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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2007-12-13 20:37:55 -0500
committerDavid S. Miller <davem@davemloft.net>2008-01-28 17:57:59 -0500
commit6179983ad30c43313e153b35af52bd9ebd7745c3 (patch)
tree1b1fcbad582d7aef0505910bdbfecaf833726357 /net/dccp/output.c
parent84a97b0af8c29aa5a47cc5271968a9c6004fb91e (diff)
[DCCP]: Introducing CCMPS
This introduces a CCMPS field for setting a CCID-specific upper bound on the application payload size, as is defined in RFC 4340, section 14. Only the TX CCID is considered in setting this limit, since the RX CCID generates comparatively small (DCCP-Ack) feedback packets. The CCMPS field includes network and transport layer header lengths. The only current CCMPS customer is CCID4 (via RFC 4828). A wrapper is used to allow querying the CCMPS even at times where the CCID modules may not have been fully negotiated yet. In dccp_sync_mss() the variable `mss_now' has been renamed into `cur_mps', to reflect that we are dealing with an MPS, but not an MSS. Since the DCCP code closely follows the TCP code, the identifiers `dccp_sync_mss' and `dccps_mss_cache' have been kept, as they have direct TCP counterparts. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/dccp/output.c')
-rw-r--r--net/dccp/output.c30
1 files changed, 23 insertions, 7 deletions
diff --git a/net/dccp/output.c b/net/dccp/output.c
index 5589a5e581f4..3b763db3d863 100644
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -133,15 +133,31 @@ static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
133 return -ENOBUFS; 133 return -ENOBUFS;
134} 134}
135 135
136/**
137 * dccp_determine_ccmps - Find out about CCID-specfic packet-size limits
138 * We only consider the HC-sender CCID for setting the CCMPS (RFC 4340, 14.),
139 * since the RX CCID is restricted to feedback packets (Acks), which are small
140 * in comparison with the data traffic. A value of 0 means "no current CCMPS".
141 */
142static u32 dccp_determine_ccmps(const struct dccp_sock *dp)
143{
144 const struct ccid *tx_ccid = dp->dccps_hc_tx_ccid;
145
146 if (tx_ccid == NULL || tx_ccid->ccid_ops == NULL)
147 return 0;
148 return tx_ccid->ccid_ops->ccid_ccmps;
149}
150
136unsigned int dccp_sync_mss(struct sock *sk, u32 pmtu) 151unsigned int dccp_sync_mss(struct sock *sk, u32 pmtu)
137{ 152{
138 struct inet_connection_sock *icsk = inet_csk(sk); 153 struct inet_connection_sock *icsk = inet_csk(sk);
139 struct dccp_sock *dp = dccp_sk(sk); 154 struct dccp_sock *dp = dccp_sk(sk);
140 int mss_now = (pmtu - icsk->icsk_af_ops->net_header_len - 155 u32 ccmps = dccp_determine_ccmps(dp);
141 sizeof(struct dccp_hdr) - sizeof(struct dccp_hdr_ext)); 156 int cur_mps = ccmps ? min(pmtu, ccmps) : pmtu;
142 157
143 /* Now subtract optional transport overhead */ 158 /* Account for header lengths and IPv4/v6 option overhead */
144 mss_now -= icsk->icsk_ext_hdr_len; 159 cur_mps -= (icsk->icsk_af_ops->net_header_len + icsk->icsk_ext_hdr_len +
160 sizeof(struct dccp_hdr) + sizeof(struct dccp_hdr_ext));
145 161
146 /* 162 /*
147 * FIXME: this should come from the CCID infrastructure, where, say, 163 * FIXME: this should come from the CCID infrastructure, where, say,
@@ -151,13 +167,13 @@ unsigned int dccp_sync_mss(struct sock *sk, u32 pmtu)
151 * make it a multiple of 4 167 * make it a multiple of 4
152 */ 168 */
153 169
154 mss_now -= ((5 + 6 + 10 + 6 + 6 + 6 + 3) / 4) * 4; 170 cur_mps -= ((5 + 6 + 10 + 6 + 6 + 6 + 3) / 4) * 4;
155 171
156 /* And store cached results */ 172 /* And store cached results */
157 icsk->icsk_pmtu_cookie = pmtu; 173 icsk->icsk_pmtu_cookie = pmtu;
158 dp->dccps_mss_cache = mss_now; 174 dp->dccps_mss_cache = cur_mps;
159 175
160 return mss_now; 176 return cur_mps;
161} 177}
162 178
163EXPORT_SYMBOL_GPL(dccp_sync_mss); 179EXPORT_SYMBOL_GPL(dccp_sync_mss);