per-superblock default ->d_op

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/dcache.c

@@ -1320,6 +1320,7 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
 		__dget_dlock(parent);
 		dentry->d_parent = parent;
 		dentry->d_sb = parent->d_sb;
+		d_set_d_op(dentry, dentry->d_sb->s_d_op);
 		list_add(&dentry->d_u.d_child, &parent->d_subdirs);
 		spin_unlock(&parent->d_lock);
 	}
@@ -1335,6 +1336,7 @@ struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
 	struct dentry *dentry = d_alloc(NULL, name);
 	if (dentry) {
 		dentry->d_sb = sb;
+		d_set_d_op(dentry, dentry->d_sb->s_d_op);
 		dentry->d_parent = dentry;
 		dentry->d_flags |= DCACHE_DISCONNECTED;
 	}
@@ -1507,6 +1509,7 @@ struct dentry * d_alloc_root(struct inode * root_inode)
 		res = d_alloc(NULL, &name);
 		if (res) {
 			res->d_sb = root_inode->i_sb;
+			d_set_d_op(res, res->d_sb->s_d_op);
 			res->d_parent = res;
 			d_instantiate(res, root_inode);
 		}
@@ -1567,6 +1570,7 @@ struct dentry *d_obtain_alias(struct inode *inode)
 	/* attach a disconnected dentry */
 	spin_lock(&tmp->d_lock);
 	tmp->d_sb = inode->i_sb;
+	d_set_d_op(tmp, tmp->d_sb->s_d_op);
 	tmp->d_inode = inode;
 	tmp->d_flags |= DCACHE_DISCONNECTED;
 	list_add(&tmp->d_alias, &inode->i_dentry);

include/linux/fs.h

@@ -1423,6 +1423,7 @@ struct super_block {
 	 * generic_show_options()
 	 */
 	char __rcu *s_options;
+	const struct dentry_operations *s_d_op; /* default d_op for dentries */
 };
 
 extern struct timespec current_fs_time(struct super_block *sb);