wpa_supplicant与用户态程序的交互分析

1 wpa_supplicant与用户态程序wpa_cli的交互过程

1.1 交互接口类型

wpa_supplicant与用户态程序交互的主要接口包括以下几种：

1）命令行界面：通过命令行工具 wpa_cli 可以与 wpa_supplicant 进行交互。wpa_cli 允许用户执行各种 wpa_supplicant 操作，如配置网络、扫描网络、断开连接等。用户可以通过命令行输入命令，然后 wpa_cli 会将命令传递给 wpa_supplicant，并返回执行结果。
2）控制接口文件：wpa_supplicant 会创建一个控制接口文件，通常位于 /var/run/wpa_supplicant/ 目录下，以与外部程序进行通信。通过控制接口文件，外部程序可以向 wpa_supplicant 发送命令，以配置和管理无线网络连接。这通常涉及到读写控制接口文件中的数据，以执行各种操作。
3）D-Bus 接口：wpa_supplicant 也提供了一个 D-Bus 接口，允许外部程序使用 D-Bus 协议与其通信。通过 D-Bus 接口，外部程序可以查询和配置 wpa_supplicant 的状态、网络配置等信息。D-Bus 是一种通用的进程间通信机制，在许多Linux系统上都受支持。
4）自定义接口：有些外部程序可能会使用 wpa_supplicant 提供的自定义接口，通过编程方式与其交互。

用户态程序和wpa_supplicant两个进程之间通信的方式一般为unix socket

wpa_cli就是一个用户态程序，本文以wpa_cli为代表分析wpa_supplicant与用户态之间的交互

1.2 交互命令和日志

首先，执行wpa_supplicant命令

sudo ./wpa_supplicant -i wlan0 -D nl80211 -c /etc/wpa_supplicant/wpa_supplicant.conf

