Quagga bgp_accept code

Question

我正在努力理解下面（下面的代码）在做什么，并且正在努力理解sockunions的概念。有人能帮我吗？这与线程和线程文件描述符有什么关系？

提前感谢您的帮助，并愿意接受您可以推荐的任何资源！

Sarah

---

static int
bgp_accept (struct thread *thread)
{
int bgp_sock;
int accept_sock;
union sockunion su;
struct bgp_listener *listener = THREAD_ARG(thread);
struct peer *peer;
struct peer *peer1;
char buf[SU_ADDRSTRLEN];
/* Register accept thread. */
accept_sock = THREAD_FD (thread);
    if (accept_sock < 0)
    {
    zlog_err ("accept_sock is nevative value %d", accept_sock);
    return -1;
    }
listener->thread = thread_add_read (master, bgp_accept, listener, accept_sock);
/* Accept client connection. */
bgp_sock = sockunion_accept (accept_sock, &su);
    if (bgp_sock < 0)
    {
...