Android : 跟我学Binder --- (3) C程序示例

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目录：

• Android : 跟我学Binder --- (1) 什么是Binder IPC？为何要使用Binder机制？

• Android : 跟我学Binder --- (2) AIDL分析及手动实现

• Android : 跟我学Binder --- (3) C程序示例

• Android : 跟我学Binder --- (4) 驱动情景分析

• Android : 跟我学Binder --- (5) C++实现

• Android : 跟我学Binder --- (6)  JAVA实现

 

 

一、Binder框架分析

　　1、IPC、LPC和RPC的概念：

　　　　IPC:  （Inter Process Communication ）跨进程通信，泛指进程之间任何形式的通信行为，它不仅包括各种形式的消息传递，还可以指共享资源，以及同步对象；

　　　　LPC: （Local Procedure Call ）本地过程调用，用在多任务操作系统中，使得同时运行的任务能互相会话。这些任务共享内存空间使任务同步和互相发送信息；（IPC的封装）

　　　　RPC:（Reomote Procedure Call ）远程过程调用，类似于LPC，只是在网上工作。RPC开始是出现在Sun微系统公司和HP公司的运行UNIX操作系统的计算机中；

 

　　2、通信架构：

　　　　Client/Server <---> service manager 交互流程：

　　　　　　server ---------addservice-------> service manager

　　　　　　client  ---------getservice--------> service manager

 注：ServiceManager首先向binder驱动注册为服务管理者，handle为0；

 

　　3、简析示例代码(非完整流程)：

①android_5.0.2_32\frameworks\native\cmds\servicemanager\service_manager.c  //管理server注册的服务（进程）

　　　　a. binder_open  //打开驱动
　　　　b. binder_become_context_manager //告诉驱动注册为service manager
　　　　c. binder_loop(bs, svcmgr_handler);
   　　　　c.1 res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);  //读数据
   　　　　c.2 binder_parse // 解析数据
    
         　/*处理数据  : svcmgr_handler*/
                     SVC_MGR_GET_SERVICE/SVC_MGR_CHECK_SERVICE : 获取服务
                     SVC_MGR_ADD_SERVICE : 注册服务
        　 /*有必要则回复数据*/  
　　　　　　　　　　　　 ....... 

 

②android_5.0.2_32\frameworks\native\cmds\servicemanager\bctest.c  //client测试代码

　  注册服务的过程:
　　　　a. binder_open　　//打开驱动
　　　　b. svcmgr_publish  //构造数据　　　
　　　　c. binder_call(bs, &msg, &reply, 0, SVC_MGR_ADD_SERVICE)
                   　　　　// 含有服务的名字
                         　　　　// 它会含有servicemanager回复的数据
                                　　　  // 0表示servicemanager
                                    　　　　// code: 表示要调用servicemanager中的"addservice函数"

　　获取服务的过程:
　　　　a. binder_open //打开驱动
　　　　b. svcmgr_lookup //构造数据
　　　　c. binder_call(bs, &msg, &reply, 0, SVC_MGR_CHECK_SERVICE)
                  　　　　 // 含有服务的名字
                         　　　　// 它会含有servicemanager回复的数据, 表示提供服务的进程
                                　　　　// 0表示servicemanager
                                   　　　　 // code: 表示要调用servicemanager中的"getservice函数

 

③android_5.0.2_32\frameworks\native\cmds\servicemanager\binder.c  //封装好的C函数

（1）构造参数：放在一个buffer用binder_io来描述；

　　 unsigned iodata[512/4]; //用binder_io来管理这个缓冲区
    struct binder_io msg, reply;
...
    bio_init(&msg, iodata, sizeof(iodata), 4); //初始化binder_io对象

　　/*可以放入各类型参数，反之通过get方法获取*/
    bio_put_uint32(&msg, 0);  // strict mode header
    bio_put_string16_x(&msg, SVC_MGR_NAME); 
    bio_put_string16_x(&msg, name);
    bio_put_obj(&msg, ptr);
...

