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Date: Thu, 12 Jul 2012 15:29:06 -0700
From: Randy Dunlap <rdunlap@...otime.net>
To: Piotr Sawuk <a9702387@...t.univie.ac.at>
CC: netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: resurrecting tcphealth
On 07/12/2012 01:55 PM, Piotr Sawuk wrote:
> hello! I haven't done any kernel-hacking before, so be patient.
>
> I got as far as to make tcphealth run, but now I need some help:
> how does read-locking work in the tcp_sock struct?
> the original code (for 2.5.1) made a read_lock(&head->lock) with
> struct tcp_ehash_bucket *head = &tcp_ehash[i];
> at the beginning of the for-loop over all sk=head->chain.
> i.e.
> for (i=0; i < tcp_ehash_size; i++) {
> struct tcp_ehash_bucket *head = &tcp_ehash[i];
> struct sock *sk;
> struct tcp_opt *tp;
>
> read_lock(&head->lock);
> for (sk=head->chain; sk; sk=sk->next) {
> if (!TCP_INET_FAMILY(sk->family))
> continue;
>
> and in the new kernel this construction has been replaced by
>
> if (st->state==TCP_SEQ_STATE_ESTABLISHED)
> ...
> static struct tcp_seq_afinfo tcphealth_seq_afinfo
> ...
>
> and the example with proc/net/tcp is seemingly not locking anything. do I
> actually need a read-lock for diagnostic data from tcp_sock? why did the
> original author need to lock the whole chain of tcp_sock?
>
> here's my patch against 3.4.4 so far, any further comments welcome:
Along with what Mr. Hemminger said:
Don't make patches to a stable kernel version. Just make them
to mainline (e.g., 3.5-rc6).
More comments below.
>
> diff -rub linux-3.4.4/include/linux/tcp.h
> linux-3.4.4-heal-lsm/include/linux/tcp.h
> --- linux-3.4.4/include/linux/tcp.h 2012-06-22 20:37:50.000000000 +0200
> +++ linux-3.4.4-heal-lsm/include/linux/tcp.h 2012-07-06 10:23:13.000000000
> +0200
See the 2 lines above. They should be all on one line (the +0200 is
on a separate line). Something along the way split this long line for
you, but this is bad. It corrupts the patch.
> @@ -472,6 +474,15 @@
> * contains related tcp_cookie_transactions fields.
> */
> struct tcp_cookie_values *cookie_values;
> +
> + /*
> + * TCP health monitoring counters.
> + */
> + __u32 dup_acks_sent;
> + __u32 dup_pkts_recv;
> + __u32 acks_sent;
> + __u32 pkts_recv;
> + __u32 last_ack_sent; /* Sequence number of the last ack we sent.
Extra tab before __u32 above.
*/
> };
>
> static inline struct tcp_sock *tcp_sk(const struct sock *sk)
> diff -rub linux-3.4.4/net/ipv4/tcp_input.c
> linux-3.4.4-heal-lsm/net/ipv4/tcp_input.c
> --- linux-3.4.4/net/ipv4/tcp_input.c 2012-06-22 20:37:50.000000000 +0200
> +++ linux-3.4.4-heal-lsm/net/ipv4/tcp_input.c 2012-07-06
> 10:12:12.000000000 +0200
Bad line(s) above.
> @@ -5375,6 +5382,14 @@
>
> tp->rx_opt.saw_tstamp = 0;
>
> + /*
> + * Tcp health monitoring is interested in
> + * total per-connection packet arrivals.
> + * This is in the fast path, but is quick.
> + */
> +
The */
is enough white space; don't add an extra line.
> + tp->pkts_recv++;
> +
> /* pred_flags is 0xS?10 << 16 + snd_wnd
> * if header_prediction is to be made
> * 'S' will always be tp->tcp_header_len >> 2
> diff -rub linux-3.4.4/net/ipv4/tcp_ipv4.c
> linux-3.4.4-heal-lsm/net/ipv4/tcp_ipv4.c
> --- linux-3.4.4/net/ipv4/tcp_ipv4.c 2012-06-22 20:37:50.000000000 +0200
> +++ linux-3.4.4-heal-lsm/net/ipv4/tcp_ipv4.c 2012-07-11 09:34:22.000000000
> +0200
> @@ -2533,6 +2533,82 @@
> return 0;
> }
>
> +
> +/*
> + * Output /proc/net/tcphealth
> + */
> +#define LINESZ 128
> +
> +int tcp_health_seq_show(struct seq_file *seq, void *v)
> +{
> + int len, num;
> + char srcIP[32], destIP[32];
Use tab above for indentation (don't use spaces).
