dccp ccid-3: remove dead states

This patch is thanks to an investigation by Leandro Sales de Melo and his
colleagues. They worked out two state diagrams which highlight the fact that
the xxx_TERM states in CCID-3/4 are in fact not necessary.

And this can be confirmed by in turn looking at the code: the xxx_TERM states
are only ever set in ccid3_hc_{rx,tx}_exit(): when CCID-3 sets the state
to xxx_TERM, it is at a time where no more processing should be going on,
hence it is not necessary to introduce a dedicated exit state - this is already
implied by unloading the CCID.

Signed-off-by: Gerrit Renker <[e-mail]>

net/dccp/ccids/ccid3.c

···
 	[TFRC_SSTATE_NO_SENT]  = "NO_SENT",
 	[TFRC_SSTATE_NO_FBACK] = "NO_FBACK",
 	[TFRC_SSTATE_FBACK]    = "FBACK",
-	[TFRC_SSTATE_TERM]     = "TERM",
 	};
 
 	return ccid3_state_names[state];
···
 	ccid3_pr_debug("%s(%p, state=%s) - entry\n", dccp_role(sk), sk,
 		       ccid3_tx_state_name(hc->tx_state));
 
+	/* Ignore and do not restart after leaving the established state */
+	if ((1 << sk->sk_state) & ~(DCCPF_OPEN | DCCPF_PARTOPEN))
+		goto out;
+
+	/* Reset feedback state to "no feedback received" */
 	if (hc->tx_state == TFRC_SSTATE_FBACK)
 		ccid3_hc_tx_set_state(sk, TFRC_SSTATE_NO_FBACK);
-	else if (hc->tx_state != TFRC_SSTATE_NO_FBACK)
-		goto out;
 
 	/*
 	 * Determine new allowed sending rate X as per draft rfc3448bis-00, 4.4
···
 	if (unlikely(skb->len == 0))
 		return -EBADMSG;
 
-	switch (hc->tx_state) {
-	case TFRC_SSTATE_NO_SENT:
+	if (hc->tx_state == TFRC_SSTATE_NO_SENT) {
 		sk_reset_timer(sk, &hc->tx_no_feedback_timer, (jiffies +
 			       usecs_to_jiffies(TFRC_INITIAL_TIMEOUT)));
 		hc->tx_last_win_count	= 0;
···
 		ccid3_update_send_interval(hc);
 
 		ccid3_hc_tx_set_state(sk, TFRC_SSTATE_NO_FBACK);
-		break;
-	case TFRC_SSTATE_NO_FBACK:
-	case TFRC_SSTATE_FBACK:
+
+	} else {
 		delay = ktime_us_delta(hc->tx_t_nom, now);
 		ccid3_pr_debug("delay=%ld\n", (long)delay);
 		/*
···
 			return (u32)delay / USEC_PER_MSEC;
 
 		ccid3_hc_tx_update_win_count(hc, now);
-		break;
-	case TFRC_SSTATE_TERM:
-		DCCP_BUG("%s(%p) - Illegal state TERM", dccp_role(sk), sk);
-		return -EINVAL;
 	}
 
 	/* prepare to send now (add options etc.) */
···
 	if (!(DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_ACK ||
 	      DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_DATAACK))
 		return;
-	/* ... and only in the established state */
-	if (hc->tx_state != TFRC_SSTATE_FBACK &&
-	    hc->tx_state != TFRC_SSTATE_NO_FBACK)
-		return;
-
 	/*
 	 * Locate the acknowledged packet in the TX history.
 	 *
···
 {
 	struct ccid3_hc_tx_sock *hc = ccid3_hc_tx_sk(sk);
 
-	ccid3_hc_tx_set_state(sk, TFRC_SSTATE_TERM);
 	sk_stop_timer(sk, &hc->tx_no_feedback_timer);
-
 	tfrc_tx_hist_purge(&hc->tx_hist);
 }
 
···
 	static const char *const ccid3_rx_state_names[] = {
 	[TFRC_RSTATE_NO_DATA] = "NO_DATA",
 	[TFRC_RSTATE_DATA]    = "DATA",
-	[TFRC_RSTATE_TERM]    = "TERM",
 	};
 
 	return ccid3_rx_state_names[state];
···
 {
 	struct ccid3_hc_rx_sock *hc = ccid3_hc_rx_sk(sk);
 	struct dccp_sock *dp = dccp_sk(sk);
-	ktime_t now;
+	ktime_t now = ktime_get_real();
 	s64 delta = 0;
-
-	if (unlikely(hc->rx_state == TFRC_RSTATE_TERM))
-		return;
-
-	now = ktime_get_real();
 
 	switch (fbtype) {
 	case CCID3_FBACK_INITIAL:
···
 static void ccid3_hc_rx_exit(struct sock *sk)
 {
 	struct ccid3_hc_rx_sock *hc = ccid3_hc_rx_sk(sk);
-
-	ccid3_hc_rx_set_state(sk, TFRC_RSTATE_TERM);
 
 	tfrc_rx_hist_purge(&hc->rx_hist);
 	tfrc_lh_cleanup(&hc->rx_li_hist);

net/dccp/ccids/ccid3.h

···
 	TFRC_SSTATE_NO_SENT = 1,
 	TFRC_SSTATE_NO_FBACK,
 	TFRC_SSTATE_FBACK,
-	TFRC_SSTATE_TERM,
 };
 
 /**
···
 enum ccid3_hc_rx_states {
 	TFRC_RSTATE_NO_DATA = 1,
 	TFRC_RSTATE_DATA,
-	TFRC_RSTATE_TERM    = 127,
 };
 
 /**