[TCP]: Allow choosing TCP congestion control via sockopt.

Allow using setsockopt to set TCP congestion control to use on a per
socket basis.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 44 insertions, 2 deletions

diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 665394a63ae4..4970d10a7785 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -21,7 +21,7 @@ static struct tcp_congestion_ops *tcp_ca_find(const char *name)
 {
         struct tcp_congestion_ops *e;
 
-        list_for_each_entry(e, &tcp_cong_list, list) {
+        list_for_each_entry_rcu(e, &tcp_cong_list, list) {
                 if (strcmp(e->name, name) == 0)
                         return e;
         }
@@ -77,6 +77,9 @@ void tcp_init_congestion_control(struct tcp_sock *tp)
 {
         struct tcp_congestion_ops *ca;
 
+        if (tp->ca_ops != &tcp_init_congestion_ops)
+                return;
+
         rcu_read_lock();
         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
                 if (try_module_get(ca->owner)) {
@@ -139,6 +142,34 @@ void tcp_get_default_congestion_control(char *name)
         rcu_read_unlock();
 }
 
+/* Change congestion control for socket */
+int tcp_set_congestion_control(struct tcp_sock *tp, const char *name)
+{
+        struct tcp_congestion_ops *ca;
+        int err = 0;
+
+        rcu_read_lock();
+        ca = tcp_ca_find(name);
+        if (ca == tp->ca_ops)
+                goto out;
+
+        if (!ca)
+                err = -ENOENT;
+
+        else if (!try_module_get(ca->owner))
+                err = -EBUSY;
+
+        else {
+                tcp_cleanup_congestion_control(tp);
+                tp->ca_ops = ca;
+                if (tp->ca_ops->init)
+                        tp->ca_ops->init(tp);
+        }
+ out:
+        rcu_read_unlock();
+        return err;
+}
+
 /*
  * TCP Reno congestion control
  * This is special case used for fallback as well.
@@ -192,4 +223,15 @@ struct tcp_congestion_ops tcp_reno = {
         .min_cwnd       = tcp_reno_min_cwnd,
 };
 
-EXPORT_SYMBOL_GPL(tcp_reno);
+/* Initial congestion control used (until SYN)
+ * really reno under another name so we can tell difference
+ * during tcp_set_default_congestion_control
+ */
+struct tcp_congestion_ops tcp_init_congestion_ops  = {
+        .name           = "",
+        .owner          = THIS_MODULE,
+        .ssthresh       = tcp_reno_ssthresh,
+        .cong_avoid     = tcp_reno_cong_avoid,
+        .min_cwnd       = tcp_reno_min_cwnd,
+};
+EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);