0.1. summary When nic supports hardware checksum, tcp only partially calculate the sum and fill the related info into skb three item:
ip_summedcsum_startcsum_offset
when nic driver sends the packet, it will fill these information to hardware’s correspond register.
0.2. call trace 1 2 3 4 5 > tcp_sendmsg
注：__tcp_push_pending_frames和 tcp_push_one最终都调用tcp_write_xmit
0.3. relate source 0.3.1. tcp_prot and tcp_sendmsg 1 2 3 4 2612 struct proto tcp_prot = {... .init = tcp_v4_init_sock,.sendmsg = tcp_sendmsg,
0.3.2. tcp_sendmsg 1 2 3 4 5 6 7 8 9 10 11 12 13 14 916 int tcp_sendmsg (struct kiocb *iocb, struct sock *sk, struct msghdr *msg, 917 size_t size) 987 if (sk->sk_route_caps & NETIF_F_ALL_CSUM)988 skb->ip_summed = CHECKSUM_PARTIAL;989 1096 if (forced_push(tp)) {1097 tcp_mark_push(tp, skb);1098 __tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_PUSH);1099 } else if (skb == tcp_send_head(sk))1100 tcp_push_one(sk, mss_now);
1 2 3 4 5 6 7 8 9 10 11 12 13 1828 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,1829 int nonagle)1830 {1831 1835 if (unlikely(sk->sk_state == TCP_CLOSE))1836 return ;1837 1838 if (tcp_write_xmit(sk, cur_mss, nonagle, 0 , GFP_ATOMIC))1839 tcp_check_probe_timer(sk);1840 }
0.3.3. tcp_push_one 1 2 3 4 5 6 7 8 1845 void tcp_push_one(struct sock *sk, unsigned int mss_now)1846 {1847 struct sk_buff *skb = tcp_send_head(sk);1848 1849 BUG_ON(!skb || skb->len < mss_now);1850 1851 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1 , sk->sk_allocation);1852 }
0.3.4. tcp_write_xmit 1 2 3 4 5 6 1743 static int tcp_write_xmit (struct sock *sk, unsigned int mss_now, int nonagle, 1744 int push_one, gfp_t gfp)1800 if (unlikely(tcp_transmit_skb(sk, skb, 1 , gfp)))1801 break ;
0.3.5. tcp_transmit_skb 1 2 3 4 5 6 7 8 796 static int tcp_transmit_skb (struct sock *sk, struct sk_buff *skb, int clone_it, 797 gfp_t gfp_mask) 799 const struct inet_connection_sock *icsk =892 icsk->icsk_af_ops->send_check(sk, skb);904 err = icsk->icsk_af_ops->queue_xmit(skb, &inet->cork.fl);
0.3.6. tcp_v4_init_sock 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 1875 static int tcp_v4_init_sock (struct sock *sk) 1877 struct inet_connection_sock *icsk =1878 struct tcp_sock *tp =1879 1880 skb_queue_head_init(&tp->out_of_order_queue);1881 tcp_init_xmit_timers(sk);1882 tcp_prequeue_init(tp);1883 1884 icsk->icsk_rto = TCP_TIMEOUT_INIT;1885 tp->mdev = TCP_TIMEOUT_INIT;1886 1887 1892 tp->snd_cwnd = TCP_INIT_CWND;1893 1894 1897 tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;1898 tp->snd_cwnd_clamp = ~0 ;1899 tp->mss_cache = TCP_MSS_DEFAULT;1900 1901 tp->reordering = sysctl_tcp_reordering;1902 icsk->icsk_ca_ops = &tcp_init_congestion_ops;1903 1904 sk->sk_state = TCP_CLOSE;1905 1906 sk->sk_write_space = sk_stream_write_space;1907 sock_set_flag(sk, SOCK_USE_WRITE_QUEUE);1908 1909 icsk->icsk_af_ops = &ipv4_specific;1910 icsk->icsk_sync_mss = tcp_sync_mss;
