xzmap
str->s_buffer = xzmap(0, p_new_size, PROT_READ | PROT_WRITE,
str->s_buffer = xzmap(0, STDIO_VBUF_SIZE, PROT_READ |
str->s_buffer = xzmap(0, WIDE_VBUF_SIZE, PROT_READ |
extern void *xzmap(void *, size_t, int, int, off_t);