code blob

code3.c

struct sock *__inet_lookup_listener(tcp_hashinfo, skb, src_addr, src_port, dst_addr, dst_port)
{
	/*
	 * Use the destination port# to calculate a hash table slot# of the listen socket.
	 * inet_lhashfn() returns a number between 0 and INET_LHTABLE_SIZE-1 (both
	 * inclusive).
	 */
	unsigned int hash = inet_lhashfn(dst_port);

	/* Use this hash slot# to index the global LISTEN hash table */
	struct inet_listen_hashbucket *ilb = tcp_hashinfo->listening_hash[hash];

	/* Keep track of the best matching LISTEN socket thus far, and it’s “score” */
	struct sock *result = NULL, *sk;
	int hi_score = 0;

	for each socket, ‘sk’, in the selected hash bucket, ‘ilb’ {
		/*
		 * Calculate the “score” of this LISTEN socket (sk) against the incoming skb.
		 * Score is computed on some parameters, such as, exact destination port#,
		 * destination IP address closest match (as against matching INADDR_ANY,
		 * for example), with each criteria getting a different weight.
		 */
		score = compute_score(sk, dst_port, dst_addr);
		if (score > hi_score) {
			/* Highest score - best matched socket till now */
			if (sk->sk_reuseport) {
				/*
				 * sk has SO_REUSEPORT feature enabled. Call inet_ehashfn()
				 * with dest_addr, dest_port, src_addr and src_port to compute a
				 * 2nd hash - phash.
				 */
				phash = inet_ehashfn(dst_addr, dst_port, src_addr, src_port);

				/* Select socket from sk’s SO_REUSEPORT group using phash.*/
				result = reuseport_select_sock(sk, phash);
				if (result)
					return result;
			}

			/* Update new best socket and it’s score */
			result = sk;
			hi_score = score;
		}
	}
	return result;
}