[NETROM]: Implement G8PZT Circuit reset for NET/ROM

NET/ROM is lacking a connection reset like TCP's RST flag which at times
may result in a connecting having to slowly timing out instead of just being
reset.  An earlier attempt to reset the connection by sending a
NR_CONNACK | NR_CHOKE_FLAG transport was inacceptable as it did result in
crashes of BPQ systems.  An alternative approach of introducing a new
transport type 7 (NR_RESET) has be implemented several years ago in
Paula Jayne Dowie G8PZT's Xrouter.

Implement NR_RESET for Linux's NET/ROM but like any messing with the state
engine consider this experimental for now and thus control it by a sysctl
(net.netrom.reset) which for the time being defaults to off.

Signed-off-by: Ralf Baechle DL5RB <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 10 deletions

diff --git a/net/netrom/af_netrom.c b/net/netrom/af_netrom.c
index 02b1ab52dbbf..8c3d3a78481e 100644
--- a/net/netrom/af_netrom.c
+++ b/net/netrom/af_netrom.c
@@ -56,6 +56,7 @@ int sysctl_netrom_transport_requested_window_size = NR_DEFAULT_WINDOW;
 int sysctl_netrom_transport_no_activity_timeout   = NR_DEFAULT_IDLE;
 int sysctl_netrom_routing_control                 = NR_DEFAULT_ROUTING;
 int sysctl_netrom_link_fails_count                = NR_DEFAULT_FAILS;
+int sysctl_netrom_reset_circuit                   = NR_DEFAULT_RESET;
 
 static unsigned short circuit = 0x101;
 
@@ -908,17 +909,17 @@ int nr_rx_frame(struct sk_buff *skb, struct net_device *dev)
         if (frametype != NR_CONNREQ) {
                 /*
                  * Here it would be nice to be able to send a reset but
-                 * NET/ROM doesn't have one. The following hack would
-                 * have been a way to extend the protocol but apparently
-                 * it kills BPQ boxes... :-(
+                 * NET/ROM doesn't have one.  We've tried to extend the protocol
+                 * by sending NR_CONNACK | NR_CHOKE_FLAGS replies but that
+                 * apparently kills BPQ boxes... :-(
+                 * So now we try to follow the established behaviour of
+                 * G8PZT's Xrouter which is sending packets with command type 7
+                 * as an extension of the protocol.
                  */
-#if 0
-                /*
-                 * Never reply to a CONNACK/CHOKE.
-                 */
-                if (frametype != NR_CONNACK || flags != NR_CHOKE_FLAG)
-                        nr_transmit_refusal(skb, 1);
-#endif
+                if (sysctl_netrom_reset_circuit &&
+                    (frametype != NR_RESET || flags != 0))
+                        nr_transmit_reset(skb, 1);
+
                 return 0;
         }