dccp: Minimise header option overhead in setting the MPS

[mv-sheeva.git] / net / dccp / output.c

diff --git a/net/dccp/output.c b/net/dccp/output.c
index 22a618af48936aa9954978cdf8d94117e02d7bac..27c79bcc6a1ebb97abf091f4d4ea1de4a409362e 100644 (file)
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -161,21 +161,27 @@ 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);
        u32 ccmps = dccp_determine_ccmps(dp);
-       int cur_mps = ccmps ? min(pmtu, ccmps) : pmtu;
+       u32 cur_mps = ccmps ? min(pmtu, ccmps) : pmtu;
 
        /* 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,
-        * TFRC will say it wants TIMESTAMPS, ELAPSED time, etc, for now lets
-        * put a rough estimate for NDP + TIMESTAMP + TIMESTAMP_ECHO + ELAPSED
-        * TIME + TFRC_OPT_LOSS_EVENT_RATE + TFRC_OPT_RECEIVE_RATE + padding to
-        * make it a multiple of 4
+        * Leave enough headroom for common DCCP header options.
+        * This only considers options which may appear on DCCP-Data packets, as
+        * per table 3 in RFC 4340, 5.8. When running out of space for other
+        * options (eg. Ack Vector which can take up to 255 bytes), it is better
+        * to schedule a separate Ack. Thus we leave headroom for the following:
+        *  - 1 byte for Slow Receiver (11.6)
+        *  - 6 bytes for Timestamp (13.1)
+        *  - 10 bytes for Timestamp Echo (13.3)
+        *  - 8 bytes for NDP count (7.7, when activated)
+        *  - 6 bytes for Data Checksum (9.3)
+        *  - %DCCPAV_MIN_OPTLEN bytes for Ack Vector size (11.4, when enabled)
         */
-
-       cur_mps -= roundup(5 + 6 + 10 + 6 + 6 + 6, 4);
+       cur_mps -= roundup(1 + 6 + 10 + dp->dccps_send_ndp_count * 8 + 6 +
+                          (dp->dccps_hc_rx_ackvec ? DCCPAV_MIN_OPTLEN : 0), 4);
 
        /* And store cached results */
        icsk->icsk_pmtu_cookie = pmtu;