该命令会调用wpa_supplicant/main.c文件中的main()主函数

然后，执行wpa_cli命令

sudo ./wpa_cli -i wlan0 scan

该命令会调用wpa_supplicant/wpa_cli.c文件中的main()主函数

在wpa_cli端发出扫描命令后，wpa_supplicant端接收到来自wpa_cli的消息，其处理日志如下

wlan0: Control interface command 'SCAN'
wlan0: Setting scan request: 0.000000 sec
wlan0: Starting AP scan for wildcard SSID
WPS: Building WPS IE for Probe Request
WPS:  * Version (hardcoded 0x10)
WPS:  * Request Type
WPS:  * Config Methods (3108)
WPS:  * UUID-E
WPS:  * Primary Device Type
WPS:  * RF Bands (1)
WPS:  * Association State
WPS:  * Configuration Error (0)
WPS:  * Device Password ID (0)
WPS:  * Manufacturer
WPS:  * Model Name
WPS:  * Model Number
WPS:  * Device Name
WPS:  * Version2 (0x20)
P2P: * P2P IE header
P2P: * Capability dev=25 group=00
P2P: * Listen Channel: Regulatory Class 81 Channel 1
wlan0: Add radio work 'scan'@0x5558d881f330
wlan0: First radio work item in the queue - schedule start immediately
wlan0: Starting radio work 'scan'@0x5558d881f330 after 0.000006 second wait
wlan0: nl80211: scan request
Scan requested (ret=0) - scan timeout 30 seconds
nl80211: Drv Event 33 (NL80211_CMD_TRIGGER_SCAN) received for wlan0
wlan0: nl80211: Scan trigger
wlan0: Event SCAN_STARTED (47) received
wlan0: Own scan request started a scan in 0.000000 seconds
RTM_NEWLINK: ifi_index=4 ifname=wlan0 wext ifi_family=0 ifi_flags=0x11043 ([UP][RUNNING][LOWER_UP])
nl80211: Drv Event 34 (NL80211_CMD_NEW_SCAN_RESULTS) received for wlan0
wlan0: nl80211: New scan results available
nl80211: Scan probed for SSID ''
nl80211: Scan included frequencies: 2412 2417 2422 2427 2432 2437 2442 2447 2452 2457 2462 2467 2472
wlan0: Event SCAN_RESULTS (3) received
wlan0: Scan completed in 11.500205 seconds
nl80211: Received scan results (35 BSSes)
nl80211: Scan results indicate BSS status with 48:2f:6b:2a:07:80 as associated
wlan0: BSS: Start scan result update 3
wlan0: BSS: Add new id 56 BSSID 7c:10:c9:b4:d0:48 SSID 'ASUS_2G' freq 2412
wlan0: BSS: Add new id 57 BSSID 9c:8c:d8:00:a8:e0 SSID 'i-amlogic' freq 2412
wlan0: BSS: Add new id 58 BSSID 9a:00:74:f7:03:b6 SSID 'ChinaNet-UuxC' freq 2412
wlan0: BSS: Add new id 59 BSSID 9c:8c:d8:00:a8:e1 SSID 'sunshine' freq 2412
wlan0: BSS: Add new id 60 BSSID 9c:8c:d8:00:a8:e2 SSID 'galaxy' freq 2412
wlan0: BSS: Add new id 61 BSSID 48:5b:ea:eb:9d:30 SSID 'ChinaNet-DFrr' freq 2432
wlan0: BSS: Add new id 62 BSSID 9c:8c:d8:fe:de:60 SSID 'i-amlogic' freq 2462
BSS: last_scan_res_used=35/64
wlan0: New scan results available (own=1 ext=0)
WPS: AP 48:5b:ea:eb:9d:30 type 0 added
WPS: AP[0] b8:3a:08:17:7f:71 type=0 tries=0 last_attempt=-1 sec ago bssid_ignore=0
WPS: AP[1] 92:a5:af:5e:27:dc type=0 tries=0 last_attempt=-1 sec ago bssid_ignore=0
WPS: AP[2] 58:48:49:0b:b8:63 type=0 tries=0 last_attempt=-1 sec ago bssid_ignore=0
WPS: AP[3] 50:2b:73:c9:11:29 type=0 tries=0 last_attempt=-1 sec ago bssid_ignore=0
WPS: AP[4] 48:5b:ea:eb:a1:2c type=0 tries=0 last_attempt=-1 sec ago bssid_ignore=0
WPS: AP[5] 9c:74:6f:40:a0:40 type=0 tries=0 last_attempt=-1 sec ago bssid_ignore=0
WPS: AP[6] a2:cd:b6:00:c9:b9 type=0 tries=0 last_attempt=-1 sec ago bssid_ignore=0
WPS: AP[7] 14:f5:09:dd:64:f6 type=0 tries=0 last_attempt=-1 sec ago bssid_ignore=0
WPS: AP[8] 48:5b:ea:eb:9d:30 type=0 tries=0 last_attempt=-1 sec ago bssid_ignore=0
wlan0: Radio work 'scan'@0x5558d881f330 done in 11.507001 seconds
wlan0: radio_work_free('scan'@0x5558d881f330): num_active_works --> 0
wlan0: Scan results matching the currently selected network
wlan0: 6: 48:2f:6b:2a:d9:40 freq=2462 level=-56 snr=33 est_throughput=65000
wlan0: 9: 48:2f:6b:2a:07:80 freq=2462 level=-58 snr=31 est_throughput=65000
wlan0: 13: 9c:8c:d8:00:a8:e0 freq=2412 level=-62 snr=27 est_throughput=65000
wlan0: 29: 9c:8c:d8:fe:3f:80 freq=2462 level=-80 snr=9 est_throughput=19500
wlan0: 31: 9c:8c:d8:fe:de:60 freq=2462 level=-88 snr=1 est_throughput=3250
wlan0: Selecting BSS from priority group 0
wlan0: 0: 22:f2:2c:43:84:a1 ssid='' wpa_ie_len=22 rsn_ie_len=20 caps=0x431 level=-54 freq=2462
wlan0:    skip - SSID not known
wlan0: 1: 18:f2:2c:43:84:a1 ssid='TV-SE' wpa_ie_len=22 rsn_ie_len=20 caps=0x1431 level=-56 freq=2462
wlan0:    skip - SSID mismatch
wlan0: 2: f6:84:8d:21:4c:3b ssid='' wpa_ie_len=22 rsn_ie_len=20 caps=0x411 level=-67 freq=2462
wlan0:    skip - SSID not known
wlan0: 3: f4:84:8d:21:4c:3b ssid='QA_2.4G' wpa_ie_len=22 rsn_ie_len=20 caps=0x1411 level=-68 freq=2462
wlan0:    skip - SSID mismatch
wlan0: 4: 7c:10:c9:b4:d0:48 ssid='ASUS_2G' wpa_ie_len=0 rsn_ie_len=20 caps=0x1411 level=-69 freq=2412
wlan0:    skip - SSID mismatch
wlan0: 5: 48:2f:6b:2a:d9:41 ssid='sunshine' wpa_ie_len=0 rsn_ie_len=20 caps=0x431 level=-56 freq=2462
wlan0:    skip - SSID mismatch
wlan0: 6: 48:2f:6b:2a:d9:40 ssid='i-amlogic' wpa_ie_len=0 rsn_ie_len=20 caps=0x431 level=-56 freq=2462
wlan0:    selected based on RSN IE
wlan0:    selected BSS 48:2f:6b:2a:d9:40 ssid='i-amlogic'
wlan0: Considering within-ESS reassociation
wlan0: Current BSS: 48:2f:6b:2a:07:80 freq=2462 level=-58 snr=31 est_throughput=65000
wlan0: Selected BSS: 48:2f:6b:2a:d9:40 freq=2462 level=-56 snr=33 est_throughput=65000
wlan0: Using signal poll values for the current BSS: level=-59 snr=30 est_throughput=65000
wlan0: Skip roam - Current BSS has good SNR (30 > 25)
wlan0: BSS: Remove id 26 BSSID 6c:b1:58:e4:97:0d SSID 'TP-LINK_970D' due to wpa_bss_flush_by_age
wlan0: BSS: Remove id 31 BSSID b8:3a:08:17:7f:71 SSID 'Moonflower' due to wpa_bss_flush_by_age
wlan0: BSS: Remove id 41 BSSID 48:2f:6b:2a:37:80 SSID 'i-amlogic' due to wpa_bss_flush_by_age
wlan0: BSS: Remove id 48 BSSID 9c:54:c2:fb:66:30 SSID 'cyem' due to wpa_bss_flush_by_age
wlan0: BSS: Remove id 52 BSSID 14:f5:09:dd:64:f6 SSID '' due to wpa_bss_flush_by_age

