netfs_advance_write
size_t netfs_advance_write(struct netfs_io_request *wreq,
part = netfs_advance_write(creq, cache, fpos + cache->submit_off,
part = netfs_advance_write(wreq, stream, fpos + stream->submit_off,
part = netfs_advance_write(wreq, stream, fpos + stream->submit_off,