From 361a5c1dd0bd7bb2b90e7fe9127b366d3566522e Mon Sep 17 00:00:00 2001 From: Gerrit Renker Date: Fri, 27 Feb 2009 22:38:28 +0000 Subject: dccp: Minimise header option overhead in setting the MPS This patch resolves a long-standing FIXME to dynamically update the Maximum Packet Size depending on actual options usage. It uses the flags set by the feature-negotiation infrastructure to compute the required header option size. Most options are fixed-size, a notable exception are Ack Vectors (required currently only by CCID-2). These can have any length between 3 and 1020 bytes. As a result of testing, 16 bytes (2 bytes for type/length plus 14 Ack Vector cells) have been found to be sufficient for loss-free situations. There are currently no CCID-specific header options which may appear on data packets, thus it is not necessary to define a corresponding CCID field as suggested in the old comment. Further changes: ---------------- Adjusted the type of 'cur_mps' to match the unsigned return type of the function. Signed-off-by: Gerrit Renker Acked-by: Ian McDonald Signed-off-by: David S. Miller --- net/dccp/ackvec.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'net/dccp/ackvec.h') diff --git a/net/dccp/ackvec.h b/net/dccp/ackvec.h index 45f95e5..7ea557b 100644 --- a/net/dccp/ackvec.h +++ b/net/dccp/ackvec.h @@ -20,6 +20,9 @@ /* We can spread an ack vector across multiple options */ #define DCCP_MAX_ACKVEC_LEN (DCCP_SINGLE_OPT_MAXLEN * 2) +/* Estimated minimum average Ack Vector length - used for updating MPS */ +#define DCCPAV_MIN_OPTLEN 16 + #define DCCP_ACKVEC_STATE_RECEIVED 0 #define DCCP_ACKVEC_STATE_ECN_MARKED (1 << 6) #define DCCP_ACKVEC_STATE_NOT_RECEIVED (3 << 6) -- cgit v1.1