1.3 wpa_cli的main函数

wpa_cli的main函数依次调用了以下子函数

1）调用wpa_cli_open_global_ctrl()函数，用于打开global接口，因为本文执行命令时没有指定-g参数，所以该函数实际没有起到作用
2）wpa_cli_open_connection()函数，用于打开socket连接，修改全局变量ctrl_conn的值，传入该函数的参数即为命令中-i指定的waln0
3）wpa_request()函数，用于向wpa_supplicant发起请求命令，传入该函数的参数即为全局接口ctrl_conn和命令中的scan字符

//wpa_supplicant\wpa_cli.c
int main(int argc, char *argv[])
{int c;int daemonize = 0;int ret = 0;
if (os_program_init())return -1;
for (;;) {c = getopt(argc, argv, "a:Bg:G:hi:p:P:rs:v");if (c < 0)break;switch (c) {case 'i':os_free(ctrl_ifname);ctrl_ifname = os_strdup(optarg);break;}
if (eloop_init())return -1;
if (wpa_cli_open_global_ctrl() < 0)return -1;
eloop_register_signal_terminate(wpa_cli_terminate, NULL);
if (wpa_cli_open_connection(ctrl_ifname, 0) < 0) {fprintf(stderr, "Failed to connect to non-global ""ctrl_ifname: %s  error: %s\n",ctrl_ifname ? ctrl_ifname : "(nil)",strerror(errno));return -1;}ret = wpa_request(ctrl_conn, argc - optind,&argv[optind]);
os_free(ctrl_ifname);eloop_destroy();wpa_cli_cleanup();
return ret;
}

1.3.1 wpa_cli_open_global_ctrl函数

wpa_cli_open_global_ctrl()函数没有输入参数，返回参数为整型变量，返回0表示成功，返回-1表示失败，wpa_cli_open_global_ctrl()函数中继续调用了wpa_ctrl_open2()函数，该函数用于打开wpa_supplicant的控制接口

wpa_ctrl_open2()函数返回一个指向控制接口数据的指针wpa_ctrl，该函数有2个输入参数，如下

第1个输入参数为wpa_supplicant控制接口的unix套接字路径，实际传入的是NULL
第2个输入参数为客户端（wpa_cli）的unix套接字路径，实际传入的是NULL

函数结构如下：

//wpa_supplicant\wpa_cli.c
static struct wpa_ctrl *ctrl_conn;
static const char *global = NULL;//wpa_supplicant\wpa_cli.c
static int wpa_cli_open_global_ctrl(void)
{ctrl_conn = wpa_ctrl_open(global);return 0;
}//src\common\wpa_ctrl.c
struct wpa_ctrl * wpa_ctrl_open(const char *ctrl_path)
{return wpa_ctrl_open2(ctrl_path, NULL);
}//src\common\wpa_ctrl.c
struct wpa_ctrl * wpa_ctrl_open2(const char *ctrl_path, const char *cli_path)
{struct wpa_ctrl *ctrl;if (ctrl_path == NULL)return NULL;
}

因为在命令中没有指定-g参数，所以全局变量global参数默认为NULL

因此传递给函数wpa_ctrl_open2()的参数ctrl_path为NULL，所以实际上该函数返回为NULL，全局变量ctrl_conn也就被设置为NULL

1.3.2 wpa_cli_open_connection函数

wpa_cli_open_connection()函数用于打开和wpa_supplicant的连接，并在函数中改变全局变量ctrl_conn的值，wpa_cli_open_connection()函数返回1个整型变量，成功返回0，失败返回-1，该函数有2个输入参数，如下

