Linux Wireless架構總結

1.  無線網絡驅動(ath9k_htc)

     ath9k_htc是一個基於USB接口的SoftMAC無線網絡適配器。爲了其驅動能正常工作，首先必須調用usb_register來註冊驅動定義的usb_driver，以藉助USB Core的力量來處理與USB協議相關的事件。其代碼如下：

static struct usb_driver ath9k_hif_usb_driver = {
    .name = KBUILD_MODNAME,
    .probe = ath9k_hif_usb_probe,
    .disconnect = ath9k_hif_usb_disconnect,
#ifdef CONFIG_PM
    .suspend = ath9k_hif_usb_suspend,
    .resume = ath9k_hif_usb_resume,
    .reset_resume = ath9k_hif_usb_resume,
#endif
    .id_table = ath9k_hif_usb_ids,
    .soft_unbind = 1,
};

2. 關鍵數據結構

1) struct ieee80211_hw: 它包含802.11 PHY的配置和硬件信息。

2.1 各層間關鍵數據接口

3. USB無線適配器枚舉過程 

     當此基於USB接口的無線網絡適配器被枚舉時，ath9k_hif_usb_probe將被調用。其調用流程如下圖所示：

3.1 struct ieee80211_ops 實例 ath9k_htc_ops(驅動實現)

       ath9k_htc_ops: mac80211通過這些回調函數回調driver的處理函數。ath9k_htc爲了接受mac80211的管理，它必須首先向mac80211註冊，以申明自己的存在，從而可以接受mac80211的調用。

struct ieee80211_ops ath9k_htc_ops = {
    .tx                 = ath9k_htc_tx,  // 發送mac80211要求發送的幀
    .start              = ath9k_htc_start, // 第一個被attach到此硬件的net_device被enable之前被調用,之後，可以接收幀數據
    .stop               = ath9k_htc_stop,  // 最後一個被attach到此硬件的net_device被disable之後被調用,之後，不可以接收幀數據
    .add_interface      = ath9k_htc_add_interface, // 當一個被attach到此硬件的net_device被enable時被調用
    .remove_interface   = ath9k_htc_remove_interface, // 通知driver一個接口將要going down
    .config             = ath9k_htc_config,           // mac802.11調用它修改硬件配置
    .configure_filter   = ath9k_htc_configure_filter, // 配置設備的接收過濾器
    .sta_add            = ath9k_htc_sta_add,
    .sta_remove         = ath9k_htc_sta_remove,
    .conf_tx            = ath9k_htc_conf_tx,
    .bss_info_changed   = ath9k_htc_bss_info_changed,
    .set_key            = ath9k_htc_set_key,
    .get_tsf            = ath9k_htc_get_tsf,
    .set_tsf            = ath9k_htc_set_tsf,
    .reset_tsf          = ath9k_htc_reset_tsf,
    .ampdu_action       = ath9k_htc_ampdu_action,
    .sw_scan_start      = ath9k_htc_sw_scan_start,
    .sw_scan_complete   = ath9k_htc_sw_scan_complete,
    .set_rts_threshold  = ath9k_htc_set_rts_threshold,
    .rfkill_poll        = ath9k_htc_rfkill_poll_state,
    .set_coverage_class = ath9k_htc_set_coverage_class,
    .set_bitrate_mask   = ath9k_htc_set_bitrate_mask,
};

3.2 struct cfg80211_ops 實例 mac80211_config_ops(mac80211實現)  

   cfg80211_ops定義了無線配置的操作，在它的增加虛擬接口(ieee80211_add_iface)中，它將創建並註冊net_device。在mac80211中，其定義如下所示：

