dccp ccid-3: Remove redundant 'options_received' struct

The `options_received' struct is redundant, since it re-duplicates the existing
`p' and `x_recv' fields. This patch removes the sub-struct and migrates the
format conversion operations (cf. below) to ccid3_hc_tx_parse_options().

                     Why the fields are redundant
                     ----------------------------
The Loss Event Rate p and the Receive Rate x_recv are initially 0 when first 
loading CCID-3, as ccid_new() zeroes out the entire ccid3_hc_tx_sock. 

When Loss Event Rate or Receive Rate options are received, they are stored by
ccid3_hc_tx_parse_options() into the fields `ccid3or_loss_event_rate' and
`ccid3or_receive_rate' of the sub-struct `options_received' in ccid3_hc_tx_sock.

After parsing (considering only the established state - dccp_rcv_established()),
the packet is passed on to ccid_hc_tx_packet_recv(). This calls the CCID-3
specific routine ccid3_hc_tx_packet_recv(), which performs the following copy
operations between fields of ccid3_hc_tx_sock:

 * hctx->options_received.ccid3or_receive_rate is copied into hctx->x_recv,
   after scaling it for fixpoint arithmetic, by 2^64;
 * hctx->options_received.ccid3or_loss_event_rate is copied into hctx->p,
   considering the above special cases; in addition, a value of 0 here needs to
   be mapped into p=0 (when no Loss Event Rate option has been received yet).

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>

net/dccp/ccids/ccid3.c

@@ -370,11 +370,10 @@ static void ccid3_hc_tx_packet_sent(struct sock *sk, int more,
 static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 {
 	struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
-	struct ccid3_options_received *opt_recv = &hctx->options_received;
 	struct tfrc_tx_hist_entry *acked;
 	ktime_t now;
 	unsigned long t_nfb;
-	u32 pinv, r_sample;
+	u32 r_sample;
 
 	/* we are only interested in ACKs */
 	if (!(DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_ACK ||
@@ -404,17 +403,6 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 	r_sample  = dccp_sample_rtt(sk, ktime_us_delta(now, acked->stamp));
 	hctx->rtt = tfrc_ewma(hctx->rtt, r_sample, 9);
 
-	/* Update receive rate in units of 64 * bytes/second */
-	hctx->x_recv = opt_recv->ccid3or_receive_rate;
-	hctx->x_recv <<= 6;
-
-	/* Update loss event rate (which is scaled by 1e6) */
-	pinv = opt_recv->ccid3or_loss_event_rate;
-	if (pinv == 0)
-		hctx->p = 0;
-	else
-		hctx->p = tfrc_invert_loss_event_rate(pinv);
-
 	/*
 	 * Update allowed sending rate X as per draft rfc3448bis-00, 4.2/3
 	 */
@@ -487,7 +475,6 @@ static int ccid3_hc_tx_parse_options(struct sock *sk, u8 packet_type,
 				     u8 option, u8 *optval, u8 optlen)
 {
 	struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
-	struct ccid3_options_received *opt_recv = &hctx->options_received;
 	__be32 opt_val;
 
 	switch (option) {
@@ -504,11 +491,16 @@ static int ccid3_hc_tx_parse_options(struct sock *sk, u8 packet_type,
 		opt_val = ntohl(get_unaligned((__be32 *)optval));
 
 		if (option == TFRC_OPT_RECEIVE_RATE) {
-			opt_recv->ccid3or_receive_rate = opt_val;
+			/* Receive Rate is kept in units of 64 bytes/second */
+			hctx->x_recv = opt_val;
+			hctx->x_recv <<= 6;
+
 			ccid3_pr_debug("%s(%p), RECEIVE_RATE=%u\n",
 				       dccp_role(sk), sk, opt_val);
 		} else {
-			opt_recv->ccid3or_loss_event_rate = opt_val;
+			/* Update the fixpoint Loss Event Rate fraction */
+			hctx->p = tfrc_invert_loss_event_rate(opt_val);
+
 			ccid3_pr_debug("%s(%p), LOSS_EVENT_RATE=%u\n",
 				       dccp_role(sk), sk, opt_val);
 		}

net/dccp/ccids/ccid3.h

@@ -70,11 +70,6 @@ enum ccid3_options {
 	TFRC_OPT_RECEIVE_RATE	 = 194,
 };
 
-struct ccid3_options_received {
-	u32 ccid3or_loss_event_rate;
-	u32 ccid3or_receive_rate;
-};
-
 /* TFRC sender states */
 enum ccid3_hc_tx_states {
 	TFRC_SSTATE_NO_SENT = 1,
@@ -101,7 +96,6 @@ enum ccid3_hc_tx_states {
  * @t_ld - Time last doubled during slow start
  * @t_nom - Nominal send time of next packet
  * @hist - Packet history
- * @options_received - Parsed set of retrieved options
  */
 struct ccid3_hc_tx_sock {
 	u64				x;
@@ -119,7 +113,6 @@ struct ccid3_hc_tx_sock {
 	ktime_t				t_ld;
 	ktime_t				t_nom;
 	struct tfrc_tx_hist_entry	*hist;
-	struct ccid3_options_received	options_received;
 };
 
 static inline struct ccid3_hc_tx_sock *ccid3_hc_tx_sk(const struct sock *sk)