传入第1个参数接口名称，实际传入的为命令中-i指定的wlan
传入第2个参数为指定连接的方式或附加方式，实际传入0，表示只建立连接，不附加到接口

函数结构如下：

//wpa_supplicant\wpa_cli.c
#ifndef CONFIG_CTRL_IFACE_DIR
#define CONFIG_CTRL_IFACE_DIR "/var/run/wpa_supplicant"
#endif /* CONFIG_CTRL_IFACE_DIR */
static const char *ctrl_iface_dir = CONFIG_CTRL_IFACE_DIR;
static const char *client_socket_dir = NULL;
static struct wpa_ctrl *ctrl_conn;//wpa_supplicant\wpa_cli.c
static int wpa_cli_open_connection(const char *ifname, int attach)
{char *cfile = NULL;int flen, res;if (ifname == NULL)return -1;if (cfile == NULL) {flen = os_strlen(ctrl_iface_dir) + os_strlen(ifname) + 2;cfile = os_malloc(flen);if (cfile == NULL)return -1;res = os_snprintf(cfile, flen, "%s/%s", ctrl_iface_dir,ifname);if (os_snprintf_error(flen, res)) {os_free(cfile);return -1;}}ctrl_conn = wpa_ctrl_open2(cfile, client_socket_dir);if (ctrl_conn == NULL) {os_free(cfile);return -1;}os_free(cfile);return 0;
}

该函数仍然调用了wpa_ctrl_open2()函数，并将返回的控制接口指针wpa_ctrl赋值给全局变量ctrl_conn

ctrl_conn为全局变量，类型为结构体指针wpa_ctrl

//src\common\wpa_ctrl.c
struct wpa_ctrl {int s;struct sockaddr_un local;struct sockaddr_un dest;
};

wpa_ctrl的接口类型实际有3种，分别为udp、unix、pipe，本文只分析unix

wpa_cli_open_connection()函数调用wpa_ctrl_open2()函数时，与之前的wpa_cli_open_global_ctrl()函数不一样

wpa_ctrl_open2()函数返回1个结构体指针ctrl，该函数有2个输入参数，如下

传入的第1个参数已经是接口的名称/var/run/wpa_supplicant/wlan0，而不是NULL了
传入的第2个参数是client_socket_dir，其初始值依然是NULL

此时的wpa_ctrl_open2函数结构如下：

//src\common\wpa_ctrl.c
#ifndef CONFIG_CTRL_IFACE_CLIENT_DIR
#define CONFIG_CTRL_IFACE_CLIENT_DIR "/tmp"
#endif /* CONFIG_CTRL_IFACE_CLIENT_DIR */
#ifndef CONFIG_CTRL_IFACE_CLIENT_PREFIX
#define CONFIG_CTRL_IFACE_CLIENT_PREFIX "wpa_ctrl_"
#endif /* CONFIG_CTRL_IFACE_CLIENT_PREFIX *///src\common\wpa_ctrl.c
struct wpa_ctrl * wpa_ctrl_open2(const char *ctrl_path, const char *cli_path)
{struct wpa_ctrl *ctrl;static int counter = 0;int ret;size_t res;int tries = 0;int flags;if (ctrl_path == NULL)return NULL;ctrl = os_zalloc(sizeof(*ctrl));if (ctrl == NULL)return NULL;ctrl->s = socket(PF_UNIX, SOCK_DGRAM, 0);if (ctrl->s < 0) {os_free(ctrl);return NULL;}ctrl->local.sun_family = AF_UNIX;counter++;
try_again:ret = os_snprintf(ctrl->local.sun_path,sizeof(ctrl->local.sun_path),CONFIG_CTRL_IFACE_CLIENT_DIR "/"CONFIG_CTRL_IFACE_CLIENT_PREFIX "%d-%d",(int) getpid(), counter);if (os_snprintf_error(sizeof(ctrl->local.sun_path), ret)) {close(ctrl->s);os_free(ctrl);return NULL;}tries++;if (bind(ctrl->s, (struct sockaddr *) &ctrl->local,sizeof(ctrl->local)) < 0) {if (errno == EADDRINUSE && tries < 2) {unlink(ctrl->local.sun_path);goto try_again;}close(ctrl->s);os_free(ctrl);return NULL;}ctrl->dest.sun_family = AF_UNIX;res = os_strlcpy(ctrl->dest.sun_path, ctrl_path, sizeof(ctrl->dest.sun_path));if (res >= sizeof(ctrl->dest.sun_path)) {close(ctrl->s);os_free(ctrl);return NULL;}if (connect(ctrl->s, (struct sockaddr *) &ctrl->dest,sizeof(ctrl->dest)) < 0) {close(ctrl->s);unlink(ctrl->local.sun_path);os_free(ctrl);return NULL;}flags = fcntl(ctrl->s, F_GETFL);if (flags >= 0) {flags |= O_NONBLOCK;if (fcntl(ctrl->s, F_SETFL, flags) < 0) {perror("fcntl(ctrl->s, O_NONBLOCK)");}}return ctrl;
}