struct cfg80211_ops mac80211_config_ops = {
    .add_virtual_intf = ieee80211_add_iface, //使用給定的名字創建一個"虛擬接口",在wiphy的命名空間中創建net_device並返回
    .del_virtual_intf = ieee80211_del_iface, //刪除由ifindex指定的"虛擬接口"
    .change_virtual_intf = ieee80211_change_iface,
    .add_key = ieee80211_add_key,
    .del_key = ieee80211_del_key,
    .get_key = ieee80211_get_key,
    .set_default_key = ieee80211_config_default_key,
    .set_default_mgmt_key = ieee80211_config_default_mgmt_key,
    .add_beacon = ieee80211_add_beacon,
    .set_beacon = ieee80211_set_beacon,
    .del_beacon = ieee80211_del_beacon,
    .add_station = ieee80211_add_station,
    .del_station = ieee80211_del_station,
    .change_station = ieee80211_change_station,
    .get_station = ieee80211_get_station,
    .dump_station = ieee80211_dump_station,
    .dump_survey = ieee80211_dump_survey,
#ifdef CONFIG_MAC80211_MESH
    .add_mpath = ieee80211_add_mpath,
    .del_mpath = ieee80211_del_mpath,
    .change_mpath = ieee80211_change_mpath,
    .get_mpath = ieee80211_get_mpath,
    .dump_mpath = ieee80211_dump_mpath,
    .update_mesh_config = ieee80211_update_mesh_config,
    .get_mesh_config = ieee80211_get_mesh_config,
    .join_mesh = ieee80211_join_mesh,
    .leave_mesh = ieee80211_leave_mesh,
#endif
    .change_bss = ieee80211_change_bss,
    .set_txq_params = ieee80211_set_txq_params,
    .set_channel = ieee80211_set_channel,
    .suspend = ieee80211_suspend,
    .resume = ieee80211_resume,
    .scan = ieee80211_scan,
    .sched_scan_start = ieee80211_sched_scan_start,
    .sched_scan_stop = ieee80211_sched_scan_stop,
    .auth = ieee80211_auth,
    .assoc = ieee80211_assoc,
    .deauth = ieee80211_deauth,
    .disassoc = ieee80211_disassoc,
    .join_ibss = ieee80211_join_ibss,
    .leave_ibss = ieee80211_leave_ibss,
    .set_wiphy_params = ieee80211_set_wiphy_params,
    .set_tx_power = ieee80211_set_tx_power,
    .get_tx_power = ieee80211_get_tx_power,
    .set_wds_peer = ieee80211_set_wds_peer,
    .rfkill_poll = ieee80211_rfkill_poll,
    CFG80211_TESTMODE_CMD(ieee80211_testmode_cmd)
    .set_power_mgmt = ieee80211_set_power_mgmt,
    .set_bitrate_mask = ieee80211_set_bitrate_mask,
    .remain_on_channel = ieee80211_remain_on_channel,
    .cancel_remain_on_channel = ieee80211_cancel_remain_on_channel,
    .mgmt_tx = ieee80211_mgmt_tx,
    .mgmt_tx_cancel_wait = ieee80211_mgmt_tx_cancel_wait,
    .set_cqm_rssi_config = ieee80211_set_cqm_rssi_config,
    .mgmt_frame_register = ieee80211_mgmt_frame_register,
    .set_antenna = ieee80211_set_antenna,
    .get_antenna = ieee80211_get_antenna,
    .set_ringparam = ieee80211_set_ringparam,
    .get_ringparam = ieee80211_get_ringparam,
}

3.3 struct iw_handler_def  實例 cfg80211_wext_handler(wireless實現)

      cfg80211_wext_handler實現了wext要求的ioctl操作，將通過net_device->wireless_handlers->standard[ioctl cmd- SIOCIWFIRST]來進行調用。在net/wireless/wext-compat.c中的定義如下所示：

