From 6179983ad30c43313e153b35af52bd9ebd7745c3 Mon Sep 17 00:00:00 2001 From: Gerrit Renker Date: Thu, 13 Dec 2007 23:37:55 -0200 Subject: [PATCH] [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 Signed-off-by: Ian McDonald Signed-off-by: Arnaldo Carvalho de Melo Signed-off-by: David S. Miller --- net/dccp/ccid.h | 2 ++ net/dccp/output.c | 30 +++++++++++++++++++++++------- 2 files changed, 25 insertions(+), 7 deletions(-) diff --git a/net/dccp/ccid.h b/net/dccp/ccid.h index e3cdd8afc801..fdeae7b57319 100644 --- a/net/dccp/ccid.h +++ b/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, 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) 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); -- 2.20.1