对该函数说明如下：

调用socket()为控制接口创建套接字ctrl->s，地址族为PF_UNIX，表示本地unix域套接字，类型为SOCK_DGRAM，表示无连接通信，协议为0，表示自动选择
创建本地套接字的地址族ctrl->local.sun_family为AF_UNIX
创建本地套接字的地址，例如创建路径为/tmp/wpa_ctrl_13152-1，其命名方式为/tmp/wpa_ctrl_进程pid-尝试次数
调用bind()将创建的套接字与本地地址绑定
创建目标套接字的地址族ctrl->dest.sun_family为AF_UNIX
创建目标套接字的地址，例如创建路径为/var/run/wpa_supplicant/wlan0，其命名方式为/var/run/wpa_supplicant/接口名称
调用connect()将本地socket与目标地址连接
通过一系列socket函数实现wpa_cli与wpa_supplicant进行通信，如果出错则会调用close()关闭socket连接
最后通过fcntl()获取套接字ctrl->s的标志位，并将套接字设置为非阻塞模式，以避免在目标程序意外终止时导致程序永远阻塞

整个过程中设置了控制接口的ctrl->s、ctrl->local、ctrl→dest这3个成员的值

//src\common\wpa_ctrl.c
struct wpa_ctrl {int s;  //文件描述符struct sockaddr_un local;  //本地UNIX域套接字的地址信息struct sockaddr_un dest;   //目标UNIX域套接字的地址信息
};

1.3.3 wpa_request函数

在main()函数的最后，调用了wpa_request()函数发送命令

ret = wpa_request(ctrl_conn, argc - optind, &argv[optind]);

argc表示参数的个数，sudo ./wpa_cli -i wlan0 scan 这条命令的参数共有4个（除sudo），所以argc为4

optind表示解析命令行参数的状态，初始值为1，每处理一个参数（-i、wlan0、scan均为参数），optind的值加1，当解析完所有参数时，optind的值为3

&argv[optind]表示最后一个参数的地址，即字符串scan

wpa_request()函数返回1个整型变量，成功返回0，失败返回-1，该函数有3个输入参数，如下

第1个输入参数为结构体指针ctrl，实际传递为全局变量ctrl_conn的值
第2个输入参数为待处理的参数个数argc，实际传递为argc - optind，即为4 - 3 = 1
第3个输入参数为具体的参数数组，实际为字符数组，内容为"scan"

该函数结构如下：

//wpa_supplicant\wpa_cli.c
struct wpa_cli_cmd {const char *cmd;int (*handler)(struct wpa_ctrl *ctrl, int argc, char *argv[]);char ** (*completion)(const char *str, int pos);enum wpa_cli_cmd_flags flags;const char *usage;
};//wpa_supplicant\wpa_cli.c
static const struct wpa_cli_cmd wpa_cli_commands[] = {{ "scan", wpa_cli_cmd_scan, NULL,cli_cmd_flag_none,"= request new BSS scan" },
}//wpa_supplicant\wpa_cli.c
static int wpa_request(struct wpa_ctrl *ctrl, int argc, char *argv[])
{const struct wpa_cli_cmd *cmd, *match = NULL;int count;int ret = 0;ifname_prefix = NULL;if (argc == 0)return -1;count = 0;cmd = wpa_cli_commands;while (cmd->cmd) {if (os_strncasecmp(cmd->cmd, argv[0], os_strlen(argv[0])) == 0){match = cmd;if (os_strcasecmp(cmd->cmd, argv[0]) == 0) {/* we have an exact match */count = 1;break;}count++;}cmd++;}if (count > 1) {printf("Ambiguous command '%s'; possible commands:", argv[0]);cmd = wpa_cli_commands;while (cmd->cmd) {if (os_strncasecmp(cmd->cmd, argv[0],os_strlen(argv[0])) == 0) {printf(" %s", cmd->cmd);}cmd++;}printf("\n");ret = 1;} else if (count == 0) {printf("Unknown command '%s'\n", argv[0]);ret = 1;} else {ret = match->handler(ctrl, argc - 1, &argv[1]);}return ret;
}

该函数将参数"scan"与已经定义的数组wpa_cli_commands中的命令元素进行完全匹配

while (cmd->cmd) {if (os_strncasecmp(cmd->cmd, argv[0], os_strlen(argv[0])) == 0){match = cmd;if (os_strcasecmp(cmd->cmd, argv[0]) == 0) {count = 1;break;}}cmd++;
}

