dccp ccid-2: Use feature-negotiation to report Ack Ratio changes

This uses the new feature-negotiation framework to signal Ack Ratio changes,
as required by RFC 4341, sec. 6.1.2.

This raises some problems for CCID-2 since it can at the moment not cope
gracefully with Ack Ratio of e.g. 2. A FIXME has thus been added which
reverts to the existing policy of bypassing the Ack Ratio sysctl.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>

2 files changed, 12 insertions, 1 deletions

diff --git a/net/dccp/feat.c b/net/dccp/feat.c
index c847c80d1b97..f94c7c9d1a7f 100644
--- a/net/dccp/feat.c
+++ b/net/dccp/feat.c
@@ -74,6 +74,18 @@ static int dccp_hdlr_seq_win(struct sock *sk, u64 seq_win, bool rx)
 
 static int dccp_hdlr_ack_ratio(struct sock *sk, u64 ratio, bool rx)
 {
+#ifndef __CCID2_COPES_GRACEFULLY_WITH_DYNAMIC_ACK_RATIO_UPDATES__
+        /*
+         * FIXME: This is required until several problems in the CCID-2 code are
+         * resolved. The CCID-2 code currently does not cope well; using dynamic
+         * Ack Ratios greater than 1 caused instabilities. These were manifest
+         * in hangups and long RTO timeouts (1...3 seconds). Until this has been
+         * stabilised, it is safer not to activate dynamic Ack Ratio changes.
+         */
+        dccp_pr_debug("Not changing %s Ack Ratio from 1 to %u\n",
+                      rx ? "RX" : "TX", (u16)ratio);
+        ratio = 1;
+#endif
         if (rx)
                 dccp_sk(sk)->dccps_r_ack_ratio = ratio;
         else
diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 392a5d822b33..11905e0cf8f7 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -189,7 +189,6 @@ int dccp_init_sock(struct sock *sk, const __u8 ctl_sock_initialized)
         dp->dccps_rate_last     = jiffies;
         dp->dccps_role          = DCCP_ROLE_UNDEFINED;
         dp->dccps_service       = DCCP_SERVICE_CODE_IS_ABSENT;
-        dp->dccps_l_ack_ratio   = dp->dccps_r_ack_ratio = 1;
 
         dccp_init_xmit_timers(sk);