static const iw_handler cfg80211_handlers[] = {
    [IW_IOCTL_IDX(SIOCGIWNAME)] = (iw_handler) cfg80211_wext_giwname,
    [IW_IOCTL_IDX(SIOCSIWFREQ)] = (iw_handler) cfg80211_wext_siwfreq,
    [IW_IOCTL_IDX(SIOCGIWFREQ)] = (iw_handler) cfg80211_wext_giwfreq,
    [IW_IOCTL_IDX(SIOCSIWMODE)] = (iw_handler) cfg80211_wext_siwmode,
    [IW_IOCTL_IDX(SIOCGIWMODE)] = (iw_handler) cfg80211_wext_giwmode,
    [IW_IOCTL_IDX(SIOCGIWRANGE)]    = (iw_handler) cfg80211_wext_giwrange,
    [IW_IOCTL_IDX(SIOCSIWAP)]   = (iw_handler) cfg80211_wext_siwap,
    [IW_IOCTL_IDX(SIOCGIWAP)]   = (iw_handler) cfg80211_wext_giwap,
    [IW_IOCTL_IDX(SIOCSIWMLME)] = (iw_handler) cfg80211_wext_siwmlme,
    [IW_IOCTL_IDX(SIOCSIWSCAN)] = (iw_handler) cfg80211_wext_siwscan,
    [IW_IOCTL_IDX(SIOCGIWSCAN)] = (iw_handler) cfg80211_wext_giwscan,
    [IW_IOCTL_IDX(SIOCSIWESSID)]    = (iw_handler) cfg80211_wext_siwessid,
    [IW_IOCTL_IDX(SIOCGIWESSID)]    = (iw_handler) cfg80211_wext_giwessid,
    [IW_IOCTL_IDX(SIOCSIWRATE)] = (iw_handler) cfg80211_wext_siwrate,
    [IW_IOCTL_IDX(SIOCGIWRATE)] = (iw_handler) cfg80211_wext_giwrate,
    [IW_IOCTL_IDX(SIOCSIWRTS)]  = (iw_handler) cfg80211_wext_siwrts,
    [IW_IOCTL_IDX(SIOCGIWRTS)]  = (iw_handler) cfg80211_wext_giwrts,
    [IW_IOCTL_IDX(SIOCSIWFRAG)] = (iw_handler) cfg80211_wext_siwfrag,
    [IW_IOCTL_IDX(SIOCGIWFRAG)] = (iw_handler) cfg80211_wext_giwfrag,
    [IW_IOCTL_IDX(SIOCSIWTXPOW)]    = (iw_handler) cfg80211_wext_siwtxpower,
    [IW_IOCTL_IDX(SIOCGIWTXPOW)]    = (iw_handler) cfg80211_wext_giwtxpower,
    [IW_IOCTL_IDX(SIOCSIWRETRY)]    = (iw_handler) cfg80211_wext_siwretry,
    [IW_IOCTL_IDX(SIOCGIWRETRY)]    = (iw_handler) cfg80211_wext_giwretry,
    [IW_IOCTL_IDX(SIOCSIWENCODE)]   = (iw_handler) cfg80211_wext_siwencode,
    [IW_IOCTL_IDX(SIOCGIWENCODE)]   = (iw_handler) cfg80211_wext_giwencode,
    [IW_IOCTL_IDX(SIOCSIWPOWER)]    = (iw_handler) cfg80211_wext_siwpower,
    [IW_IOCTL_IDX(SIOCGIWPOWER)]    = (iw_handler) cfg80211_wext_giwpower,
    [IW_IOCTL_IDX(SIOCSIWGENIE)]    = (iw_handler) cfg80211_wext_siwgenie,
    [IW_IOCTL_IDX(SIOCSIWAUTH)] = (iw_handler) cfg80211_wext_siwauth,
    [IW_IOCTL_IDX(SIOCGIWAUTH)] = (iw_handler) cfg80211_wext_giwauth,
    [IW_IOCTL_IDX(SIOCSIWENCODEEXT)]= (iw_handler) cfg80211_wext_siwencodeext,
    [IW_IOCTL_IDX(SIOCSIWPMKSA)]    = (iw_handler) cfg80211_wext_siwpmksa,
  [IW_IOCTL_IDX(SIOCSIWPRIV)] = (iw_handler)cfg80211_wext_setpriv
};

const struct iw_handler_def cfg80211_wext_handler = {
    .num_standard       = ARRAY_SIZE(cfg80211_handlers),
    .standard       = cfg80211_handlers,
    .get_wireless_stats = cfg80211_wireless_stats,
}

4. 創建並註冊net_device

             當執行mac80211_config_ops-> ieee80211_add_iface時，它將創建net_device和對應的ieee80211_sub_if_data, 然後主要做了以下幾件事：

        1) 把net_device對應的名字增加到/sys/class/net/目錄下   

        2) 把新創建的net_device插入到init_net->dev_base_head中

        3) 通知上層協議，有一個新的net_device出現了，大家可以使用它了

        4) 把新創建的ieee80211_sub_if_data增加到ieee80211_local的interfaces列表中        

        其流程如下圖所示：

        mac80211中定義的net_device_ops ieee80211_dataif_ops，以下這些方法，都有一個struct net_device參數。其具體定義如下：   

static const struct net_device_ops ieee80211_dataif_ops = {
    .ndo_open       = ieee80211_open,              // net_device變換到 UP 時被調用
    .ndo_stop       = ieee80211_stop,              // net_device變換到 Down 時被調用
    .ndo_uninit     = ieee80211_teardown_sdata,    // 取消註冊或註冊失敗時調用
    .ndo_start_xmit     = ieee80211_subif_start_xmit,  // 需要發送包時被調用
    .ndo_set_multicast_list = ieee80211_set_multicast_list,// 多播地址列表變化時被調用
    .ndo_change_mtu     = ieee80211_change_mtu,        // 當用戶想改變一個設備的MTU時被調用
    .ndo_set_mac_address    = ieee80211_change_mac,        // mac地址需要改變時被調用
    .ndo_select_queue   = ieee80211_netdev_select_queue, //當net_device支持多個發送隊列時，用來決定使用哪個隊列
};

  mac80211中初始化net_device->netdev_ops:

static void ieee80211_if_setup(struct net_device *dev)
{
    ether_setup(dev);
    dev->priv_flags &= ~IFF_TX_SKB_SHARING;
    dev->netdev_ops = &ieee80211_dataif_ops;
    dev->destructor = free_netdev;
}

