[TCP]: Add tcp_available_congestion_control sysctl.

Create /proc/sys/net/ipv4/tcp_available_congestion_control
that reflects currently available TCP choices.

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

5 files changed, 51 insertions, 0 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index fd3c0c012351..db4280856588 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -351,10 +351,16 @@ tcp_frto - BOOLEAN
         where packet loss is typically due to random radio interference
         rather than intermediate router congestion.
 
+tcp_available_congestion_control - STRING
+        Shows the available congestion control choices that are registered.
+        More congestion control algorithms may be available as modules,
+        but not loaded.
+
 tcp_congestion_control - STRING
         Set the congestion control algorithm to be used for new
         connections. The algorithm "reno" is always available, but
         additional choices may be available based on kernel configuration.
+        Default is set as part of kernel configuration.
 
 somaxconn - INTEGER
         Limit of socket listen() backlog, known in userspace as SOMAXCONN.
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index d98562f1df76..28a48279654d 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -426,6 +426,7 @@ enum
         NET_CIPSOV4_CACHE_BUCKET_SIZE=119,
         NET_CIPSOV4_RBM_OPTFMT=120,
         NET_CIPSOV4_RBM_STRICTVALID=121,
+        NET_TCP_AVAIL_CONG_CONTROL=122,
 };
 
 enum {
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 246916c2321e..6af4baf5b769 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -620,6 +620,9 @@ enum tcp_ca_event {
  * Interface for adding new TCP congestion control handlers
  */
 #define TCP_CA_NAME_MAX 16
+#define TCP_CA_MAX      128
+#define TCP_CA_BUF_MAX  (TCP_CA_NAME_MAX*TCP_CA_MAX)
+
 struct tcp_congestion_ops {
         struct list_head        list;
 
@@ -659,6 +662,7 @@ extern void tcp_init_congestion_control(struct sock *sk);
 extern void tcp_cleanup_congestion_control(struct sock *sk);
 extern int tcp_set_default_congestion_control(const char *name);
 extern void tcp_get_default_congestion_control(char *name);
+extern void tcp_get_available_congestion_control(char *buf, size_t len);
 extern int tcp_set_congestion_control(struct sock *sk, const char *name);
 extern void tcp_slow_start(struct tcp_sock *tp);
 
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 15061b314411..2e770f45d829 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -129,6 +129,23 @@ static int sysctl_tcp_congestion_control(ctl_table *table, int __user *name,
         return ret;
 }
 
+static int proc_tcp_available_congestion_control(ctl_table *ctl,
+                                                 int write, struct file * filp,
+                                                 void __user *buffer, size_t *lenp,
+                                                 loff_t *ppos)
+{
+        ctl_table tbl = { .maxlen = TCP_CA_BUF_MAX, };
+        int ret;
+
+        tbl.data = kmalloc(tbl.maxlen, GFP_USER);
+        if (!tbl.data)
+                return -ENOMEM;
+        tcp_get_available_congestion_control(tbl.data, TCP_CA_BUF_MAX);
+        ret = proc_dostring(&tbl, write, filp, buffer, lenp, ppos);
+        kfree(tbl.data);
+        return ret;
+}
+
 ctl_table ipv4_table[] = {
         {
                 .ctl_name       = NET_IPV4_TCP_TIMESTAMPS,
@@ -731,6 +748,13 @@ ctl_table ipv4_table[] = {
                 .proc_handler   = &proc_dointvec,
         },
 #endif /* CONFIG_NETLABEL */
+        {
+                .ctl_name       = NET_TCP_AVAIL_CONG_CONTROL,
+                .procname       = "tcp_available_congestion_control",
+                .maxlen         = TCP_CA_BUF_MAX,
+                .mode           = 0444,
+                .proc_handler   = &proc_tcp_available_congestion_control,
+        },
         { .ctl_name = 0 }
 };
 
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 1e2982f4acd4..d846d7b95e1f 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -139,6 +139,22 @@ static int __init tcp_congestion_default(void)
 late_initcall(tcp_congestion_default);
 
 
+/* Build string with list of available congestion control values */
+void tcp_get_available_congestion_control(char *buf, size_t maxlen)
+{
+        struct tcp_congestion_ops *ca;
+        size_t offs = 0;
+
+        rcu_read_lock();
+        list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
+                offs += snprintf(buf + offs, maxlen - offs,
+                                 "%s%s",
+                                 offs == 0 ? "" : " ", ca->name);
+
+        }
+        rcu_read_unlock();
+}
+
 /* Get current default congestion control */
 void tcp_get_default_congestion_control(char *name)
 {