3. 任意进程间通信(socketpair_binder)
进程每执行一次open打开文件，都会在内核中有一个file结构体表示它；
对每一个进程在内核中都会有一个task_struct表示进程，这个结构体内部有个files_struct结构体，这个结构体里面有个fdtble结构体，这个结构体里有个struct file **fd，fd就是个数组，fd[open时返回的句柄]就保存的对应文件的file结构体
因此不同进程的文件句柄只在本进程中有含义，如果想要在进程外面使用这个文件句柄，需要让外面进程的fd[任何句柄都可以]指向需要获得的目的进程的file
这里使用binder来传输文件句柄：
(1)APP1 open(file)得到fd1；
(2)通过binder驱动，根据fd1得到file：files->fdt->fd[fd1]
(3)从APP2的files->fdt->fd取出空项fd2，让fd[fd2]指向该file
(4)APP1通过fd1,APP2通过fd2就可以访问同一个file文件了，fd1和fd2不一样
取出APP_0004_Binder_CPP_App V4来修改:
1、server
(1)test_server.cpp :fd = open("1.txt");
(2)BnHelloService.cpp:添加结果get_fd:把fd传给client
(3)IHelloService.h:添加get_fd接口
2、client
(1)test_client.cpp:fd=service->get_fd();read(fd,buf);printf
(2)BpHelloService:添加get_fd向server发请求
IHelloService.h:(参考：IMediaPlayerService.h)
ifndef ANDROID_IHELLOERVICE_H
#define ANDROID_IHELLOERVICE_H
................头文件..................
#define HELLO_SVR_CMD_SAYHELLO 1
#define HELLO_SVR_CMD_SAYHELLO_TO 2
#define HELLO_SVR_CMD_GET_FD 3
namespace android{
class IHelloService:public IInterface
{
public:
DECLARE_META_INTERFACE(HelloService);
virtual void sayhello(void) = 0;
virtual int sayhello_to(const char *name) = 0;
virtual int get_fd(void) = 0;
};
class BnHelloService:public BnInterface<IHelloService>
{
private:
int fd;
public:
virtual status_t onTransact(uint32_t code,const Parcel& data,Parcel* reply,uint32_t flags = 0);
virtual void sayhello(void);
virtual int sayhello_to(const char *name);
virtual int get_to(void);
BnHelloService();
BnHelloService(int fd);
}
}
#endfi
BnHelloService.cpp(参考：IMediaPlayerService.cpp)
#include LOG_TAG "HelloService"
#include "IHelloService.h"
namespace android{
BnHelloService::BnHelloService()
{
}
BnHelloService::BnHelloService(int fd)
{
this->fd = fd;
}
status_t BnHelloService::onTransact(uint32_t code,const Parcel& data,Parcel* reply,uint32_t flags)
{
//解析数据，调用sayhello/sayhello_to
switch(code){
case HELLO_SVR_CMD_SAYHELLO:{
sayhello();
return NO_ERROR;
}break;
case HELLO_SVR_CMD_SAYHELLO_TO:{
//从data中取出参数
int32_t policy = data->readInt32();//把四字节的全零数据读出来
String16 name16 =data->readString16();
String8 name8(name16);
int cnt = sayhello_to(name8.string());
//把返回值写入reply传回去
reply->writeInt32(cnt);
return NO_ERROR;
}break;
case HELLO_SVR_CMD_GET_FD :{
int fd = this->get_fd();
reply->writeInt32(cnt);
/*
参考frameworksasecorejniandroid_view_InputChannel.cpp 里面的android_view_InputChannel_nativeWriteToParcel函数
*/
reply->writeDupFileDescriptor(fd);//这里使用writeDupFile....的原因是reply在析构的时候会close(fd),所以需要dup复制出一个同样的fd让其去close，而不会影响client使用该文件
return NO_ERROR;
}break;
default:
return BBinder::onTransact(code,data,reply,flags);
}
}
void BnHelloService::sayhello(void);
{
static int cnt = 0;
ALOGI("say hello : %d
", ++cnt);}
int BnHelloService::sayhello_to(const char *name);
{
static int cnt = 0; ALOGI("say hello to %s : %d
", name, ++cnt); return cnt;}
int BnHelloService::sayhello_to(const char *name);
{
static int cnt = 0; ALOGI("say hello to %s : %d
", name, ++cnt); return cnt;}
int BnHelloService::get_fd(void);
{
return fd;
}
}
BpHelloService.cpp(参考：IMediaPlayerService.cpp)
#include "IHelloService.h"
class BpHelloService:public BpInterface<IHelloService>
{
public:
BpHelloService(const sp<IBinder>& impl):BpInterface<IHelloService>(impl)
{
}
void sayhello(void)
{
//构造/发送数据
Parcel data,reply;
data.writeInt32(0);//data数据域可以自己定义，这里是为了统一
remote()->transact(HELLO_SVR_CMD_SAYHELLO,data,&reply);
}
void sayhello_to(const char *name)
{
//构造/发送数据
Parcel data,reply;
int exception;
data.writeInt32(0);//data数据域可以自己定义，这里是为了统一
data.writeString16(String16("IHelloService"));
data.writeString16(String16(name));
remote()->transact(HELLO_SVR_CMD_SAYHELLO_TO,data,&reply);
exception = reply.readInt32();
if(exception)
return -1;
else
return reply.readInt32();
}
int get_fd(void)
{
//构造/发送数据
Parcel data,reply;
int exception;
data.writeInt32(0);//data数据域可以自己定义，这里是为了统一
data.writeString16(String16("IHelloService"));
remote()->transact(HELLO_SVR_GET_FD,data,&reply);
exception = reply.readInt32();
if(exception)
return -1;
else{
int rawFd=reply.readFileDescriptor();
return dup(rawFd);//dup会复制一个fd，即有两个fd指向同一个文件，当函数退出的时候，reply被析构，会close(rawFd),而我们通过dup继续保持文件的fd，这样就不会影响对文件的访问
}
}
}
IMPLEMENT_META_INTERFACE(HelloService,"android.meida.In");
}
test_server.cpp(参考：Main_mediaserver.cpp)
#define LOG_TAG “HelloService”
#include "IHelloService.h"
.................头文件.......................