> +
> + unsigned long SmoothedRttEstimate,
> + AcksSent, DupAcksSent, PktsRecv, DupPktsRecv;
> + struct tcp_iter_state *st;
> +
> + if (v == SEQ_START_TOKEN) {
> + seq_printf(seq,
> + "TCP Health Monitoring (established connections only)\n"
> + " -Duplicate ACKs indicate lost or reordered packets on the connection.\n"
> + " -Duplicate Packets Received signal a slow and badly inefficient
> connection.\n"
> + " -RttEst estimates how long future packets will take on a round trip
> over the connection.\n"
> + "id Local Address Remote Address RttEst(ms) AcksSent "
> + "DupAcksSent PktsRecv DupPktsRecv\n");
> + goto out;
> + }
> +
> + /* Loop through established TCP connections */
> + st = seq->private;
> +
> +
> + if (st->state==TCP_SEQ_STATE_ESTABLISHED)
> + {
Kernel style is:
if (st->state == TCP_SEQ_STATE_ESTABLISHED) {
> +/* ; //insert read-lock here */
> + const struct tcp_sock *tp = tcp_sk(v);
> + const struct inet_sock *inet = inet_sk(v);
> + __be32 dest = inet->inet_daddr;
> + __be32 src = inet->inet_rcv_saddr;
> + __u16 destp = ntohs(inet->inet_dport);
> + __u16 srcp = ntohs(inet->inet_sport);
> +
> + num=st->num;
num = st->num;
> + SmoothedRttEstimate = (tp->srtt >> 3);
> + AcksSent = tp->acks_sent;
> + DupAcksSent = tp->dup_acks_sent;
> + PktsRecv = tp->pkts_recv;
> + DupPktsRecv = tp->dup_pkts_recv;
> +
> + sprintf(srcIP, "%lu.%lu.%lu.%lu:%u",
> + ((src >> 24) & 0xFF), ((src >> 16) & 0xFF), ((src >> 8) & 0xFF), (src
> & 0xFF),
> + srcp);
> + sprintf(destIP, "%3d.%3d.%3d.%3d:%u",
> + ((dest >> 24) & 0xFF), ((dest >> 16) & 0xFF), ((dest >> 8) & 0xFF),
> (dest & 0xFF),
> + destp);
> +
> + seq_printf(seq, "%d: %-21s %-21s "
> + "%8lu %8lu %8lu %8lu %8lu%n",
> + num,
> + srcIP,
> + destIP,
> + SmoothedRttEstimate,
> + AcksSent,
> + DupAcksSent,
> + PktsRecv,
> + DupPktsRecv,
> +
> + &len
> + );
> +
> + seq_printf(seq, "%*s\n", LINESZ - 1 - len, "");
> +/* ; //insert read-unlock here */
> + }
> +
> +out:
> + return 0;
> +}
> +
> static const struct file_operations tcp_afinfo_seq_fops = {
> .owner = THIS_MODULE,
> .open = tcp_seq_open,
> @@ -2541,6 +2617,15 @@
> .release = seq_release_net
> };
>
> +static struct tcp_seq_afinfo tcphealth_seq_afinfo = {
> + .name = "tcphealth",
> + .family = AF_INET,
> + .seq_fops = &tcp_afinfo_seq_fops,
> + .seq_ops = {
> + .show = tcp_health_seq_show,
> + },
> +};
> +
> static struct tcp_seq_afinfo tcp4_seq_afinfo = {
> .name = "tcp",
> .family = AF_INET,
> @@ -2552,12 +2637,15 @@
>
> static int __net_init tcp4_proc_init_net(struct net *net)
> {
> - return tcp_proc_register(net, &tcp4_seq_afinfo);
> + int ret=tcp_proc_register(net, &tcp4_seq_afinfo);
int ret = tcp_proc_register(...);
> + if(ret==0) ret=tcp_proc_register(net, &tcphealth_seq_afinfo);
if (ret == 0)
ret = tcp_proc_register(...);
> + return ret;
> }
>
> static void __net_exit tcp4_proc_exit_net(struct net *net)
> {
> tcp_proc_unregister(net, &tcp4_seq_afinfo);
> + tcp_proc_unregister(net, &tcphealth_seq_afinfo);
> }
>
> static struct pernet_operations tcp4_net_ops = {
> diff -rub linux-3.4.4/net/ipv4/tcp_output.c
> linux-3.4.4-heal-lsm/net/ipv4/tcp_output.c
> --- linux-3.4.4/net/ipv4/tcp_output.c 2012-06-22 20:37:50.000000000 +0200
> +++ linux-3.4.4-heal-lsm/net/ipv4/tcp_output.c 2012-07-06
> 17:15:14.000000000 +0200
Bad split lines above.
> @@ -2754,8 +2755,15 @@
> skb_reserve(buff, MAX_TCP_HEADER);
> tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
>
> + /* If the rcv_nxt has not advanced since sending our last ACK, this is
> a duplicate. */
> + if (tcp_sk(sk)->rcv_nxt == tcp_sk(sk)->last_ack_sent)
> + tcp_sk(sk)->dup_acks_sent++;
> + /* Record the total number of acks sent on this connection. */
> + tcp_sk(sk)->acks_sent++;
> +
> /* Send it off, this clears delayed acks for us. */
> TCP_SKB_CB(buff)->when = tcp_time_stamp;
> + tcp_sk(sk)->last_ack_sent = tcp_sk(sk)->rcv_nxt;
Extra tab indentation above.
> tcp_transmit_skb(sk, buff, 0, GFP_ATOMIC);
> }
>
>
> --
--
~Randy
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