fw_cfg_add_file
fw_cfg_add_file("etc/screen-and-debug", &sd, sizeof(sd));
fw_cfg_add_file("bootorder", bootorder, strlen(bootorder) + 1);
fw_cfg_add_file("etc/e820", &e820, e820_len);
void fw_cfg_add_file(const char *, const void *, size_t);