@post key and val are the next key/value pair. key is
null-terminated, and val has length len. If the end of the list has
been reached, key and val are NULL, and len is 0. key and val will
not be accessible after rados_omap_get_end() is called on iter, so
if they are needed after that they should be copied.
@param iter iterator to advance
@param key where to store the key of the next omap entry
@param val where to store the value of the next omap entry
@param len where to store the number of bytes in val
@returns 0 on success, negative error code on failure
Get the next omap key/value pair on the object
@pre iter is a valid iterator
@post key and val are the next key/value pair. key is null-terminated, and val has length len. If the end of the list has been reached, key and val are NULL, and len is 0. key and val will not be accessible after rados_omap_get_end() is called on iter, so if they are needed after that they should be copied.
@param iter iterator to advance @param key where to store the key of the next omap entry @param val where to store the value of the next omap entry @param len where to store the number of bytes in val @returns 0 on success, negative error code on failure