0.3.7. inet_connection_sock_af_ops 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1844 const struct inet_connection_sock_af_ops ipv4_specific =1845 .queue_xmit = ip_queue_xmit,1846 .send_check = tcp_v4_send_check,1847 .rebuild_header = inet_sk_rebuild_header,1848 .conn_request = tcp_v4_conn_request,1849 .syn_recv_sock = tcp_v4_syn_recv_sock,1850 .get_peer = tcp_v4_get_peer,1851 .net_header_len = sizeof (struct iphdr),1852 .setsockopt = ip_setsockopt,1853 .getsockopt = ip_getsockopt,1854 .addr2sockaddr = inet_csk_addr2sockaddr,1855 .sockaddr_len = sizeof (struct sockaddr_in),1856 .bind_conflict = inet_csk_bind_conflict,1857 #ifdef CONFIG_COMPAT 1858 .compat_setsockopt = compat_ip_setsockopt,1859 .compat_getsockopt = compat_ip_getsockopt,1860 #endif 1861 };
0.3.8. tcp_v4_send_check 1 2 3 4 5 6 7 546 547 void tcp_v4_send_check (struct sock *sk, struct sk_buff *skb) 549 const struct inet_sock *inet =550 551 __tcp_v4_send_check(skb, inet->inet_saddr, inet->inet_daddr);552 }
0.3.9. __tcp_v4_send_check 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 529 static void __tcp_v4_send_check(struct sk_buff *skb,530 __be32 saddr, __be32 daddr)531 {532 struct tcphdr *th =533 534 if (skb->ip_summed == CHECKSUM_PARTIAL) {535 th->check = ~tcp_v4_check(skb->len, saddr, daddr, 0 );536 skb->csum_start = skb_transport_header(skb) - skb->head;537 skb->csum_offset = offsetof(struct tcphdr, check);538 } else {539 th->check = tcp_v4_check(skb->len, saddr, daddr,540 csum_partial(th,541 th->doff << 2 ,542 skb->csum));543 }544 }
neigh operations
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 129 static const struct neigh_ops arp_generic_ops =130 .family = AF_INET,131 .solicit = arp_solicit,132 .error_report = arp_error_report,133 .output = neigh_resolve_output,134 .connected_output = neigh_connected_output,135 };136 137 static const struct neigh_ops arp_hh_ops =138 .family = AF_INET,139 .solicit = arp_solicit,140 .error_report = arp_error_report,141 .output = neigh_resolve_output,142 .connected_output = neigh_resolve_output,143 };144 145 static const struct neigh_ops arp_direct_ops =146 .family = AF_INET,147 .output = neigh_direct_output,148 .connected_output = neigh_direct_output,149 };150 151 static const struct neigh_ops arp_broken_ops =152 .family = AF_INET,153 .solicit = arp_solicit,154 .error_report = arp_error_report,155 .output = neigh_compat_output,156 .connected_output = neigh_compat_output,157 };
1 2 3 4 5 1280 int neigh_resolve_output (struct neighbour *neigh, struct sk_buff *skb) 1304 if (err >= 0 )1305 rc = dev_queue_xmit(skb);
1 2 3 4 2511 int dev_queue_xmit (struct sk_buff *skb) 2561 rc = dev_hard_start_xmit(skb, dev, txq);
0.3.10. dev_hard_start_xmit 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 2184 int dev_hard_start_xmit (struct sk_buff *skb, struct net_device *dev, 2185 struct netdev_queue *txq)2204 features = netif_skb_features(skb);2215 if (netif_needs_gso(skb, features)) {2216 if (unlikely(dev_gso_segment(skb, features)))2217 goto out_kfree_skb;2218 if (skb->next)2219 goto gso;2220 } else {2221 if (skb_needs_linearize(skb, features) &&2222 __skb_linearize(skb))2223 goto out_kfree_skb;2224 2225 2229 if (skb->ip_summed == CHECKSUM_PARTIAL) {2230 skb_set_transport_header(skb,2231 skb_checksum_start_offset(skb));2232 if (!(features & NETIF_F_ALL_CSUM) &&2233 skb_checksum_help(skb))2234 goto out_kfree_skb;2235 }2236 }2239 rc = ops->ndo_start_xmit(skb, dev);