匹配到相同的命令后调用该命令对应的句柄函数，并将未处理参数个数减1，scan后已经没有参数，所以此时传递给句柄的值为0

match->handler(ctrl, argc - 1, &argv[1]);

scan命令对应的句柄函数为wpa_cli_cmd_scan()，之后的调用关系如下：

继续调用到wpa_cli_cmd()函数，传递cmd参数为"SCAN"
继续调用到wpa_ctrl_command()函数，传递cmd参数为"SCAN"
继续调用到_wpa_ctrl_command()函数，传递cmd参数为"SCAN"
最终调用到wpa_ctrl_request()函数，传递cmd参数为"SCAN"，回调函数为wpa_cli_msg_cb()

主要函数调用如下：

//wpa_supplicant\wpa_cli.c
static int wpa_cli_cmd_scan(struct wpa_ctrl *ctrl, int argc, char *argv[])
{return wpa_cli_cmd(ctrl, "SCAN", 0, argc, argv);
}//wpa_supplicant\wpa_cli.c
static int wpa_cli_cmd(struct wpa_ctrl *ctrl, const char *cmd, int min_args,int argc, char *argv[])
{char buf[4096];if (write_cmd(buf, sizeof(buf), cmd, argc, argv) < 0)return -1;return wpa_ctrl_command(ctrl, buf);
}//wpa_supplicant\wpa_cli.c
static int wpa_ctrl_command(struct wpa_ctrl *ctrl, const char *cmd)
{return _wpa_ctrl_command(ctrl, cmd, 1);
}//wpa_supplicant\wpa_cli.c
static int _wpa_ctrl_command(struct wpa_ctrl *ctrl, const char *cmd, int print)
{char buf[4096];size_t len;int ret;len = sizeof(buf) - 1;ret = wpa_ctrl_request(ctrl, cmd, os_strlen(cmd), buf, &len,wpa_cli_msg_cb);return 0;
}

wpa_ctrl_request()函数返回1个整型变量，成功返回0，失败返回-1，该函数有6个输入参数，如下

参数ctrl是socket控制接口
参数cmd是发送给wpa_supplicant的命令
参数cmd_len是命令长度
参数reply是wpa_supplicant对命令的回复
参数reply_len是回复的长度
参数msg_cb是绑定的消息回调函数

该函数结构如下：

//src\common\wpa_ctrl.c
int wpa_ctrl_request(struct wpa_ctrl *ctrl,const char *cmd,size_t cmd_len,char *reply,size_t *reply_len,void (*msg_cb)(char *msg, size_t len))
{struct timeval tv;struct os_reltime started_at;int res;fd_set rfds;const char *_cmd;char *cmd_buf = NULL;size_t _cmd_len;{_cmd = cmd;_cmd_len = cmd_len;}errno = 0;started_at.sec = 0;started_at.usec = 0;
retry_send:if (send(ctrl->s, _cmd, _cmd_len, 0) < 0) {if (errno == EAGAIN || errno == EBUSY || errno == EWOULDBLOCK){if (started_at.sec == 0)os_get_reltime(&started_at);else {struct os_reltime n;os_get_reltime(&n);if (os_reltime_expired(&n, &started_at, 5))goto send_err;}os_sleep(1, 0);goto retry_send;}send_err:os_free(cmd_buf);return -1;}os_free(cmd_buf);for (;;) {tv.tv_sec = 10;tv.tv_usec = 0;FD_ZERO(&rfds);FD_SET(ctrl->s, &rfds);res = select(ctrl->s + 1, &rfds, NULL, NULL, &tv);if (res < 0 && errno == EINTR)continue;if (res < 0)return res;if (FD_ISSET(ctrl->s, &rfds)) {res = recv(ctrl->s, reply, *reply_len, 0);if (res < 0)return res;if ((res > 0 && reply[0] == '<') ||(res > 6 && strncmp(reply, "IFNAME=", 7) == 0)) {if (msg_cb) {if ((size_t) res == *reply_len)res = (*reply_len) - 1;reply[res] = '\0';msg_cb(reply, res);}continue;}*reply_len = res;break;} else {return -2;}}return 0;
}

该函数调用send()发送命令到wpa_supplicant

然后在for循环里调用select()监视使用的socket文件，添加到可读文件集合，超时时间设置为10s

然后调用recv()接收来自wpa_supplicant的回复

最后，如果回调函数存在，则调用回调函数msg_cb，因回调函数设置为wpa_cli_msg_cb，所以实际调用了wpa_cli_msg_cb()函数

//src\common\wpa_ctrl.c
static void wpa_cli_msg_cb(char *msg, size_t len)
{printf("%s\n", msg);
}

