FD_ZERO
#undef FD_ZERO
#define FD_ZERO(maskp)
#define FD_ZERO(p) ((p)->fds_bits[0] = 0)
#define FD_ZERO(p) __builtin_memset((p), 0, sizeof(*(p)))
#define FD_ZERO(p) ((p)->fds_bits[0] = 0)
#define FD_ZERO(x) (*(x) = 0)