Android知识总结

一、简介

用户空间中 binder_open(), binder_mmap(), binder_ioctl() 这些方法通过 system call 来调用内核空间 Binder 驱动中的方法。内核空间与用户空间共享内存通过 copy_from_user(), copy_to_user() 内核方法来完成用户空间与内核空间内存的数据传输。 Binder驱动中有一个全局的 binder_procs 链表保存了服务端的进程信息。

1.1、用户空间/内核空间

Kernel space 是 Linux 内核的运行空间，User space 是用户程序的运行空间。为了安全，它们是隔离的，即使用户的程序崩溃了，内核也不受影响。
Kernel space 可以执行任意命令，调用系统的一切资源； User space 只能执行简单的运算，不能直接调用系统资源，必须通过系统接口（又称 system call），才能向内核发出指令。

二、binder_init

Kconfig 配置文件

menu "Android"

config ANDROID
    bool "Android Drivers"
    ---help---
      Enable support for various drivers needed on the Android platform

if ANDROID

config ANDROID_BINDER_IPC
    bool "Android Binder IPC Driver"
    depends on MMU
    default n
    ---help---
      Binder is used in Android for both communication between processes,
      and remote method invocation.

      This means one Android process can call a method/routine in another
      Android process, using Binder to identify, invoke and pass arguments
      between said processes.

//binder 配置信息 
config ANDROID_BINDER_DEVICES
    string "Android Binder devices"
    depends on ANDROID_BINDER_IPC
    default "binder"
    ---help---
      Default value for the binder.devices parameter.

      The binder.devices parameter is a comma-separated list of strings
      that specifies the names of the binder device nodes that will be
      created. Each binder device has its own context manager, and is
      therefore logically separated from the other devices.

config ANDROID_BINDER_IPC_32BIT
    bool
    depends on !64BIT && ANDROID_BINDER_IPC
    default y
    ---help---
      The Binder API has been changed to support both 32 and 64bit
      applications in a mixed environment.

      Enable this to support an old 32-bit Android user-space (v4.4 and
      earlier).

      Note that enabling this will break newer Android user-space.

endif # if ANDROID

endmenu

kernel/drivers/staging/android/binder.c

//结构体中记录把 native层的方法对应驱动层的方法
static const struct file_operations binder_fops = {
        //native层 <==> 驱动层
    .owner = THIS_MODULE,
    .poll = binder_poll,
    .unlocked_ioctl = binder_ioctl,
    .compat_ioctl = binder_ioctl,
    .mmap = binder_mmap,
    .open = binder_open,
    .flush = binder_flush,
    .release = binder_release,
};

static int __init init_binder_device(const char *name){
    int ret;
    struct binder_device *binder_device;
    //为binder设备分配内存
    binder_device = kzalloc(sizeof(*binder_device), GFP_KERNEL);
    //初始化设备
    // 设备的文件操作结构，这是file_operations结构
    binder_device->miscdev.fops = &binder_fops; 
    // 次设备号 动态分配
    binder_device->miscdev.minor = MISC_DYNAMIC_MINOR; 
    // 设备名,"binder"
    binder_device->miscdev.name = name; 
    //INVALID_UID是无效的，主要保存AMS传过来的 UID
    binder_device->context.binder_context_mgr_uid = INVALID_UID;
    binder_device->context.name = name;
    //misc驱动注册
    ret = misc_register(&binder_device->miscdev);
    //将hlist节点添加到binder_devices为表头的设备链表
    hlist_add_head(&binder_device->hlist, &binder_devices);
    return ret;
}