ubus 介绍

转载https://www.cnblogs.com/gr-nick/p/10805608.html

一、 介绍

ubus提供了一种多进程通信的机制。存在一个守护进程ubusd,所以进程都注册到ubusd,ubusd进行消息的接收、分发管理。

  1. ubus依赖于ubox
  2. ubus启动后会在后台运行ubusd进程,该进程监听一个unix套接字用于与其他应用程序通信。其他应用程序可基于libubox提供的接口(或自己实现)与其通信。
  3. ubus是为发送消息而设计的,不合适传输大量数据。

 

ubus 介绍_第1张图片

ubusd

 

二、三种实现方式:

1. invoke的方式实现端对端通信

server端:ubus_send_reply(ctx, req, b.head);

uloop_init(); 
ctx = ubus_connect(NULL);
ubus_add_uloop(ctx);
static struct ubus_method scan_methods[] =   
{  
    UBUS_METHOD("scan", ubus_start_scan, scan_policy),  
};  
static struct ubus_object scan_obj =   
{  
    .name = "scan_prog", /* 对象的名字 */  
    .type = &scan_obj_type,  
    .methods = scan_methods,  
    .n_methods = ARRAY_SIZE(scan_methods),  
};  
ubus_add_object(ctx, scan_obj);
ubus_send_reply(ctx, req, b.head); 
uloop_run();
ubus_free(ctx);

client端:ubus_invoke(ctx, id, "scan", b.head, scanreq_prog_cb, NULL, timeout * 1000);

uloop_init(); 
ctx = ubus_connect(path);
struct blob_buf b;
blob_buf_init(&b, 0);
ubus_lookup_id(ctx, "scan_prog", &id); 
ubus_invoke(ctx, id, "scan", b.head, scanreq_prog_cb, NULL, timeout * 1000); 
ubus_free(ctx);

2. subscribe/notify的方式实现订阅

server端:ubus_notify(ctx, &test_object, "say Hi!", NULL, -1);


static struct ubus_object test_object = {  
    .name = "test", /* object的名字 */  
    .type = &test_obj_type,  
    .subscribe_cb = test_client_subscribe_cb,  
}; 

static void test_client_subscribe_cb(struct ubus_context *ctx, struct ubus_object *obj)  
{  
    fprintf(stderr, "Subscribers active: %d\n", obj->has_subscribers);  
} 

uloop_init();
ctx = ubus_connect(NULL);  
ubus_add_uloop(ctx);  
ret = ubus_add_object(ctx, &test_object); 
while (1) {  
    sleep(2);  
    /* step2: 广播notification消息。 */  
    ubus_notify(ctx,  &test_object, "say Hi!", NULL, -1);  
}  
uloop_run();  
ubus_free(ctx);  
uloop_done();  

client端:ret = ubus_register_subscriber(ctx, &test_event);

static int test_notify(struct ubus_context *ctx, struct ubus_object *obj, struct ubus_request_data *req,   const char *method, struct blob_attr *msg)  
{  
    printf("notify handler...\n");  
}

static void test_handle_remove(struct ubus_context *ctx,  
                      struct ubus_subscriber *obj, uint32_t id)  
{  
    printf("remove handler...\n");  
}


uloop_init(); 
ctx = ubus_connect(NULL); 
ubus_add_uloop(ctx);
struct ubus_subscriber test_event;
/* 通知到来时的处理函数。 */  
test_event.cb = test_notify;  
test_event.remove_cb = test_handle_remove; //server主动发起删除该client的订阅的cb函数(如server退出的时候)  
/* 注册test_event */  
ret = ubus_register_subscriber(ctx, &test_event); 
uint32_t obj_id;
ret = ubus_lookup_id(ctx, "test", &obj_id); 
ret = ubus_subscribe(ctx, &test_event, obj_id); 

uloop_run();  
ubus_free(ctx);  
uloop_done(); 

3. 广播事件

server端:发送事件广播消息, ubus_send_event(ctx, "add_device", b.head);

uloop_init(); 
ctx = ubus_connect(NULL);
blob_buf_init(&b, 0);  
/* 需要传递的参数 */  
blobmsg_add_u32(&b, "major", 3);  
blobmsg_add_u32(&b, "minor", 56);  
blobmsg_add_string(&b, "name", "mmc01");  
/* 广播名为"add_device"的事件 */  
return ubus_send_event(ctx, "add_device", b.head); 
ubus_free(ctx);

client端:ret = ubus_register_event_handler(ctx, &listener, "add_device");

