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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2009-02-27 22:38:28 +0000
committerDavid S. Miller <davem@davemloft.net>2009-03-02 03:07:23 -0800
commit361a5c1dd0bd7bb2b90e7fe9127b366d3566522e (patch)
tree440150dfa03f976d4ef6d3062744f2185373820d /net/dccp/ackvec.h
parent9ce01461028d595a6f1cd724fbd7a0dd70464fe4 (diff)
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op-kernel-dev-361a5c1dd0bd7bb2b90e7fe9127b366d3566522e.tar.gz
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 <gerrit@erg.abdn.ac.uk> Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/dccp/ackvec.h')
-rw-r--r--net/dccp/ackvec.h3
1 files changed, 3 insertions, 0 deletions
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)
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