hostapd wpa_supplicant madwifi详细分析（四）——interface的初始化

        前面讲了的初始，这一节将介绍interface的初始化

        关于interface这个词在这里具体指的是什么，开始的时候自己也很模糊，经过多次询问和验证，个人将这个interface理解为无线网卡物理口，即我们用ifconfig打印出的wifi0和wifi1这样的接口。我们知道，hostapd的一个主要功能是将一个无线网卡切换成ap模式，让它以server端的角色运行，能够让其他无线设备连接上来。现在的路由器一般都支持2.4G和5G两种无线频段，所以在硬件上自然会有两块无线网卡，那么在这两块无线网卡都运行的时候，能够在ifconfig中看到wifi0和wifi1的状态都是up的，使用ps -w | grep hostapd 也能够查看到，hostapd到底使用的是哪个网卡的配置文件，到底启动了那块网卡。

       这里需要辨别一下物理网卡口和空中接口的区别，空中接口多以ath0,ath1等字样命名，它们作为无线用户的接入点，可以创建多个，甚至多于网卡的数量，比如在路由器启动guest network功能的时候，用iwconfig命令可以查看到4个空中接口，这些都可以作为用户的接入点，他们主要是需要使用不同的用户名和密码进行认证，但最终数据包的处理还是经过实际的两块网卡进行的。

       下面说一下，程序时怎么初始化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;}}

这个循环控制变量i的值是由interfaces.count = argc - optind 获得的，argc的值是所有传入参数的个数加一，optind的值是选项的偏移数，初始值是1.  比如

hostapd -B -e /etc/entropy  /etc/ath1.conf  /etc/ath0.conf

以这样的参数运行hostapd时，argc=6   optind=4，那么count的值将等于2,其实也可以这样理解：argc - optind就是非选项参数的个数，比如上面 -B是不带参数的选项，-e是带一个参数/etc/entropy的选项，那么剩下的/etc/ath1.conf   /etc/ath0.conf不是某个选项的参数，所以不需要经过getopt类似函数的处理，不会使optind的值加一，所以差计算后他们的个数是2.

         接下来好好说一下hostapd_interface_init这个函数。

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 对interface的操作函数以及标示变量的封装

struct hostapd_iface {struct hapd_interfaces *interfaces; void *owner;   char *config_fname; // 这里存放配置文件路径和文件名struct hostapd_config *conf;   //将配置文件中的信息读取后，将存放在这个结构体中char phy[16]; /* Name of the PHY (radio) */     //无线网卡芯片名enum hostapd_iface_state {         //描述接口状态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;       //基础服务集合个数struct hostapd_data **bss;  //存放bss数据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_ACSunsigned int acs_num_completed_scans;#endif /* CONFIG_ACS */void (*scan_cb)(struct hostapd_iface *iface);int num_ht40_scan_tries;

2. hostapd_init()函数

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;         //这个结构体很重要，存放了数据以及一些报文相关的操作和信息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_readconf = 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内以该interface的配置文件作为参数调用hostapd_config_read。并将读取到的配置信息赋给成员变量struct hostapd_config *conf.
根据配置文件中bss的配置个数conf->num_bss的值通过调用hostapd_alloc_bss_data分配空间及相关设置，并对hapd_iface->bss[i]进行赋值，

其中hostapd_alloc_bss_data的定义为
static struct hostapd_data *hostapd_alloc_bss_data(struct hostapd_iface *hapd_iface, struct hostapd_config *conf, struct hostapd_bss_config *bss)

三个参数分别为本interface信息，本interface的配置信息，本interface配置信息中第i个bss的配置部分。
其中代码 (struct hostapd_data *hapd)
 hapd->iconf = conf;
 hapd->conf = bss;
 hapd->iface = hapd_iface;
使得hostapd_data中均有指向这几个配置的指针了。
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之间是相互联系的。