[PATCH] locks: provide a file lease method enabling cluster-coherent leases

["J. Bruce Fields" <bfields@fieldses.org>]

From: J. Bruce Fields <bfields@fieldses.org>

Currently leases are only kept locally, so there's no way for a distributed
filesystem to enforce them against multiple clients.  We're particularly
interested in the case of nfsd exporting a cluster filesystem, in which
case nfsd needs cluster-coherent leases in order to implement delegations
correctly.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
---
 fs/locks.c         |    5 ++++-
 include/linux/fs.h |    4 ++++
 2 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 3f366e1..40a7f39 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1444,7 +1444,10 @@ int setlease(struct file *filp, long arg, struct file_lock **lease)
 		return error;
 
 	lock_kernel();
-	error = __setlease(filp, arg, lease);
+	if (filp->f_op && filp->f_op->set_lease)
+		error = filp->f_op->set_lease(filp, arg, lease);
+        else
+		error = __setlease(filp, arg, lease);
 	unlock_kernel();
 
 	return error;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7cf0c54..09aefb4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1112,6 +1112,7 @@ struct file_operations {
 	int (*flock) (struct file *, int, struct file_lock *);
 	ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
 	ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
+	int (*set_lease)(struct file *, long, struct file_lock **);
 };
 
 struct inode_operations {
@@ -1137,6 +1138,7 @@ struct inode_operations {
 	ssize_t (*listxattr) (struct dentry *, char *, size_t);
 	int (*removexattr) (struct dentry *, const char *);
 	void (*truncate_range)(struct inode *, loff_t, loff_t);
+	int (*break_lease)(struct inode *, unsigned int);
 };
 
 struct seq_file;
@@ -1463,6 +1465,8 @@ static inline int locks_verify_truncate(struct inode *inode,
 
 static inline int break_lease(struct inode *inode, unsigned int mode)
 {
+	if (inode->i_op && inode->i_op->break_lease)
+		return inode->i_op->break_lease(inode, mode);
 	if (inode->i_flock)
 		return __break_lease(inode, mode);
 	return 0;
-- 
1.5.2.rc3


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