/*调用binder_call(struct binder_state *bs,
　　　　　　　　　　struct binder_io *msg/*提供参数*/, 
　　　　　　　　　　struct binder_io *reply/*获得回复*/,
　　　　　　　　　　uint32_t target/*发送对象*/,
　　　　　　　　　　uint32_t code/*调用函数*/)*/

    if (binder_call(bs, &msg, &reply, target, SVC_MGR_ADD_SERVICE))
        return -1;

 

（2）根据 binder_io、target、code 构造writebuf:

    struct binder_write_read bwr;
    struct {
        uint32_t cmd;
        struct binder_transaction_data txn;
    } __attribute__((packed)) writebuf;
    unsigned readbuf[32];
....

    writebuf.cmd = BC_TRANSACTION;
    writebuf.txn.target.handle = target;
    writebuf.txn.code = code;
    writebuf.txn.flags = 0;
    writebuf.txn.data_size = msg->data - msg->data0;
    writebuf.txn.offsets_size = ((char*) msg->offs) - ((char*) msg->offs0);
    writebuf.txn.data.ptr.buffer = (uintptr_t)msg->data0;
    writebuf.txn.data.ptr.offsets = (uintptr_t)msg->offs0;

    bwr.write_size = sizeof(writebuf);
    bwr.write_consumed = 0;
    bwr.write_buffer = (uintptr_t) &writebuf;

　　其中binder_write_read 结构体在内核代码中的定义：

struct binder_write_read {
    signed long    write_size;    /* bytes to write */
    signed long    write_consumed;    /* bytes consumed by driver */
    unsigned long    write_buffer;
    signed long    read_size;    /* bytes to read */
    signed long    read_consumed;    /* bytes consumed by driver */
    unsigned long    read_buffer;
};

　　其中binder_transaction_data结构体在内核代码中的定义：

struct binder_transaction_data {
    /* The first two are only used for bcTRANSACTION and brTRANSACTION,
     * identifying the target and contents of the transaction.
     */
    union {
        size_t    handle;    /* target descriptor of command transaction */
        void    *ptr;    /* target descriptor of return transaction */
    } target;
    void        *cookie;    /* target object cookie */
    unsigned int    code;        /* transaction command */

    /* General information about the transaction. */
    unsigned int    flags;
    pid_t        sender_pid;
    uid_t        sender_euid;
    size_t        data_size;    /* number of bytes of data */
    size_t        offsets_size;    /* number of bytes of offsets */

    /* If this transaction is inline, the data immediately
     * follows here; otherwise, it ends with a pointer to
     * the data buffer.
     */
    union {
        struct {
            /* transaction data */
            const void    *buffer;
            /* offsets from buffer to flat_binder_object structs */
            const void    *offsets;
        } ptr;
        uint8_t    buf[8];
    } data;
};

 

（3）通过ioctl发送数据：

    for (;;) {
        bwr.read_size = sizeof(readbuf);
        bwr.read_consumed = 0;
        bwr.read_buffer = (uintptr_t) readbuf;

        res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);

        if (res < 0) {
            fprintf(stderr,"binder: ioctl failed (%s)\n", strerror(errno));
            goto fail;
        }

        res = binder_parse(bs, reply, (uintptr_t) readbuf, bwr.read_consumed, 0); //解析返回的数据
        if (res == 0) return 0;
        if (res < 0) goto fail;
    }

 

框架流程总结：

 　client端： binder_open ---> 获得服务handle ---> 构造参数binder_io ---> 调用binder_call ---> 解析返回的binder_io；

　 server端：binder_open ---> 注册服务 ---> ioctl读取数据（binder_write_read ）---> 解析数据（binder_transaction_data ） ---> 获得binder_io并根据code调用对应函数 ---> 把返回值发送给client；

 

 

二、编写程序

　　1.参考service_manager.c编写test_server.c添加服务：

/* Copyright 2008 The Android Open Source Project
 */

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <linux/types.h>
#include<stdbool.h>
#include <string.h>

#include <private/android_filesystem_config.h>

#include "binder.h"
#include "test_server.h"

int svcmgr_publish(struct binder_state *bs, uint32_t target, const char *name, void *ptr)
{
    int status;
    unsigned iodata[512/4];
    struct binder_io msg, reply;

    bio_init(&msg, iodata, sizeof(iodata), 4);
    bio_put_uint32(&msg, 0);  // strict mode header
    bio_put_string16_x(&msg, SVC_MGR_NAME);
    bio_put_string16_x(&msg, name);
    bio_put_obj(&msg, ptr);

    if (binder_call(bs, &msg, &reply, target, SVC_MGR_ADD_SERVICE))
        return -1;

    status = bio_get_uint32(&reply);

    binder_done(bs, &msg, &reply);

    return status;
}

void sayhello(void)
{
    static int cnt = 0;
    fprintf(stderr, "say hello : %d\n", ++cnt);
}


int sayhello_to(char *name)
{
    static int cnt = 0;
    fprintf(stderr, "say hello to %s : %d\n", name, ++cnt);
    return cnt;
}

void saygoodbye(void)
{
    static int cnt = 0;
    fprintf(stderr, "say goodbye : %d\n", ++cnt);
}


int saygoodbye_to(char *name)
{
    static int cnt = 0;
    fprintf(stderr, "say goodbye to %s : %d\n", name, ++cnt);
    return cnt;
}


int hello_service_handler(struct binder_state *bs,
                   struct binder_transaction_data *txn,
                   struct binder_io *msg,
                   struct binder_io *reply)
{
    /* 根据txn->code知道要调用哪一个函数
     * 如果需要参数, 可以从msg取出
     * 如果要返回结果, 可以把结果放入reply
     */

