fs: export empty_aops

With the ->sync_page() hook gone, we have a few users that
add their own static address_space_operations without any
functions defined.

fs/inode.c already has an empty_aops that it uses for init
purposes. Lets export that and use it in the places where
an otherwise empty aops was defined.
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

fs/inode.c

@@ -124,6 +124,14 @@ __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_wb_list_lock);
  */
 static DECLARE_RWSEM(iprune_sem);
 
+/*
+ * Empty aops. Can be used for the cases where the user does not
+ * define any of the address_space operations.
+ */
+const struct address_space_operations empty_aops = {
+};
+EXPORT_SYMBOL(empty_aops);
+
 /*
  * Statistics gathering..
  */
@@ -176,7 +184,6 @@ int proc_nr_inodes(ctl_table *table, int write,
  */
 int inode_init_always(struct super_block *sb, struct inode *inode)
 {
-	static const struct address_space_operations empty_aops;
 	static const struct inode_operations empty_iops;
 	static const struct file_operations empty_fops;
 	struct address_space *const mapping = &inode->i_data;

fs/nilfs2/page.c

@@ -495,8 +495,6 @@ unsigned nilfs_page_count_clean_buffers(struct page *page,
 void nilfs_mapping_init(struct address_space *mapping,
 			struct backing_dev_info *bdi)
 {
-	static const struct address_space_operations empty_aops;
-
 	mapping->host = NULL;
 	mapping->flags = 0;
 	mapping_set_gfp_mask(mapping, GFP_NOFS);

fs/ubifs/xattr.c

@@ -56,6 +56,7 @@
  */
 
 #include "ubifs.h"
+#include <linux/fs.h>
 #include <linux/slab.h>
 #include <linux/xattr.h>
 #include <linux/posix_acl_xattr.h>
@@ -80,7 +81,6 @@ enum {
 };
 
 static const struct inode_operations none_inode_operations;
-static const struct address_space_operations none_address_operations;
 static const struct file_operations none_file_operations;
 
 /**
@@ -130,7 +130,7 @@ static int create_xattr(struct ubifs_info *c, struct inode *host,
 	}
 
 	/* Re-define all operations to be "nothing" */
-	inode->i_mapping->a_ops = &none_address_operations;
+	inode->i_mapping->a_ops = &empty_aops;
 	inode->i_op = &none_inode_operations;
 	inode->i_fop = &none_file_operations;
 

include/linux/fs.h

@@ -613,6 +613,8 @@ struct address_space_operations {
 	int (*error_remove_page)(struct address_space *, struct page *);
 };
 
+extern const struct address_space_operations empty_aops;
+
 /*
  * pagecache_write_begin/pagecache_write_end must be used by general code
  * to write into the pagecache.