调用wpa_cli_msg_cb()函数时传递的mes参数为reply，所以该函数的功能是打印wpa_supplicant回复的消息

在终端显示的对命令sudo ./wpa_cli -i wlan0 scan的回复为ok

最后整个程序结束

1.4 wpa_supplicant的main函数

wpa_supplicant程序的入口为wpa_supplicant\main.c下的main()函数

//wpa_supplicant\main.c
int main(int argc, char *argv[])
{int c, i;struct wpa_interface *ifaces, *iface;int iface_count, exitcode = -1;struct wpa_params params;struct wpa_global *global;os_memset(&params, 0, sizeof(params));params.wpa_debug_level = MSG_INFO;iface = ifaces = os_zalloc(sizeof(struct wpa_interface));iface_count = 1;for (;;) {c = getopt(argc, argv,"b:Bc:C:D:de:f:g:G:hi:I:KLMm:No:O:p:P:qsTtuvW");if (c < 0)break;switch (c) {case 'c':iface->confname = optarg;break;case 'D':iface->driver = optarg;break;case 'i':iface->ifname = optarg;break;}}exitcode = 0;global = wpa_supplicant_init(&params);wpa_printf(MSG_INFO, "Successfully initialized " "wpa_supplicant");for (i = 0; exitcode == 0 && i < iface_count; i++) {struct wpa_supplicant *wpa_s;wpa_s = wpa_supplicant_add_iface(global, &ifaces[i], NULL);}if (exitcode == 0)exitcode = wpa_supplicant_run(global);return exitcode;
}

在main()函数中关于调试级别的设置语句为：

params.wpa_debug_level = MSG_INFO;

将调试级别设置为MSG_DEBUG，可以增加调试信息，修改如下

params.wpa_debug_level = MSG_DEBUG;

在main()函数中主要调用了以下函数

1）wpa_supplicant_init
2）wpa_supplicant_add_iface
3）wpa_supplicant_run

1.4.1 wpa_supplicant_add_iface函数

对关键的wpa_supplicant_add_iface()函数分析如下：

//wpa_supplicant\wpa_supplicant.c
struct wpa_supplicant * wpa_supplicant_add_iface(struct wpa_global *global,struct wpa_interface *iface,struct wpa_supplicant *parent)
{struct wpa_supplicant *wpa_s;struct wpa_interface t_iface;struct wpa_ssid *ssid;wpa_s = wpa_supplicant_alloc(parent);wpa_s->global = global;if (wpa_supplicant_init_iface(wpa_s, &t_iface)) {wpa_printf(MSG_DEBUG, "Failed to add interface %s",iface->ifname);wpa_supplicant_deinit_iface(wpa_s, 0, 0);return NULL;}wpa_s->next = global->ifaces;global->ifaces = wpa_s;return wpa_s;
}//wpa_supplicant\wpa_supplicant.c
static int wpa_supplicant_init_iface(struct wpa_supplicant *wpa_s,const struct wpa_interface *iface)
{wpa_printf(MSG_DEBUG, "Initializing interface '%s' conf '%s' driver ""'%s' ctrl_interface '%s' bridge '%s'", iface->ifname,iface->confname ? iface->confname : "N/A",iface->driver ? iface->driver : "default",iface->ctrl_interface ? iface->ctrl_interface : "N/A",iface->bridge_ifname ? iface->bridge_ifname : "N/A");wpa_s->ctrl_iface = wpa_supplicant_ctrl_iface_init(wpa_s);return 0;
}

接着会跳转到unix的控制接口文件中

//wpa_supplicant\ctrl_iface_unix.c
struct ctrl_iface_priv *wpa_supplicant_ctrl_iface_init(struct wpa_supplicant *wpa_s)
{struct ctrl_iface_priv *priv;priv = os_zalloc(sizeof(*priv));if (priv == NULL)return NULL;dl_list_init(&priv->ctrl_dst);dl_list_init(&priv->msg_queue);priv->wpa_s = wpa_s;priv->sock = -1;if (wpas_ctrl_iface_open_sock(wpa_s, priv) < 0) {os_free(priv);return NULL;}return priv;
}static int wpas_ctrl_iface_open_sock(struct wpa_supplicant *wpa_s,struct ctrl_iface_priv *priv)
{eloop_register_read_sock(priv->sock, wpa_supplicant_ctrl_iface_receive, wpa_s, priv);wpa_msg_register_cb(wpa_supplicant_ctrl_iface_msg_cb);
}

