---

yaml
---
r: 78457
b: refs/heads/master
c: 6179983
h: refs/heads/master
i:
  78455: 58a3b0b
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 84a97b0af8c29aa5a47cc5271968a9c6004fb91e
+refs/heads/master: 6179983ad30c43313e153b35af52bd9ebd7745c3

trunk/net/dccp/ccid.h

@@ -27,6 +27,7 @@ struct tcp_info;
  *  struct ccid_operations  -  Interface to Congestion-Control Infrastructure
  *
  *  @ccid_id: numerical CCID ID (up to %CCID_MAX, cf. table 5 in RFC 4340, 10.)
+ *  @ccid_ccmps: the CCMPS including network/transport headers (0 when disabled)
  *  @ccid_name: alphabetical identifier string for @ccid_id
  *  @ccid_owner: module which implements/owns this CCID
  *  @ccid_hc_{r,t}x_slab: memory pool for the receiver/sender half-connection
@@ -45,6 +46,7 @@ struct tcp_info;
  */
 struct ccid_operations {
 	unsigned char		ccid_id;
+	__u32			ccid_ccmps;
 	const char		*ccid_name;
 	struct module		*ccid_owner;
 	struct kmem_cache	*ccid_hc_rx_slab,

trunk/net/dccp/output.c

@@ -133,15 +133,31 @@ static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
 	return -ENOBUFS;
 }
 
+/**
+ * dccp_determine_ccmps  -  Find out about CCID-specfic packet-size limits
+ * We only consider the HC-sender CCID for setting the CCMPS (RFC 4340, 14.),
+ * since the RX CCID is restricted to feedback packets (Acks), which are small
+ * in comparison with the data traffic. A value of 0 means "no current CCMPS".
+ */
+static u32 dccp_determine_ccmps(const struct dccp_sock *dp)
+{
+	const struct ccid *tx_ccid = dp->dccps_hc_tx_ccid;
+
+	if (tx_ccid == NULL || tx_ccid->ccid_ops == NULL)
+		return 0;
+	return tx_ccid->ccid_ops->ccid_ccmps;
+}
+
 unsigned int dccp_sync_mss(struct sock *sk, u32 pmtu)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct dccp_sock *dp = dccp_sk(sk);
-	int mss_now = (pmtu - icsk->icsk_af_ops->net_header_len -
-		       sizeof(struct dccp_hdr) - sizeof(struct dccp_hdr_ext));
+	u32 ccmps = dccp_determine_ccmps(dp);
+	int cur_mps = ccmps ? min(pmtu, ccmps) : pmtu;
 
-	/* Now subtract optional transport overhead */
-	mss_now -= icsk->icsk_ext_hdr_len;
+	/* Account for header lengths and IPv4/v6 option overhead */
+	cur_mps -= (icsk->icsk_af_ops->net_header_len + icsk->icsk_ext_hdr_len +
+		    sizeof(struct dccp_hdr) + sizeof(struct dccp_hdr_ext));
 
 	/*
 	 * FIXME: this should come from the CCID infrastructure, where, say,
@@ -151,13 +167,13 @@ unsigned int dccp_sync_mss(struct sock *sk, u32 pmtu)
 	 * make it a multiple of 4
 	 */
 
-	mss_now -= ((5 + 6 + 10 + 6 + 6 + 6 + 3) / 4) * 4;
+	cur_mps -= ((5 + 6 + 10 + 6 + 6 + 6 + 3) / 4) * 4;
 
 	/* And store cached results */
 	icsk->icsk_pmtu_cookie = pmtu;
-	dp->dccps_mss_cache = mss_now;
+	dp->dccps_mss_cache = cur_mps;
 
-	return mss_now;
+	return cur_mps;
 }
 
 EXPORT_SYMBOL_GPL(dccp_sync_mss);