locks: helper functions for delegation breaking

We'll need the same logic for rename and link.

Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -3650,14 +3650,9 @@ int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegate
 	else {
 		error = security_inode_unlink(dir, dentry);
 		if (!error) {
-			error = break_deleg(target, O_WRONLY|O_NONBLOCK);
-			if (error) {
-				if (error == -EWOULDBLOCK && delegated_inode) {
-					*delegated_inode = target;
-					ihold(target);
-				}
+			error = try_break_deleg(target, delegated_inode);
+			if (error)
 				goto out;
-			}
 			error = dir->i_op->unlink(dir, dentry);
 			if (!error)
 				dont_mount(dentry);
@@ -3727,9 +3722,7 @@ static long do_unlinkat(int dfd, const char __user *pathname)
 		iput(inode);	/* truncate the inode here */
 	inode = NULL;
 	if (delegated_inode) {
-		error = break_deleg(delegated_inode, O_WRONLY);
-		iput(delegated_inode);
-		delegated_inode = NULL;
+		error = break_deleg_wait(&delegated_inode);
 		if (!error)
 			goto retry_deleg;
 	}

include/linux/fs.h

@@ -1905,6 +1905,9 @@ extern bool fs_fully_visible(struct file_system_type *);
 
 extern int current_umask(void);
 
+extern void ihold(struct inode * inode);
+extern void iput(struct inode *);
+
 /* /sys/fs */
 extern struct kobject *fs_kobj;
 
@@ -1972,6 +1975,28 @@ static inline int break_deleg(struct inode *inode, unsigned int mode)
 	return 0;
 }
 
+static inline int try_break_deleg(struct inode *inode, struct inode **delegated_inode)
+{
+	int ret;
+
+	ret = break_deleg(inode, O_WRONLY|O_NONBLOCK);
+	if (ret == -EWOULDBLOCK && delegated_inode) {
+		*delegated_inode = inode;
+		ihold(inode);
+	}
+	return ret;
+}
+
+static inline int break_deleg_wait(struct inode **delegated_inode)
+{
+	int ret;
+
+	ret = break_deleg(*delegated_inode, O_WRONLY);
+	iput(*delegated_inode);
+	*delegated_inode = NULL;
+	return ret;
+}
+
 #else /* !CONFIG_FILE_LOCKING */
 static inline int locks_mandatory_locked(struct inode *inode)
 {
@@ -2015,6 +2040,18 @@ static inline int break_deleg(struct inode *inode, unsigned int mode)
 {
 	return 0;
 }
+
+static inline int try_break_deleg(struct inode *inode, struct inode **delegated_inode)
+{
+	return 0;
+}
+
+static inline int break_deleg_wait(struct inode **delegated_inode)
+{
+	BUG();
+	return 0;
+}
+
 #endif /* CONFIG_FILE_LOCKING */
 
 /* fs/open.c */
@@ -2350,8 +2387,6 @@ extern loff_t vfs_llseek(struct file *file, loff_t offset, int whence);
 extern int inode_init_always(struct super_block *, struct inode *);
 extern void inode_init_once(struct inode *);
 extern void address_space_init_once(struct address_space *mapping);
-extern void ihold(struct inode * inode);
-extern void iput(struct inode *);
 extern struct inode * igrab(struct inode *);
 extern ino_t iunique(struct super_block *, ino_t);
 extern int inode_needs_sync(struct inode *inode);