using namespace android;
/*usage:test_server <file>*/
int main(void)
{
int fd;
if(argc == 2)
fd = open(argv[1],O_RDWR);
//add service //while(1){read data,解析数据,调用服务函数}
//打开驱动，mmap
sp<ProcessState> proc(ProcessState::self());
//获得BpServiceManager
sp<IServiceManager> sm = defaultServiceManager();
sm->addService(String16("hello"),new BnHelloService(fd));
//循环体
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
return 0;
}
test_client.cpp
#define LOG_TAG “HelloService”
#include "IHelloService.h"
.................头文件.......................
using namespace android;
void main(int argc,char **argv)
{
int cnt; if (argc < 2){ ALOGI("Usage:
"); ALOGI("%s hello
", argv[0]);ALOGI("%s <readfile>
", argv[0]); ALOGI("%s hello <name>
", argv[0]); return -1; }//打开驱动，mmap
sp<ProcessState> proc(ProcessState::self());
//获得BpServiceManager
sp<IServiceManager> sm = defaultServiceManager();
if(strcmp(arfv[1],"hello") == 0)
{
sp<IBinder> binder = sm->getService(String16("hello"));
if(binder == 0)
{
ALOGI("can't get hello service ");
return -1;
}
//service肯定是BpHelloService指针
sp<IHelloService> service = interface_cast<IHelloService>(binder);
//调用Service函数
if(argc < 3){
service->sayhello();
ALOGI("client call sayhello");
}
else{
cnt = service->sayhello_to(argv[2]);
ALOGI("client call sayhello_to,cnt = %d ",cnt);
}
}
else if(strcmp(arfv[1],"readfile") == 0)
{
sp<IBinder> binder = sm->getService(String16("hello"));
if(binder == 0)
{
ALOGI("can't get hello service ");
return -1;
}
//service肯定是BpHelloService指针
sp<IHelloService> service = interface_cast<IHelloService>(binder);
//调用Service函数
int fd = service->get_fd();
lseek(fd,0,SEEK_SET);//移动文件指针，指向头部，否则不能重复读，因为读一次都文件指针一道最后面了，这个时候读数据为空，只能在写入后读取
char buf[500];
int len = read(fd,buf,500);
buf[len] = ' ';
ALOGI("client call get_fd= %d ",fd);
ALOGI("client read file:%s ",buf);
}
return 0;
}
参考代码:
frameworksasecorejniandroid_view_InputChannel.cpp (用binder传文件句柄)
server端写fd: android_view_InputChannel_nativeWriteToParcel
parcel->writeDupFileDescriptor
client端读fd: android_view_InputChannel_nativeReadFromParcel
int rawFd = parcel->readFileDescriptor();
int dupFd = dup(rawFd);
frameworks
ativelibsinderParcel.cpp
支持传输文件句柄的程序 v5:
第一次:
git clone https://github.com/weidongshan/APP_0004_Binder_CPP_App.git
更新:
git pull origin
取出指定版本:
git checkout v5 // v5, use binder to transfer file descriptor
编译:
把 APP_0004_Binder_CPP_App 放入 /work/android-5.0.2/frameworks/testing
cd /work/android-5.0.2/
. setenv
lunch //选择单板
mmm frameworks/testing/APP_0004_Binder_CPP_App
cp /work/android-5.0.2/out/target/product/tiny4412/system/bin/test_* /work/nfs_root/android_fs/
测试:
su
busybox mount -t nfs -o nolock,vers=2 192.168.1.123:/work/nfs_root /mnt
logcat HelloService:* GoodbyeService:* TestService:* *:S &
echo asfsdfasdf > 1.txt
./test_server 1.txt &
./test_client readfile
通过ls -l /proc/进程号/fd 可以查看文件fd指向的文件 比如：3 -> /mnt/android_fs/1.txt