unpack
size = unpack(fd, zfd, NULL, 0, NULL);
usize = unpack(fd, STDOUT_FILENO,
static off_t unpack(int, int, char *, size_t, off_t *);
smargs = unpack(NULL, hdr.h_to);
const char ** unpack(struct name *, struct name *);
namelist = unpack(hp->h_smopts, to);