_flctx->flc_lease))
> +		return __break_lease(inode,
> +				wait ? O_WRONLY : O_WRONLY | O_NONBLOCK,
> +				FL_LAYOUT);
> +	return 0;
> +}
> +
>  #else /* !CONFIG_FILE_LOCKING */
>  static inline int locks_mandatory_locked(struct file *file)
>  {
> @@ -2091,6 +2102,11 @@ static inline int break_deleg_wait(struct inode **delegated_inode)
>  	return 0;
>  }
>  
> +static inline int break_layout(struct inode *inode, bool wait)
> +{
> +	return 0;
> +}
> +
>  #endif /* CONFIG_FILE_LOCKING */
>  
>  /* fs/open.c */
> -- 
> 1.9.1