1，引入

????????ubus提供了一種多進程通信的機制。存在一個守護進程ubusd，所以進程都注冊到ubusd，ubusd進行消息的接收、分發管理。

ubus對多線程支持的不好，例如在多個線程中去請求同一個服務，就有可能出現不可預知的結果。

ubus通信一共有三種實現方式：①端對端通信? ②訂閱/通知? ③事件（廣播）

2，ubus命令的使用

ubus list ：列出所有對象   
ubus -v list network.interface.lan : 查看指定對象的詳細信息

ubus call network.interface.lan status ：執行指定對象的方法并獲取返回結果

ubus listen [事件類型]: 實時接收指定或所有 ubus 事件 

ubus send test.event '{"message":"Hello World"}'  ： 發送自定義事件

? ubus subscribe mytest : 訂閱mytest事件

3，向UBUS注冊一個對象

主要步驟：uloop_init(); ubus_connect(NULL);ubus_add_uloop(ser_ctx);初始化object，ubus_add_object(ser_ctx, &sub_object);

代碼實現：

int get_no_arg_info(struct ubus_context *ctx, struct ubus_object *obj,struct ubus_request_data *req, const char *method,struct blob_attr *msg)
{struct blob_buf b = {};blob_buf_init(&b, 0);blobmsg_add_string(&b, "obj_name", obj->name);blobmsg_add_u32(&b, "pid", (uint32_t)getpid());blobmsg_add_u32(&b, "uptime", (uint32_t)time(NULL));ubus_send_reply(ctx, req, b.head);blob_buf_free(&b);return 0;
}enum parm_num {T_ID = 0,T_NAME,T_AGE,T_MAX
};static const struct blobmsg_policy t_policy[] = {[T_ID]   = { .name = "id", .type = BLOBMSG_TYPE_INT32 },[T_NAME] = { .name = "name", .type = BLOBMSG_TYPE_STRING },[T_AGE]  = { .name = "age", .type = BLOBMSG_TYPE_INT32 },
};int get_arg_info(struct ubus_context *ctx, struct ubus_object *obj,struct ubus_request_data *req, const char *method,struct blob_attr *msg)
{int i = 0;struct blob_attr *tb[T_MAX];blobmsg_parse(t_policy, ARRAY_SIZE(t_policy), tb, blob_data(msg), blob_len(msg));for(i = 0; i < T_MAX; i++){if(!tb[i]){fprintf(stderr, "Failed to parse arg '%d'.\n", i);return -1;}}printf("-->id:   %d\n", blobmsg_get_u32(tb[T_ID]));printf("-->name: %s\n", blobmsg_get_string(tb[T_NAME]));printf("-->age:  %d\n", blobmsg_get_u32(tb[T_AGE]));return 0;
}static const struct ubus_method test_obj_methods[] = {UBUS_METHOD_NOARG("get_no_arg_info", get_no_arg_info),UBUS_METHOD( "get_arg_info", get_arg_info, t_policy),
};static struct ubus_object_type test_obj_type = UBUS_OBJECT_TYPE("test.service", test_obj_methods);static struct ubus_object test_object = {.name = "test.service",.type = &test_obj_type,.methods = test_obj_methods,.n_methods = ARRAY_SIZE(test_obj_methods),
};int main()
{int ret = 0;struct ubus_context *mytest_ctx = NULL;uloop_init();mytest_ctx = ubus_connect(NULL);if(!mytest_ctx) {fprintf(stderr, "Failed to connect ubus.\n");return ERROR;}ret = ubus_add_object(mytest_ctx, &test_object);if(ret) {fprintf(stderr, "Failed to add 'mytest' obj.\n");return ERROR;}ubus_add_uloop(mytest_ctx);uloop_run();ubus_free(mytest_ctx);uloop_done();
}

測試：

補充：實現了ubus call 去獲取test.service

void mytest_reply_cb(struct ubus_request *req, int type, struct blob_attr *msg)
{struct blob_buf buf = {};char *str;if (!msg) {printf("No response received\n");return;}str = blobmsg_format_json(msg, true);if (str) {printf("\nReceived response:\n%s\n", str);free(str);}
}int main()
{int ret = 0;int i = 0;int mydemo_id = 0;struct ubus_context *myclient_ctx = NULL;struct ubus_request req;uloop_init();myclient_ctx =  ubus_connect(NULL);if(!myclient_ctx) {fprintf(stderr, "Failed to connect ubus.\n");return ERROR;}ret = ubus_lookup_id(myclient_ctx, "test.service", &mydemo_id);if (ret) {fprintf(stderr, "Failed to lookup test object: %s\n", ubus_strerror(ret));return ERROR;}ubus_add_uloop(myclient_ctx);#if 0 //不帶參數請求test.service ->get_no_arg_info方法ret = ubus_invoke(myclient_ctx, mydemo_id, "get_no_arg_info", NULL, mytest_reply_cb, &req, 1000);if (ret) {fprintf(stderr, "Failed to call get_no_arg_info: %s\n", ubus_strerror(ret));return ret;}//ubus_complete_request(myclient_ctx, &req, 1000);#else //帶參數請求test.service ->get_no_arg_info方法struct blob_buf msg = {};blob_buf_init(&msg, 0);blobmsg_add_string(&msg, "name", "Hello");blobmsg_add_u32(&msg, "id", 12);blobmsg_add_u32(&msg, "age", 36);memset( &req, 0, sizeof(req));ret = ubus_invoke(myclient_ctx, mydemo_id, "get_arg_info", msg.head, mytest_reply_cb, &req, 1000);if (ret) {fprintf(stderr, "Failed to call get_no_arg_info: %s\n", ubus_strerror(ret));return ret;}//ubus_complete_request(myclient_ctx, &req, 1000);blob_buf_free(&msg);#endifuloop_run();ubus_free(myclient_ctx);uloop_done();}

?結果：

該打印由get_arg_info打印，我發送過去的msg。

總結：

??????? 1，實現了向UBUS添加一個object的代碼，需要依賴Ubus頭文件：#include <libubox/blobmsg_json.h>? #include <libubus.h>

??????? 2，比較繁瑣的點是在test_object這個結構體的初始化，無參數調用使用UBUS_METHOD_NOARG， 有參數調用使用：UBUS_METHOD,此時UBUS_METHOD的后兩個參數不能填NULL,否則段錯誤。

??????? 3，使用UBUS 命令call，其內部ubus_invoke，實現UBUS端到端通信。