（四）interface的初始化 · 無線局域網開發

前面講了的初始，這一節將介紹interface的初始化關于interface這個詞在這里具體指的是什么，開始的時候自己也很模糊，經過多次詢問和驗證，個人將這個interface理解為無線網卡物理口，即我們用ifconfig打印出的wifi0和wifi1這樣的接口。我們知道，hostapd的一個主要功能是將一個無線網卡切換成ap模式，讓它以server端的角色運行，能夠讓其他無線設備連接上來。現在的路由器一般都支持2.4G和5G兩種無線頻段，所以在硬件上自然會有兩塊無線網卡，那么在這兩塊無線網卡都運行的時候，能夠在ifconfig中看到wifi0和wifi1的狀態都是up的，使用ps -w | grep hostapd 也能夠查看到，hostapd到底使用的是哪個網卡的配置文件，到底啟動了那塊網卡。這里需要辨別一下物理網卡口和空中接口的區別，空中接口多以ath0,ath1等字樣命名，它們作為無線用戶的接入點，可以創建多個，甚至多于網卡的數量，比如在路由器啟動guest network功能的時候，用iwconfig命令可以查看到4個空中接口，這些都可以作為用戶的接入點，他們主要是需要使用不同的用戶名和密碼進行認證，但最終數據包的處理還是經過實際的兩塊網卡進行的。下面說一下，程序時怎么初始化interface的。 ~~~ for (i = 0; i < interfaces.count; i++) { interfaces.iface[i] = hostapd_interface_init(&interfaces, argv[optind + i], debug); if (!interfaces.iface[i]) { wpa_printf(MSG_ERROR, "Failed to initialize interface"); goto out; } } ~~~ 這個循環控制變量i的值是由interfaces.count = argc - optind 獲得的，argc的值是所有傳入參數的個數加一，optind的值是選項的偏移數，初始值是1.? 比如 hostapd -B -e /etc/entropy? /etc/ath1.conf? /etc/ath0.conf 以這樣的參數運行hostapd時，argc=6?? optind=4，那么count的值將等于2,其實也可以這樣理解：argc - optind就是非選項參數的個數，比如上面 -B是不帶參數的選項，-e是帶一個參數/etc/entropy的選項，那么剩下的/etc/ath1.conf?? /etc/ath0.conf不是某個選項的參數，所以不需要經過getopt類似函數的處理，不會使optind的值加一，所以差計算后他們的個數是2. 接下來好好說一下hostapd_interface_init這個函數。 ~~~ static struct hostapd_iface * hostapd_interface_init(struct hapd_interfaces *interfaces, const char *config_fname, int debug) { struct hostapd_iface *iface; int k; wpa_printf(MSG_ERROR, "Configuration file: %s", config_fname); iface = hostapd_init(interfaces, config_fname); if (!iface) return NULL; iface->interfaces = interfaces; for (k = 0; k < debug; k++) { if (iface->bss[0]->conf->logger_stdout_level > 0) iface->bss[0]->conf->logger_stdout_level--; } if (iface->conf->bss[0]->iface[0] == '\0' && !hostapd_drv_none(iface->bss[0])) { wpa_printf(MSG_ERROR, "Interface name not specified in %s", config_fname); hostapd_interface_deinit_free(iface); return NULL; } return iface; } ~~~ 1.先看struct hostapd_iface 對interface的操作函數以及標示變量的封裝 ~~~ struct hostapd_iface { struct hapd_interfaces *interfaces; void *owner; char *config_fname; // 這里存放配置文件路徑和文件名 struct hostapd_config *conf; //將配置文件中的信息讀取后，將存放在這個結構體中 char phy[16]; /* Name of the PHY (radio) */ //無線網卡芯片名 enum hostapd_iface_state { //描述接口狀態 HAPD_IFACE_UNINITIALIZED, HAPD_IFACE_DISABLED, HAPD_IFACE_COUNTRY_UPDATE, HAPD_IFACE_ACS, HAPD_IFACE_HT_SCAN, HAPD_IFACE_DFS, HAPD_IFACE_ENABLED } state; size_t num_bss; //基礎服務集合個數 struct hostapd_data **bss; //存放bss數據 unsigned int wait_channel_update:1; unsigned int cac_started:1; /* * When set, indicates that the driver will handle the AP * teardown: delete global keys, station keys, and stations. */ unsigned int driver_ap_teardown:1; int num_ap; /* number of entries in ap_list */ struct ap_info *ap_list; /* AP info list head */ struct ap_info *ap_hash[STA_HASH_SIZE]; unsigned int drv_flags; /* * A bitmap of supported protocols for probe response offload. See * struct wpa_driver_capa in driver.h */ unsigned int probe_resp_offloads; /* extended capabilities supported by the driver */ const u8 *extended_capa, *extended_capa_mask; unsigned int extended_capa_len; unsigned int drv_max_acl_mac_addrs; struct hostapd_hw_modes *hw_features; int num_hw_features; struct