5. 數據接收(Data RX)流程

   數據接收流程如下圖所示：

IP層與TCP/UDP層接口定義如下：

static const struct net_protocol tcp_protocol = {
    .handler =  tcp_v4_rcv,
    .err_handler =  tcp_v4_err,
    .gso_send_check = tcp_v4_gso_send_check,
    .gso_segment =  tcp_tso_segment,
    .gro_receive =  tcp4_gro_receive,
    .gro_complete = tcp4_gro_complete,
    .no_policy =    1,
    .netns_ok = 1,
};

static const struct net_protocol udp_protocol = {
    .handler =  udp_rcv,
    .err_handler =  udp_err,
    .gso_send_check = udp4_ufo_send_check,
    .gso_segment = udp4_ufo_fragment,
    .no_policy =    1,
    .netns_ok = 1,
};

static const struct net_protocol icmp_protocol = {
    .handler =  icmp_rcv,
    .err_handler =  ping_err,
    .no_policy =    1,
    .netns_ok = 1,
};

IP層與net/core層接口定義如下：

static struct packet_type ip_packet_type __read_mostly = {
    .type = cpu_to_be16(ETH_P_IP),
    .func = ip_rcv,
    .gso_send_check = inet_gso_send_check,
    .gso_segment = inet_gso_segment,
    .gro_receive = inet_gro_receive,
    .gro_complete = inet_gro_complete,
};

接收下半部stack如下所示：

[  336.646628] [<c07d8b24>] (tcp_rcv_established+0x648/0x9b0) from [<c07e04cc>] (tcp_v4_do_rcv+0x74/0x2a8)
[  336.646661] [<c07e04cc>] (tcp_v4_do_rcv+0x74/0x2a8) from [<c07e0c40>] (tcp_v4_rcv+0x540/0x908)
[  336.646678] [<c07e0c40>] (tcp_v4_rcv+0x540/0x908) from [<c07c23d4>] (ip_local_deliver_finish+0x158/0x318)
[  336.646694] [<c07c23d4>] (ip_local_deliver_finish+0x158/0x318) from [<c07c1e44>] (ip_rcv_finish+0x420/0x440)
[  336.646715] [<c07c1e44>] (ip_rcv_finish+0x420/0x440) from [<c0772dcc>] (__netif_receive_skb+0x4d0/0x534)
[  336.646730] [<c0772dcc>] (__netif_receive_skb+0x4d0/0x534) from [<c0774434>] (netif_receive_skb+0x9c/0xb4)
[  336.646752] [<c0774434>] (netif_receive_skb+0x9c/0xb4) from [<c08b8e6c>] (ieee80211_deliver_skb+0x134/0x164)
[  336.646769] [<c08b8e6c>] (ieee80211_deliver_skb+0x134/0x164) from [<c08b9ed8>] (ieee80211_rx_handlers+0x103c/0x1978)
[  336.646785] [<c08b9ed8>] (ieee80211_rx_handlers+0x103c/0x1978) from [<c08baf10>] (ieee80211_prepare_and_rx_handle+0x6fc/0x788)
[  336.646802] [<c08baf10>] (ieee80211_prepare_and_rx_handle+0x6fc/0x788) from [<c08bb920>] (ieee80211_rx+0x908/0x988)
[  336.646819] [<c08bb920>] (ieee80211_rx+0x908/0x988) from [<c068a578>] (ath9k_rx_tasklet+0x4e4/0x54c)
[  336.646835] [<c068a578>] (ath9k_rx_tasklet+0x4e4/0x54c) from [<c0467d98>] (tasklet_action+0xa8/0x14c)
[  336.646850] [<c0467d98>] (tasklet_action+0xa8/0x14c) from [<c0468144>] (__do_softirq+0x88/0x158)
[  336.646863] [<c0468144>] (__do_softirq+0x88/0x158) from [<c0468414>] (irq_exit+0x48/0xac)
[  336.646882] [<c0468414>] (irq_exit+0x48/0xac) from [<c04313c0>] (do_local_timer+0x50/0x80)
[  336.646898] [<c04313c0>] (do_local_timer+0x50/0x80) from [<c0436708>] (__irq_svc+0x48/0xe0)

