/* get an index key
* - should store the key data in the buffer
- * - should return the amount of amount stored
+ * - should return the amount of data stored
* - not permitted to return an error
* - the netfs data from the cookie being used as the source is
* presented
* @cookie: The cookie representing the cache object
* @mapping: The netfs inode mapping to which the pages will be attached
* @pages: A list of potential netfs pages to be filled
+ * @nr_pages: Number of pages to be read and/or allocated
* @end_io_func: The callback to invoke when and if each page is filled
* @context: An arbitrary piece of data to pass on to end_io_func()
* @gfp: The conditions under which memory allocation should be made