帮我解读并注释这段代码static int wan_config_get(struct ubus_context *ctx, struct ubus_object *obj, struct ubus_request_data *req, const char *method, struct blob_attr *msg) { T_CTCAPD_WANINFO ctcapd_waninfo_get; INT32 iRet = RET_PM_OK; struct blob_buf *buf = &g_buf; char wan_default_mac[24] = {'\0'}; #ifdef SAFEKEY_H_ char encry_pwd[512+1] = {'\0'}; #endif memset(&ctcapd_waninfo_get, 0x00, sizeof(T_CTCAPD_WANINFO)); iRet = pm_ubus_waninfo_get(&ctcapd_waninfo_get); if (iRet != RET_PM_OK) { OssUserLogError("pm_ubus_dns_config_get fail"); return UBUS_STATUS_UNKNOWN_ERROR; } if(pm_ubus_get_wan_default_mac(NULL, wan_default_mac)) return UBUS_STATUS_UNKNOWN_ERROR; blob_buf_init(buf, 0); ToLowerStr(ctcapd_waninfo_get.networktype); blobmsg_add_string(buf, "proto", ctcapd_waninfo_get.networktype); blobmsg_add_string(buf, "defaultmac", wan_default_mac); if(strcmp(ctcapd_waninfo_get.dhcp_macaddr, "00:00:00:00:00:00")) blobmsg_add_string(buf, "macaddr", ctcapd_waninfo_get.dhcp_macaddr); else blobmsg_add_string(buf, "macaddr", wan_default_mac); blobmsg_add_u32(buf, "mtu", ctcapd_waninfo_get.mtu); blobmsg_add_string(buf, "mode", "nat"); blobmsg_add_string(buf, "username", ctcapd_waninfo_get.pppoename);

这段代码是一个函数，函数名为`wan_config_get`，接受一些参数，并返回一个整型值。下面是对代码的解读和注释：

static int wan_config_get(struct ubus_context *ctx, struct ubus_object *obj,
                          struct ubus_request_data *req, const char *method,
                          struct blob_attr *msg)
{
    // 声明和初始化变量
    T_CTCAPD_WANINFO ctcapd_waninfo_get;
    INT32 iRet = RET_PM_OK;
    struct blob_buf *buf = &g_buf;
    char wan_default_mac[24] = {'\0'};
#ifdef SAFEKEY_H_
    char encry_pwd[512+1] = {'\0'};
#endif

    // 清空ctcapd_waninfo_get结构体
    memset(&ctcapd_waninfo_get, 0x00, sizeof(T_CTCAPD_WANINFO));
    
    // 调用pm_ubus_waninfo_get函数，获取WAN信息
    iRet = pm_ubus_waninfo_get(&ctcapd_waninfo_get);
    if (iRet != RET_PM_OK)
    {
        OssUserLogError("pm_ubus_dns_config_get fail");
        return UBUS_STATUS_UNKNOWN_ERROR;
    }

    // 调用pm_ubus_get_wan_default_mac函数，获取默认的MAC地址
    if(pm_ubus_get_wan_default_mac(NULL, wan_default_mac))
        return UBUS_STATUS_UNKNOWN_ERROR;

    // 初始化blob_buf
    blob_buf_init(buf, 0);
    
    // 将网络类型添加到buf中
    ToLowerStr(ctcapd_waninfo_get.networktype);
    blobmsg_add_string(buf, "proto", ctcapd_waninfo_get.networktype);
    
    // 将默认的MAC地址添加到buf中
    blobmsg_add_string(buf, "defaultmac", wan_default_mac);
    
    // 如果dhcp_macaddr不等于"00:00:00:00:00:00"，则将其添加到buf中
    if(strcmp(ctcapd_waninfo_get.dhcp_macaddr, "00:00:00:00:00:00"))
        blobmsg_add_string(buf, "macaddr", ctcapd_waninfo_get.dhcp_macaddr);
    else
        blobmsg_add_string(buf, "macaddr", wan_default_mac);
    
    // 将mtu添加到buf中
    blobmsg_add_u32(buf, "mtu", ctcapd_waninfo_get.mtu);
    
    // 将mode添加到buf中
    blobmsg_add_string(buf, "mode", "nat");
    
    // 将pppoename添加到buf中
    blobmsg_add_string(buf, "username", ctcapd_waninfo_get.pppoename);
    
    // ...
}

这段代码主要是从`pm_ubus_waninfo_get`函数中获取WAN信息，并将获取到的信息添加到一个`blob_buf`中。其中，`pm_ubus_waninfo_get`函数用于获取WAN信息，`pm_ubus_get_wan_default_mac`函数用于获取默认的MAC地址。最后，将获取到的信息添加到`buf`中，包括网络类型、默认MAC地址、DHCP MAC地址、MTU、模式和用户名等。