bpf: Support for setting initial receive window

This patch adds suppport for setting the initial advertized window from
within a BPF_SOCK_OPS program. This can be used to support larger
initial cwnd values in environments where it is known to be safe.

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 1 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 47fe0759a877..ef809426b538 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3266,6 +3266,7 @@ static void tcp_connect_init(struct sock *sk)
         const struct dst_entry *dst = __sk_dst_get(sk);
         struct tcp_sock *tp = tcp_sk(sk);
         __u8 rcv_wscale;
+        u32 rcv_wnd;
 
         /* We'll fix this up when we get a response from the other end.
          * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
@@ -3299,13 +3300,17 @@ static void tcp_connect_init(struct sock *sk)
             (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
                 tp->window_clamp = tcp_full_space(sk);
 
+        rcv_wnd = tcp_rwnd_init_bpf(sk);
+        if (rcv_wnd == 0)
+                rcv_wnd = dst_metric(dst, RTAX_INITRWND);
+
         tcp_select_initial_window(tcp_full_space(sk),
                                   tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
                                   &tp->rcv_wnd,
                                   &tp->window_clamp,
                                   sock_net(sk)->ipv4.sysctl_tcp_window_scaling,
                                   &rcv_wscale,
-                                  dst_metric(dst, RTAX_INITRWND));
+                                  rcv_wnd);
 
         tp->rx_opt.rcv_wscale = rcv_wscale;
         tp->rcv_ssthresh = tp->rcv_wnd;