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

柔光的暖阳◎ 2022-08-06 04:22 330阅读 0赞

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_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_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。