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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2010-11-14 17:25:46 +0100
committerGerrit Renker <gerrit@erg.abdn.ac.uk>2010-11-15 07:12:00 +0100
commitd83447f0944e73d690218d79c07762ffa4ceb9e4 (patch)
tree2a9adf943eee50d8c495ac9302692a277d862d92 /net/dccp/output.c
parent18219463c884bfdb7954d298b9edb5194b14d621 (diff)
dccp ccid-2: Schedule Sync as out-of-band mechanism
The problem with Ack Vectors is that i) their length is variable and can in principle grow quite large, ii) it is hard to predict exactly how large they will be. Due to the second point it seems not a good idea to reduce the MPS; in particular when on average there is enough room for the Ack Vector and an increase in length is momentarily due to some burst loss, after which the Ack Vector returns to its normal/average length. The solution taken by this patch is to subtract a minimum-expected Ack Vector length from the MPS, and to defer any larger Ack Vectors onto a separate Sync - but only if indeed there is no space left on the skb. This patch provides the infrastructure to schedule Sync-packets for transporting (urgent) out-of-band data. Its signalling is quicker than scheduling an Ack, since it does not need to wait for new application data. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Diffstat (limited to 'net/dccp/output.c')
-rw-r--r--net/dccp/output.c15
1 files changed, 15 insertions, 0 deletions
diff --git a/net/dccp/output.c b/net/dccp/output.c
index 45b91853f5a..d96dd9d362a 100644
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -283,6 +283,15 @@ static void dccp_xmit_packet(struct sock *sk)
* any local drop will eventually be reported via receiver feedback.
*/
ccid_hc_tx_packet_sent(dp->dccps_hc_tx_ccid, sk, len);
+
+ /*
+ * If the CCID needs to transfer additional header options out-of-band
+ * (e.g. Ack Vectors or feature-negotiation options), it activates this
+ * flag to schedule a Sync. The Sync will automatically incorporate all
+ * currently pending header options, thus clearing the backlog.
+ */
+ if (dp->dccps_sync_scheduled)
+ dccp_send_sync(sk, dp->dccps_gsr, DCCP_PKT_SYNC);
}
/**
@@ -636,6 +645,12 @@ void dccp_send_sync(struct sock *sk, const u64 ackno,
DCCP_SKB_CB(skb)->dccpd_type = pkt_type;
DCCP_SKB_CB(skb)->dccpd_ack_seq = ackno;
+ /*
+ * Clear the flag in case the Sync was scheduled for out-of-band data,
+ * such as carrying a long Ack Vector.
+ */
+ dccp_sk(sk)->dccps_sync_scheduled = 0;
+
dccp_transmit_skb(sk, skb);
}