    /* sayhello
     * sayhello_to
     */
    
    uint16_t *s;
    char name[512];
    size_t len;
    uint32_t handle;
    uint32_t strict_policy;
    int i;


    // Equivalent to Parcel::enforceInterface(), reading the RPC
    // header with the strict mode policy mask and the interface name.
    // Note that we ignore the strict_policy and don't propagate it
    // further (since we do no outbound RPCs anyway).
    strict_policy = bio_get_uint32(msg); // 取出0，后面才是传过来的所需数据


    switch(txn->code) {
    case HELLO_SVR_CMD_SAYHELLO:
        sayhello();
        bio_put_uint32(reply, 0); /* no exception */
        return 0;

    case HELLO_SVR_CMD_SAYHELLO_TO:
        /* 从msg里取出字符串（16位转8位） */
        s = bio_get_string16(msg, &len);  //"IHelloService"
        s = bio_get_string16(msg, &len);  // name
        if (s == NULL) {
            return -1;
        }
        for (i = 0; i < len; i++)
            name[i] = s[i];
        name[i] = '\0';

        /* 处理 */
        i = sayhello_to(name);

        /* 把结果放入reply */
        bio_put_uint32(reply, 0); /* no exception */
        bio_put_uint32(reply, i);
        
        break;

    default:
        fprintf(stderr, "unknown code %d\n", txn->code);
        return -1;
    }

    return 0;
}



int goodbye_service_handler(struct binder_state *bs,
                   struct binder_transaction_data *txn,
                   struct binder_io *msg,
                   struct binder_io *reply)
{
    /* 根据txn->code知道要调用哪一个函数
     * 如果需要参数, 可以从msg取出
     * 如果要返回结果, 可以把结果放入reply
     */

    /* sayhello
     * sayhello_to
     */
    
    uint16_t *s;
    char name[512];
    size_t len;
    uint32_t handle;
    uint32_t strict_policy;
    int i;


    // Equivalent to Parcel::enforceInterface(), reading the RPC
    // header with the strict mode policy mask and the interface name.
    // Note that we ignore the strict_policy and don't propagate it
    // further (since we do no outbound RPCs anyway).
    strict_policy = bio_get_uint32(msg);


    switch(txn->code) {
    case GOODBYE_SVR_CMD_SAYGOODBYE:
        saygoodbye();
        bio_put_uint32(reply, 0); /* no exception */
        return 0;

    case GOODBYE_SVR_CMD_SAYGOODBYE_TO:
        /* 从msg里取出字符串（16位转8位） */
        s = bio_get_string16(msg, &len);  //"IGoodbyeService"
        s = bio_get_string16(msg, &len);  // name
        if (s == NULL) {
            return -1;
        }
        for (i = 0; i < len; i++)
            name[i] = s[i];
        name[i] = '\0';

        /* 处理 */
        i = saygoodbye_to(name);

        /* 把结果放入reply */
        bio_put_uint32(reply, 0); /* no exception */
        bio_put_uint32(reply, i);
        
        break;

    default:
        fprintf(stderr, "unknown code %d\n", txn->code);
        return -1;
    }

    return 0;
}


int test_server_handler(struct binder_state *bs,
                   struct binder_transaction_data *txn,
                   struct binder_io *msg,
                   struct binder_io *reply)
{
    int (*handler)(struct binder_state *bs,
                   struct binder_transaction_data *txn,
                   struct binder_io *msg,
                   struct binder_io *reply);

    handler = (int (*)(struct binder_state *bs,
                   struct binder_transaction_data *txn,
                   struct binder_io *msg,
                   struct binder_io *reply))txn->target.ptr;
    
    return handler(bs, txn, msg, reply);
}

int main(int argc, char **argv)
{
    int fd;
    struct binder_state *bs;
    uint32_t svcmgr = BINDER_SERVICE_MANAGER;
    uint32_t handle;
    int ret;

    bs = binder_open(128*1024);
    if (!bs) {
        fprintf(stderr, "failed to open binder driver\n");
        return -1;
    }

