rem: tail = (struct userid *) xmalloc (sizeof (struct userid));
add: tail = xmalloc (sizeof (struct userid));
context: getuser (uid_t uid){  register struct userid *tail;  struct passwd *pwent;  for (tail = user_alist; tail; tail = tail->next)    if (tail->id.u == uid)      return tail->name;  pwent = getpwuid (uid);  tail = (struct userid *) xmalloc (sizeof (struct userid));  tail->id.u = uid;  tail->name = pwent ? xstrdup (pwent->pw_name) : NULL;  /* Add to the head of the list, so most recently used is first.  */  tail->next = user_alist;  user_alist = tail;  return tail->name;}