nt. server will
accept this connection and increase the sk->sk_ack_backlog -- which is
done in function tcp_check_req().We check wether acceptq is full in
function tcp_v4_syn_recv_sock().

Consider an example:

 After listen(sockfd, 1) system call, sk->sk_max_ack_backlog is set to
1. As we know, sk->sk_ack_backlog is initialized to 0. Assuming accept()
system call is not invoked now.

1. 1st connection comes. invoke sk_acceptq_is_full(). sk-
>sk_ack_backlog=0 sk->sk_max_ack_backlog=1, function return 0 accept
this connection. Increase the sk->sk_ack_backlog
2. 2nd connection comes. invoke sk_acceptq_is_full(). sk-
>sk_ack_backlog=1 sk->sk_max_ack_backlog=1, function return 0 accept
this connection. Increase the sk->sk_ack_backlog
3. 3rd connection comes. invoke sk_acceptq_is_full(). sk-
>sk_ack_backlog=2 sk->sk_max_ack_backlog=1, function return 1. Refuse
this connection.

I think it has bugs. after listen system call. sk->sk_max_ack_backlog=1
but now it can accept 2 connections.

Signed-off-by: Wei Dong <weid@np.css.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Jl?Ž•]x