    /* add service */
    ret = svcmgr_publish(bs, svcmgr, "hello", hello_service_handler); //第三个参数值需要唯一，obj->binder = (uintptr_t)ptr;
    if (ret) {
        fprintf(stderr, "failed to publish hello service\n");
        return -1;
    }
    ret = svcmgr_publish(bs, svcmgr, "goodbye", goodbye_service_handler);
    if (ret) {
        fprintf(stderr, "failed to publish goodbye service\n");
    }

    binder_set_maxthreads(bs, 10);
    
    /* //binder_loop已封装如下步骤：
    while (1)
    {
        /* read data */
        /* parse data, and process */
        /* reply */
    }
    */
    binder_loop(bs, test_server_handler); //通过函数test_server_handler处理消息

    return 0;
}

test_server.h :

#ifndef _TEST_SERVER_H
#define _TEST_SERVER_H

#define HELLO_SVR_CMD_SAYHELLO     1
#define HELLO_SVR_CMD_SAYHELLO_TO  2

#define GOODBYE_SVR_CMD_SAYGOODBYE     1
#define GOODBYE_SVR_CMD_SAYGOODBYE_TO  2

#endif // _TEST_SERVER_H

 

　　  2.编写test_client.c获得/使用服务：

/* Copyright 2008 The Android Open Source Project
 */

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <linux/types.h>
#include<stdbool.h>
#include <string.h>

#include <private/android_filesystem_config.h>

#include "binder.h"
#include "test_server.h"



uint32_t svcmgr_lookup(struct binder_state *bs, uint32_t target, const char *name)
{
    uint32_t handle;
    unsigned iodata[512/4];
    struct binder_io msg, reply;

    bio_init(&msg, iodata, sizeof(iodata), 4);
    bio_put_uint32(&msg, 0);  // strict mode header
    bio_put_string16_x(&msg, SVC_MGR_NAME);
    bio_put_string16_x(&msg, name);

    if (binder_call(bs, &msg, &reply, target, SVC_MGR_CHECK_SERVICE))
        return 0;

    handle = bio_get_ref(&reply);

    if (handle)
        binder_acquire(bs, handle);

    binder_done(bs, &msg, &reply);

    return handle;
}


struct binder_state *g_bs;
uint32_t g_hello_handle;
uint32_t g_goodbye_handle;

void sayhello(void)
{
    unsigned iodata[512/4];
    struct binder_io msg, reply;

    /* 构造binder_io */
    bio_init(&msg, iodata, sizeof(iodata), 4);
    bio_put_uint32(&msg, 0);  // strict mode header ,传入0
    bio_put_string16_x(&msg, "IHelloService");

    /* 放入参数 */

    /* 调用binder_call */
    if (binder_call(g_bs, &msg, &reply, g_hello_handle, HELLO_SVR_CMD_SAYHELLO))
        return ;
    
    /* 从reply中解析出返回值 */

    binder_done(g_bs, &msg, &reply);
    
}

/*
*带参数
*/
int sayhello_to(char *name)
{
    unsigned iodata[512/4];
    struct binder_io msg, reply;
    int ret;
    int exception;

    /* 构造binder_io */
    bio_init(&msg, iodata, sizeof(iodata), 4);
    bio_put_uint32(&msg, 0);  // strict mode header
    bio_put_string16_x(&msg, "IHelloService");

    /* 放入参数 */
    bio_put_string16_x(&msg, name);

    /* 调用binder_call */
    if (binder_call(g_bs, &msg, &reply, g_hello_handle, HELLO_SVR_CMD_SAYHELLO_TO))
        return 0;
    
    /* 从reply中解析出返回值 */
    exception = bio_get_uint32(&reply);
    if (exception)
        ret = -1;
    else
        ret = bio_get_uint32(&reply);

    binder_done(g_bs, &msg, &reply);

    return ret;
    
}


void saygoodbye(void)
{
    unsigned iodata[512/4];
    struct binder_io msg, reply;

    /* 构造binder_io */
    bio_init(&msg, iodata, sizeof(iodata), 4);
    bio_put_uint32(&msg, 0);  // strict mode header
    bio_put_string16_x(&msg, "IGoodbyeService");

    /* 放入参数 */

    /* 调用binder_call */
    if (binder_call(g_bs, &msg, &reply, g_goodbye_handle, GOODBYE_SVR_CMD_SAYGOODBYE))
        return ;
    
    /* 从reply中解析出返回值 */

    binder_done(g_bs, &msg, &reply);
    