hostapd_hw_modes *current_mode; /* Rates that are currently used (i.e., filtered copy of * current_mode->channels */ int num_rates; struct hostapd_rate_data *current_rates; int *basic_rates; int freq; u16 hw_flags; /* Number of associated Non-ERP stations (i.e., stations using 802.11b * in 802.11g BSS) */ int num_sta_non_erp; /* Number of associated stations that do not support Short Slot Time */ int num_sta_no_short_slot_time; /* Number of associated stations that do not support Short Preamble */ int num_sta_no_short_preamble; int olbc; /* Overlapping Legacy BSS Condition */ /* Number of HT associated stations that do not support greenfield */ int num_sta_ht_no_gf; /* Number of associated non-HT stations */ int num_sta_no_ht; /* Number of HT associated stations 20 MHz */ int num_sta_ht_20mhz; /* Number of HT40 intolerant stations */ int num_sta_ht40_intolerant; /* Overlapping BSS information */ int olbc_ht; u16 ht_op_mode; /* surveying helpers */ /* number of channels surveyed */ unsigned int chans_surveyed; /* lowest observed noise floor in dBm */ s8 lowest_nf; unsigned int dfs_cac_ms; struct os_reltime dfs_cac_start; /* Latched with the actual secondary channel information and will be * used while juggling between HT20 and HT40 modes. */ int secondary_ch; #ifdef CONFIG_ACS unsigned int acs_num_completed_scans; #endif /* CONFIG_ACS */ void (*scan_cb)(struct hostapd_iface *iface); int num_ht40_scan_tries; ~~~ 2.hostapd_init()函數 ~~~ struct hostapd_iface * hostapd_init(struct hapd_interfaces *interfaces, const char *config_file) { struct hostapd_iface *hapd_iface = NULL; struct hostapd_config *conf = NULL; struct hostapd_data *hapd; //這個結構體很重要，存放了數據以及一些報文相關的操作和信息 size_t i; hapd_iface = os_zalloc(sizeof(*hapd_iface)); if (hapd_iface == NULL) goto fail; hapd_iface->config_fname = os_strdup(config_file); if (hapd_iface->config_fname == NULL) goto fail; <pre name="code" class="cpp"> interfaces->config_read_cb=hostapd_config_read conf = interfaces->config_read_cb(hapd_iface->config_fname); if (conf == NULL) goto fail; hapd_iface->conf = conf; hapd_iface->num_bss = conf->num_bss; hapd_iface->bss = os_calloc(conf->num_bss, sizeof(struct hostapd_data *)); if (hapd_iface->bss == NULL) goto fail; for (i = 0; i < conf->num_bss; i++) { hapd = hapd_iface->bss[i] = hostapd_alloc_bss_data(hapd_iface, conf, conf->bss[i]); if (hapd == NULL) goto fail; hapd->msg_ctx = hapd; } return hapd_iface; ~~~ hostapd_init內以該interface的配置文件作為參數調用hostapd_config_read。并將讀取到的配置信息賦給成員變量struct hostapd_config *conf. 根據配置文件中bss的配置個數conf->num_bss的值通過調用hostapd_alloc_bss_data分配空間及相關設置，并對hapd_iface->bss[i]進行賦值，其中hostapd_alloc_bss_data的定義為 static struct hostapd_data *hostapd_alloc_bss_data(struct hostapd_iface *hapd_iface, struct hostapd_config *conf, struct hostapd_bss_config *bss) 三個參數分別為本interface信息，本interface的配置信息，本interface配置信息中第i個bss的配置部分。其中代碼 (struct hostapd_data *hapd) hapd->iconf = conf; hapd->conf = bss; hapd->iface = hapd_iface; 使得hostapd_data中均有指向這幾個配置的指針了。既有: hapd_iface->bss[i]->iconf == hapd_iface->conf hapd_iface->bss[i]->conf == &hapd_iface->conf->bss[i] hapd_iface->bss[i]->iface == hapd_iface 所以struct hostapd_data,? struct hostapd_iface, struct hostapd_config, struct hostapd_bss_config之間是相互聯系的。