    #define UBUS_EVENT_ADD_DEVICE   "add_device"  
    #define UBUS_EVENT_REMOVE_DEVICE    "rm_device"  
    static void ubus_probe_device_event(struct ubus_context *ctx, struct ubus_event_handler *ev,  
              const char *type, struct blob_attr *msg)  
    {  
        char *str;  

        if (!msg)  
            return;  

        str = blobmsg_format_json(msg, true);  
        printf("{ \"%s\": %s }\n", type, str);  
        free(str);  
    }  

    uloop_init();        
    ctx = ubus_connect(NULL); 
    ubus_add_fd();	
    ubus_add_uloop(ctx);
    
    static struct ubus_event_handler listener;   
    memset(&listener, 0, sizeof(listener));  
    listener.cb = ubus_probe_device_event;  
    ret = ubus_register_event_handler(ctx, &listener, UBUS_EVENT_ADD_DEVICE);
    ret = ubus_register_event_handler(ctx, &listener, UBUS_EVENT_REMOVE_DEVICE);
    
    uloop_run(); 
    ubus_free(ctx);
    

三、uloop源码

1. uloop_init

/**
 *初始化事件循环
 *主要工作是poll_fd = epoll_create(32);/* 创建一个epoll的文件描述符监控句柄。最多监控32个文件描述符 
 **/
int uloop_init(void)
{
    if (poll_fd >= 0)
        return 0;
 
    poll_fd = epoll_create(32);/* 创建一个epoll的句柄。最多监控32个文件描述符 */
    if (poll_fd < 0)
        return -1;
 
    fcntl(poll_fd, F_SETFD, fcntl(poll_fd, F_GETFD) | FD_CLOEXEC); /* fd_cloexecs */
    return 0;
}

2. uloop_run

/**
 * 事件循环主处理入口
 *1.当某一个进程第一次调用uloop_run时,注册sigchld和sigint信号
 *2.循环获取当前时间,把超时的timeout处理掉,有一条timeout链表在维护
 *3.循环检测是否收到一个sigchld信号,如果收到,删除对应的子进程,有一条process子进程链表在维护
 *4.循环调用epoll_wait 监相应的触发事件文件描述符fd 
 **/
void uloop_run(void)
{
    static int recursive_calls = 0; /* static value */
    struct timeval tv;
 
    /*
     * Handlers are only updated for the first call to uloop_run() (and restored
     * when this call is done).
     */
    if (!recursive_calls++) /* 第一次运行uloop_run时调用, 注册信号处理函数 */
        uloop_setup_signals(true);
 
    uloop_cancelled = false;
    while(!uloop_cancelled)
    {
        uloop_gettime(&tv); /* 获取当前时间 */
        uloop_process_timeouts(&tv); /* 把超时的timeout清理掉 */
        if (uloop_cancelled)
            break;
 
        if (do_sigchld) /*  收到一个sigchld的信号 */
            uloop_handle_processes(); /* 销毁该进程的uloop_process */
        uloop_gettime(&tv);
        uloop_run_events(uloop_get_next_timeout(&tv));/* 处理相应的触发事件fd */
    }
 
    if (!--recursive_calls)
        uloop_setup_signals(false);
}

3. uloop_done

/**
 * 销毁事件循环
 * 关闭epoll描述符
 * 销毁子进程链表
 * 销毁timeout链表
**/
void uloop_done(void)
{
    if (poll_fd < 0)
        return;
 
    close(poll_fd);
    poll_fd = -1;
 
    uloop_clear_timeouts();
    uloop_clear_processes();
}

四、uloop三种使用

1. socket使用

uloop_fd_add(uloop_fd, ULOOP_READ);

#include ""  
  
struct uloop_fd ufd;    //创建uloop_fd全局变量  
  
static void fd_handler(struct uloop_fd *u, unsigned int ev)  
{  
    if(recvfrom(u->fd, ...)) == -1) {  
      