}

int saygoodbye_to(char *name)
{
    unsigned iodata[512/4];
    struct binder_io msg, reply;
    int ret;
    int exception;

    /* 构造binder_io */
    bio_init(&msg, iodata, sizeof(iodata), 4);
    bio_put_uint32(&msg, 0);  // strict mode header
    bio_put_string16_x(&msg, "IGoodbyeService");

    /* 放入参数 */
    bio_put_string16_x(&msg, name);

    /* 调用binder_call */
    if (binder_call(g_bs, &msg, &reply, g_goodbye_handle, GOODBYE_SVR_CMD_SAYGOODBYE_TO))
        return 0;
    
    /* 从reply中解析出返回值 */
    exception = bio_get_uint32(&reply);
    if (exception)
        ret = -1;
    else
        ret = bio_get_uint32(&reply);

    binder_done(g_bs, &msg, &reply);

    return ret;
    
}



/* ./test_client hello
 * ./test_client hello <name>
 */

int main(int argc, char **argv)
{
    int fd;
    struct binder_state *bs;
    uint32_t svcmgr = BINDER_SERVICE_MANAGER;
    uint32_t handle;
    int ret;

    if (argc < 2){
        fprintf(stderr, "Usage:\n");
        fprintf(stderr, "%s <hello|goodbye>\n", argv[0]);
        fprintf(stderr, "%s <hello|goodbye> <name>\n", argv[0]);
        return -1;
    }

    bs = binder_open(128*1024);
    if (!bs) {
        fprintf(stderr, "failed to open binder driver\n");
        return -1;
    }
    g_bs = bs;


    /* get service */
    handle = svcmgr_lookup(bs, svcmgr, "goodbye");
    if (!handle) {
        fprintf(stderr, "failed to get goodbye service\n");
        return -1;
    }
    g_goodbye_handle = handle;
    fprintf(stderr, "Handle for goodbye service = %d\n", g_goodbye_handle);

    handle = svcmgr_lookup(bs, svcmgr, "hello");
    if (!handle) {
        fprintf(stderr, "failed to get hello service\n");
        return -1;
    }
    g_hello_handle = handle;
    fprintf(stderr, "Handle for hello service = %d\n", g_hello_handle);

    /* send data to server */
    if (!strcmp(argv[1], "hello"))
    {
        if (argc == 2) {
            sayhello();
        } else if (argc == 3) {
            ret = sayhello_to(argv[2]);
            fprintf(stderr, "get ret of sayhello_to = %d\n", ret);        
        }
    } else if (!strcmp(argv[1], "goodbye"))
    {
        if (argc == 2) {
            saygoodbye();
        } else if (argc == 3) {
            ret = saygoodbye_to(argv[2]);
            fprintf(stderr, "get ret of sayhello_to = %d\n", ret);        
        }
    }

    binder_release(bs, handle);

    return 0;
}

　　3.编译脚本：

　　（1）Makefile

APPS = service_manager test_client test_server

all : $(APPS)

service_manager : service_manager.o binder.o
    arm-linux-gcc -o $@ $^ -lpthread

test_client : test_client.o binder.o
    arm-linux-gcc -o $@ $^ -lpthread

test_server : test_server.o binder.o
    arm-linux-gcc -o $@ $^ -lpthread

%.o : %.c 
    arm-linux-gcc -DBINDER_IPC_32BIT=1 -I include -c -o $@ $<
            
clean:
    rm $(APPS) -f; rm -f *.o

　　（2）Android.mk

LOCAL_PATH:= $(call my-dir)

include $(CLEAR_VARS)

LOCAL_CFLAGS += -DBINDER_IPC_32BIT=1
 
LOCAL_SRC_FILES:= service_manager.c binder.c

LOCAL_C_INCLUDES += system/core/include/cutils

LOCAL_MODULE:= service_manager_my

include $(BUILD_EXECUTABLE)

include $(CLEAR_VARS)

LOCAL_CFLAGS += -DBINDER_IPC_32BIT=1

LOCAL_SRC_FILES:= test_server.c binder.c

LOCAL_C_INCLUDES += system/core/include/cutils

LOCAL_MODULE:= test_server

include $(BUILD_EXECUTABLE)

include $(CLEAR_VARS)

LOCAL_CFLAGS += -DBINDER_IPC_32BIT=1

LOCAL_SRC_FILES:= test_client.c binder.c

LOCAL_C_INCLUDES += system/core/include/cutils

LOCAL_MODULE:= test_client

include $(BUILD_EXECUTABLE)

 

-end-