0.3.11. nic dirver e1000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 847 static const struct net_device_ops e1000_netdev_ops =848 .ndo_open = e1000_open,849 .ndo_stop = e1000_close,850 .ndo_start_xmit = e1000_xmit_frame,851 .ndo_get_stats = e1000_get_stats,852 .ndo_set_rx_mode = e1000_set_rx_mode,853 .ndo_set_mac_address = e1000_set_mac,854 .ndo_tx_timeout = e1000_tx_timeout,855 .ndo_change_mtu = e1000_change_mtu,856 .ndo_do_ioctl = e1000_ioctl,857 .ndo_validate_addr = eth_validate_addr,858 .ndo_vlan_rx_add_vid = e1000_vlan_rx_add_vid,859 .ndo_vlan_rx_kill_vid = e1000_vlan_rx_kill_vid,860 #ifdef CONFIG_NET_POLL_CONTROLLER 861 .ndo_poll_controller = e1000_netpoll,862 #endif 863 .ndo_fix_features = e1000_fix_features,864 .ndo_set_features = e1000_set_features,865 };
1 2 3 4 5 6 5013 static netdev_tx_t e1000_xmit_frame (struct sk_buff *skb, 5014 struct net_device *netdev)5113 else if (e1000_tx_csum(tx_ring, skb))5114 tx_flags |= E1000_TX_FLAGS_CSUM;
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 2781 static bool e1000_tx_csum (struct e1000_adapter *adapter, 2782 struct e1000_tx_ring *tx_ring, struct sk_buff *skb)2784 struct e1000_context_desc *context_desc ;2785 struct e1000_buffer *buffer_info ;2786 unsigned int i;2787 u8 css;2788 u32 cmd_len = E1000_TXD_CMD_DEXT;2789 2790 if (skb->ip_summed != CHECKSUM_PARTIAL)2791 return false ;2792 2793 switch (skb->protocol) {2794 case cpu_to_be16 (ETH_P_IP) :if (ip_hdr(skb)->protocol == IPPROTO_TCP) 2797 break ;2798 case cpu_to_be16 (ETH_P_IPV6) :if (ipv6_hdr(skb)->nexthdr == IPPROTO_TCP) 2802 break ;2803 default :2804 if (unlikely(net_ratelimit()))2805 e_warn(drv, "checksum_partial proto=%x!\n" ,2806 skb->protocol);2807 break ;2808 }2809 2810 css = skb_checksum_start_offset(skb);2811 2812 i = tx_ring->next_to_use;2813 buffer_info = &tx_ring->buffer_info[i];2814 context_desc = E1000_CONTEXT_DESC(*tx_ring, i);2815 2816 context_desc->lower_setup.ip_config = 0 ;2817 context_desc->upper_setup.tcp_fields.tucss = css;2818 context_desc->upper_setup.tcp_fields.tucso =2819 css + skb->csum_offset;2820 context_desc->upper_setup.tcp_fields.tucse = 0 ;2821 context_desc->tcp_seg_setup.data = 0 ;2822 context_desc->cmd_and_length = cpu_to_le32(cmd_len);2823 2824 buffer_info->time_stamp = jiffies;2825 buffer_info->next_to_watch = i;2826 2827 if (unlikely(++i == tx_ring->count)) i = 0 ;
1 2 3 4 5 6 7 8 9 10 11 12 13 201 static struct pci_driver e1000_driver =202 .name = e1000_driver_name,203 .id_table = e1000_pci_tbl,204 .probe = e1000_probe,205 .remove = __devexit_p(e1000_remove),206 #ifdef CONFIG_PM 207 208 .suspend = e1000_suspend,209 .resume = e1000_resume,210 #endif 211 .shutdown = e1000_shutdown,212 .err_handler = &e1000_err_handler213 };
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 942 static int __devinit e1000_probe (struct pci_dev *pdev, 943 const struct pci_device_id *ent) 945 struct net_device *netdev ;946 struct e1000_adapter *adapter ;1065 if (hw->mac_type >= e1000_82543) {1066 netdev->hw_features = NETIF_F_SG |1067 NETIF_F_HW_CSUM |1068 NETIF_F_HW_VLAN_RX;1069 netdev->features = NETIF_F_HW_VLAN_TX |1070 NETIF_F_HW_VLAN_FILTER;1071 }1072 1073 if ((hw->mac_type >= e1000_82544) &&1074 (hw->mac_type != e1000_82547))1075 netdev->hw_features |= NETIF_F_TSO;1076 1077 netdev->priv_flags |= IFF_SUPP_NOFCS;1078 1079 netdev->features |= netdev->hw_features;1080 netdev->hw_features |= NETIF_F_RXCSUM;1081 netdev->hw_features |= NETIF_F_RXFCS;