6. 數據發送(Data TX)流珵

   數據發送流程如下圖所示：

上半部分涉及到的相關代碼如下所示（以上流程主要通過dump_stack獲取）：

     net/socket.c
     net/ipv4/af_net.c
     net/ipv4/tcp.c
     net/ipv4/tcp_output.c
     net/ipv4/ip_output.c
     net/core/neighbour.c
     net/core/dev.c

7. INET初始化

    INET爲Linux OS實現了TCP/IP協議集，它使用BSD Socket接口作爲與User通訊的方式。其初始化代碼如下所示：

    代碼位於：net/ipv4/af_inet.c。

static int __init inet_init(void)
{
    struct sk_buff *dummy_skb;
    struct inet_protosw *q;
    struct list_head *r;
    int rc = -EINVAL;

    BUILD_BUG_ON(sizeof(struct inet_skb_parm) > sizeof(dummy_skb->cb));

    sysctl_local_reserved_ports = kzalloc(65536 / 8, GFP_KERNEL);
    if (!sysctl_local_reserved_ports)
        goto out;

    rc = proto_register(&tcp_prot, 1);
    if (rc)
        goto out_free_reserved_ports;

    rc = proto_register(&udp_prot, 1);
    if (rc)
        goto out_unregister_tcp_proto;

    rc = proto_register(&raw_prot, 1);
    if (rc)
        goto out_unregister_udp_proto;

    rc = proto_register(&ping_prot, 1);
    if (rc)
        goto out_unregister_raw_proto;

    /*
     *  Tell SOCKET that we are alive...
     */

    (void)sock_register(&inet_family_ops);

#ifdef CONFIG_SYSCTL
    ip_static_sysctl_init();
#endif

    /*
     *  Add all the base protocols.
     */

    if (inet_add_protocol(&icmp_protocol, IPPROTO_ICMP) < 0)
        printk(KERN_CRIT "inet_init: Cannot add ICMP protocol\n");
    if (inet_add_protocol(&udp_protocol, IPPROTO_UDP) < 0)
        printk(KERN_CRIT "inet_init: Cannot add UDP protocol\n");
    if (inet_add_protocol(&tcp_protocol, IPPROTO_TCP) < 0)
        printk(KERN_CRIT "inet_init: Cannot add TCP protocol\n");
#ifdef CONFIG_IP_MULTICAST
    if (inet_add_protocol(&igmp_protocol, IPPROTO_IGMP) < 0)
        printk(KERN_CRIT "inet_init: Cannot add IGMP protocol\n");
#endif

    /* Register the socket-side information for inet_create. */
    for (r = &inetsw[0]; r < &inetsw[SOCK_MAX]; ++r)
        INIT_LIST_HEAD(r);

    for (q = inetsw_array; q < &inetsw_array[INETSW_ARRAY_LEN]; ++q)
        inet_register_protosw(q);

    /*
     *  Set the ARP module up
     */

    arp_init();

    /*
     *  Set the IP module up
     */

    ip_init();

    tcp_v4_init();

    /* Setup TCP slab cache for open requests. */
    tcp_init();

    /* Setup UDP memory threshold */
    udp_init();

    /* Add UDP-Lite (RFC 3828) */
    udplite4_register();

    ping_init();

    /*
     *  Set the ICMP layer up
     */

    if (icmp_init() < 0)
        panic("Failed to create the ICMP control socket.\n");

    /*
     *  Initialise the multicast router
     */
#if defined(CONFIG_IP_MROUTE)
    if (ip_mr_init())
        printk(KERN_CRIT "inet_init: Cannot init ipv4 mroute\n");
#endif
    /*
     *  Initialise per-cpu ipv4 mibs
     */

    if (init_ipv4_mibs())
        printk(KERN_CRIT "inet_init: Cannot init ipv4 mibs\n");

    ipv4_proc_init();

    ipfrag_init();

    dev_add_pack(&ip_packet_type);

    rc = 0;
out:
    return rc;
out_unregister_raw_proto:
    proto_unregister(&raw_prot);
out_unregister_udp_proto:
    proto_unregister(&udp_prot);
out_unregister_tcp_proto:
    proto_unregister(&tcp_prot);
out_free_reserved_ports:
    kfree(sysctl_local_reserved_ports);
    goto out;
}