mm: export filemap_check_errors() to modules

Can be used by fuse, btrfs and f2fs to replace opencoded variants.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

include/linux/fs.h

@@ -2507,6 +2507,7 @@ extern int __filemap_fdatawrite_range(struct address_space *mapping,
 				loff_t start, loff_t end, int sync_mode);
 extern int filemap_fdatawrite_range(struct address_space *mapping,
 				loff_t start, loff_t end);
+extern int filemap_check_errors(struct address_space *mapping);
 
 extern int vfs_fsync_range(struct file *file, loff_t start, loff_t end,
 			   int datasync);

mm/filemap.c

@@ -254,7 +254,7 @@ void delete_from_page_cache(struct page *page)
 }
 EXPORT_SYMBOL(delete_from_page_cache);
 
-static int filemap_check_errors(struct address_space *mapping)
+int filemap_check_errors(struct address_space *mapping)
 {
 	int ret = 0;
 	/* Check for outstanding write errors */
@@ -266,6 +266,7 @@ static int filemap_check_errors(struct address_space *mapping)
 		ret = -EIO;
 	return ret;
 }
+EXPORT_SYMBOL(filemap_check_errors);
 
 /**
  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range