所以当wpa_supplicant程序接收到socket消息时就执行wpa_supplicant_ctrl_iface_receive()函数

//wpa_supplicant\ctrl_iface_unix.c
static void wpa_supplicant_ctrl_iface_receive(int sock,void *eloop_ctx,void *sock_ctx)
{struct wpa_supplicant *wpa_s = eloop_ctx;struct ctrl_iface_priv *priv = sock_ctx;char *buf;int res;struct sockaddr_storage from;socklen_t fromlen = sizeof(from);char *reply = NULL, *reply_buf = NULL;size_t reply_len = 0;int new_attached = 0;buf = os_malloc(CTRL_IFACE_MAX_LEN + 1);res = recvfrom(sock, buf, CTRL_IFACE_MAX_LEN + 1, 0,(struct sockaddr *) &from, &fromlen);buf[res] = '\0';reply_buf = wpa_supplicant_ctrl_iface_process(wpa_s, buf, &reply_len);reply = reply_buf;os_memset(buf, 0, res);if (!reply && reply_len == 1) {reply = "FAIL\n";reply_len = 5;} else if (!reply && reply_len == 2) {reply = "OK\n";reply_len = 3;}if (reply) {wpas_ctrl_sock_debug("ctrl_sock-sendto", sock, reply, reply_len);if (sendto(sock, reply, reply_len, 0, (struct sockaddr *) &from, fromlen) < 0) {int _errno = errno;wpa_dbg(wpa_s, MSG_DEBUG,"ctrl_iface sendto failed: %d - %s",_errno, strerror(_errno));}}os_free(reply_buf);os_free(buf);
}

在该函数主要中进行以下处理

调用recvfrom()函数接收来自wpa_cli的命令，将接收数据保存在字符指针buf里
调用wpa_supplicant_ctrl_iface_process()函数处理命令，返回结果保存在字符指针reply_buf和字符指针reply中
调用sendto()函数向socket发送回复reply

进一步分析wpa_supplicant接收wpa_cli的消息入口为wpa_supplicant_ctrl_iface_process()函数

//wpa_supplicant\ctrl_iface.c
char * wpa_supplicant_ctrl_iface_process(struct wpa_supplicant *wpa_s,char *buf,size_t *resp_len)
{char *reply;const int reply_size = 4096;int reply_len;int level = wpas_ctrl_cmd_debug_level(buf);wpa_dbg(wpa_s, level, "Control interface command '%s'", buf);reply = os_malloc(reply_size);os_memcpy(reply, "OK\n", 3);reply_len = 3;if (os_strcmp(buf, "SCAN") == 0) {wpas_ctrl_scan(wpa_s, NULL, reply, reply_size, &reply_len);} else if (os_strncmp(buf, "SCAN ", 5) == 0) {wpas_ctrl_scan(wpa_s, buf + 5, reply, reply_size, &reply_len);}if (reply_len < 0) {os_memcpy(reply, "FAIL\n", 5);reply_len = 5;}*resp_len = reply_len;return reply;
}//wpa_supplicant\ctrl_iface.c
static void wpas_ctrl_scan(struct wpa_supplicant *wpa_s, char *params,char *reply, int reply_size, int *reply_len)
{if (!wpa_s->sched_scanning && !wpa_s->scanning &&((wpa_s->wpa_state <= WPA_SCANNING) ||(wpa_s->wpa_state == WPA_COMPLETED))) {wpa_supplicant_req_scan(wpa_s, 0, 0);} else if (wpa_s->sched_scanning) {wpa_supplicant_req_scan(wpa_s, 0, 0);}
}

最终执行到scan.c文件中的wpa_supplicant_req_scan()函数，发起扫描请求

//wpa_supplicant\scan.c
void wpa_supplicant_req_scan(struct wpa_supplicant *wpa_s, int sec, int usec)
{int res;res = eloop_deplete_timeout(sec, usec, wpa_supplicant_scan, wpa_s,NULL);wpa_dbg(wpa_s, MSG_DEBUG, "Setting scan request: %d.%06d sec", sec, usec);eloop_register_timeout(sec, usec, wpa_supplicant_scan, wpa_s, NULL);
}

nl80211向底层驱动发送触发扫描的NL80211_CMD_TRIGGER_SCAN命令

wpa_driver_nl80211_scan()函数最后调用send_and_recv_msgs()函数

在该函数内继续调用send_and_recv()函数，在该函数内继续调用libnl库的nl_send_auto_complete()函数、nl_recvmsgs()函数向内核驱动发送和接收消息

其中，libnl（Linux Netlink库）是一个用于处理Linux内核通信机制Netlink的C库

调用到nl80211驱动，接收到底层驱动返回给nl80211驱动接口的NL80211_CMD_TRIGGER_SCAN触发扫描驱动事件

nl80211驱动上报给wpa_supplicant的event事件