ext2, dax: introduce ext2_dax_aops

In preparation for the dax implementation to start associating dax pages
to inodes via page->mapping, we need to provide a 'struct
address_space_operations' instance for dax. Otherwise, direct-I/O
triggers incorrect page cache assumptions and warnings.

Reviewed-by: Jan Kara <jack@suse.com>
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

fs/ext2/ext2.h

@@ -814,6 +814,7 @@ extern const struct inode_operations ext2_file_inode_operations;
 extern const struct file_operations ext2_file_operations;
 
 /* inode.c */
+extern void ext2_set_file_ops(struct inode *inode);
 extern const struct address_space_operations ext2_aops;
 extern const struct address_space_operations ext2_nobh_aops;
 extern const struct iomap_ops ext2_iomap_ops;