TCP congestion window

Dear all,
First, I apologize you for posing this message although I'm not on the list.

I have some questions. I made the following system call for getting tcp cwnd size of ongoing connection. However, I am always getting the value of "2", which is the initial tcp cwnd size, I think. What I really want to do is to trace tcp cwnd size when I download some big file using "wget"'s http file downloader. For it, I added a new system call shown below and modified the wget source code.

Please cc to me personally in reply. Thanks in advance.

Best Regards,
Yung Yi.

---------------------------------------------------------------------------
asmlinkage int sys_get_winsize(int sockfd)
{
struct socket *sock;
struct sock *sk;
int err;
sock = sockfd_lookup(sockfd, &err);

if (!sock)

       return -1;

sk = sock->sk;
return sk->tp_pinfo.af_tcp.snd_cwnd;
}

Yi,
First of all networking related questions should go to
[email protected]. Now for ur question.
cwnd has got significance in the sending side of a TCP connection. Its the sender that keeps changing the cwnd based on the ACKs recvd. If you are using wget for downloading a file and you are expecting cwnd to change on the wget side, then the answer is that since wget is *only* receiving data, cwnd will not change on wget side. It will change on the other side. If you are checking for cwnd on the other side then please ignore my answer.

Thanx
tomar

Also what you want already exists, so no need to modify the kernel, the TCP_INFO socket option (netinet/tcp.h should have the required definitions in recent glibc)

struct tcp_info info;
int optlen=sizeof(struct tcp_info); if(getsockopt(sk->fd,SOL_TCP,TCP_INFO,(void *)&info,&optlen) < 0)

    return;
  printf("unacked: %d sacked: %d lost: %d retrans: %d fackets: %d\n",
                info.tcpi_unacked,info.tcpi_sacked,info.tcpi_lost,
                info.tcpi_retrans,info.tcpi_fackets);

printf("pmtu: %d rcv_ssthresh: %d rtt: %d rttvar: %d snd_ssthresh:
%d\nsnd_cwnd: %d advmss: %d reordering: %d\n",info.tcpi_pmtu,info.tcpi_rcv_ssthresh,
info.tcpi_rtt,info.tcpi_rttvar,info.tcpi_snd_ssthresh,info.tcpi_snd_cwnd,info.tcpi_advmss,
info.tcpi_reordering)

There's a few more that I don't print there, see the header file.

Pekka Pietikainen

There's also the Web100 patches at http://www.web100.org/
which add full TCP instrumentation, complete with a nice set of GUI diagnostic tools.