sctp: Implement quick failover draft from tsvwg

I've seen several attempts recently made to do quick failover of sctp transports
by reducing various retransmit timers and counters.  While its possible to
implement a faster failover on multihomed sctp associations, its not
particularly robust, in that it can lead to unneeded retransmits, as well as
false connection failures due to intermittent latency on a network.

Instead, lets implement the new ietf quick failover draft found here:
http://tools.ietf.org/html/draft-nishida-tsvwg-sctp-failover-05

This will let the sctp stack identify transports that have had a small number of
errors, and avoid using them quickly until their reliability can be
re-established.  I've tested this out on two virt guests connected via multiple
isolated virt networks and believe its in compliance with the above draft and
works well.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Vlad Yasevich <vyasevich@gmail.com>
CC: Sridhar Samudrala <sri@us.ibm.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: linux-sctp@vger.kernel.org
CC: joe@perches.com
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 0 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 5f3ef7f7fcec..406a5226220d 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1440,6 +1440,20 @@ path_max_retrans - INTEGER
 
         Default: 5
 
+pf_retrans - INTEGER
+        The number of retransmissions that will be attempted on a given path
+        before traffic is redirected to an alternate transport (should one
+        exist).  Note this is distinct from path_max_retrans, as a path that
+        passes the pf_retrans threshold can still be used.  Its only
+        deprioritized when a transmission path is selected by the stack.  This
+        setting is primarily used to enable fast failover mechanisms without
+        having to reduce path_max_retrans to a very low value.  See:
+        http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
+        for details.  Note also that a value of pf_retrans > path_max_retrans
+        disables this feature
+
+        Default: 0
+
 rto_initial - INTEGER
         The initial round trip timeout value in milliseconds that will be used
         in calculating round trip times.  This is the initial time interval