    } else {  
        //do your work  
    }  
}  
  
int main()  
{  
    //  
    int socket = socket(....);  
      
    ufd.fd = socket;  
      
    uloop_init();           //使用库初始化      
      
    ufd.cb = fd_handler;  
  
    uloop_fd_add(&ufd, ULOOP_READ));  
  
    uloop_run();  
}  

2. 定时器使用

uloop_timeout_set(uloop_timeout, freq);

#include ""  
  
struct uloop_timeout timeout;   //创建uloop_timeout全局变量  
  
int frequency = 5; //每隔5秒超时一次  
  
static void timeout_cb(struct uloop_timeout *t)  
{  
    //do your work  
      
    uloop_timeout_set(t, frequency * 1000);//设置下次的超时时间  
}  
  
int main()  
{     
    uloop_init();           //使用库初始化      
      
    timeout.cb = timeout_cb;  
      
    uloop_timeout_set(&timeout, frequency * 1000);//设置下次的超时时间  
  
    uloop_run();  
}  

3. 子进程使用

uloop_process_add(uloop_process);

#include ""  
  
static struct uloop_process rsync;  //创建rsync全局变量  
  
static void rsync_complete(struct uloop_process *proc, int ret)  
{  
    //do something where child exit;  
    printf("rsync work is complete\n");  
}  
  
function fun()   
{  
    char *argv[]={"rsync", "-az", "rsync://[email protected]/www","/root/www/","--password-file=/root/rsync.secrets", NULL};  
    rsync.cb = rsync_complete;  
    rsync.pid = fork();  
  
    if (!rsync.pid) {  
        /* This is child process*/  
        execvp(argv[0], argv);  
        fprintf(stderr, "fork failed\n");  
        exit(-1);  
    }  
  
    if (rsync.pid <=0) {  
        fprintf(stderr, "fork failed2\n");  
        return -1;  
    }  
  
    uloop_process_add(&rsync);  
  
}  
  
  
int main()  
{  
      
    .....  
      
    uloop_init();   //使用库前进行初始化  
      
    fun();  
      
    uloop_run();  
      
}  

五、数据传输

1. blobmsg

 

ubus 介绍_第2张图片

enter description here

 

初始化:

json_uri = blobmsg_open_array(&b, "prog_list");  
for (idx = 0; idx < PROG_MAX; idx++)  
{  
    if ('\0' != uri_list[idx].name[0])  
    {  
        json_list = blobmsg_open_table(&b, NULL);  
        blobmsg_add_string(&b, "name", uri_list[idx].name);  
        blobmsg_add_u32(&b, "channel", uri_list[idx].chn_id);  
        blobmsg_close_table(&b, json_list);  
    }  
}  
blobmsg_close_array(&b, json_uri); 

解析:
获取索引: hdr = blob_data(attr); char *name = (char *)hdr->name;
获取数据: blobmsg_get_u32(attr);
获取长度: int len = blobmsg_data_len(tb[RSP_GET_STREAMINFO_ABILITY]);

struct blob_attr *tb[SCAN_POLICY_MAX];  
blobmsg_parse(scan_policy, SCAN_POLICY_MAX, tb, blob_data(msg), blob_len(msg));  
struct blob_attr *head = blobmsg_data(tb[RSP_GET_STREAMINFO_ABILITY]);
int len = blobmsg_data_len(tb[RSP_GET_STREAMINFO_ABILITY]);
struct blob_attr *attr;
struct blobmsg_hdr *hdr;

__blob_for_each_attr(attr, head, len) {
    hdr = blob_data(attr);
    struct blob_attr *head_temp;
    struct blob_attr *attr_temp;
    int len_temp;
    char *name = (char *)hdr->name;

    if (!strcmp(name, "fmt_number"))
        rsp->ability.fmt_number = blobmsg_get_u32(attr);
    else if (!strcmp(name, "frmival_num"))
        rsp->ability.frmival_num =	blobmsg_get_u32(attr);
}

六、Problem

现在使用中遇到了多线程的问题,由于ubus许多变量都是全局变量,对多线程的支持并不好。比如同时在两个线程中监听广播和发送消息,就会出现segment错误:
解决方法,最好能把两个操作放到一个线程中,比如在监听的回调函数中发送消息,不好的就是要根据发送消息的频率去设置回调函数的timeout。

Reference

https://blog.csdn.net/xiaoxiaozhu2010/article/details/78645339
https://www.cnblogs.com/embedded-linux/p/6791560.html

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