android开机启动流程说明
第一步：启动linux
1.Bootloader
2.Kernel
第二步android系统启动：入口为init.rc(system\core\rootdir)
1./system/bin/service manager: Binder 守护进程；
2.Runtime;
3.Zygote :app-process/app-main;
4.Start VM;
5.Start server
6.Start android service:Register to service Manager
7.Start Launcher
第三步：应用程序启动：运行package Manager
l Init进程
Android系统在启动时首先会启动Linux系统，引导加载Linux Kernel并启动init进程。Init进程是一个由内核启动的用户级进程，是Android系统的第一个进程。该进程的相关代码在platform\system\core\init\init.c。在main函数中，有如下代码：
open_devnull_stdio();
log_init();
INFO("reading config file\n");
init_parse_config_file("/init.rc");
/* pull the kernel commandline and ramdisk properties file in */
import_kernel_cmdline(0);
get_hardware_name(hardware, &revision);
snprintf(tmp, sizeof(tmp), "/init.%s.rc", hardware);
init_parse_config_file(tmp);
这里会加载解析init.rc和init.hardware.rc两个初始化脚本。*.rc文件定义了在init进程中需要启动哪些进程服务和执行哪些动作。其详细说明参见platform\system\core\init\reademe.txt。init.rc见如下定义：
service servicemanager /system/bin/servicemanager
user system
critical
onrestart restart zygote
onrestart restart media
service vold /system/bin/vold
socket vold stream 0660 root mount
ioprio be 2
service netd /system/bin/netd
socket netd stream 0660 root system
socket dnsproxyd stream 0660 root inet
service debuggerd /system/bin/debuggerd
service ril-daemon /system/bin/rild
socket rild stream 660 root radio
socket rild-debug stream 660 radio system
user root
group radio cache inet misc audio sdcard_rw
service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
socket zygote stream 666
onrestart write /sys/android_power/request_state wake
onrestart write /sys/power/state on
onrestart restart media
onrestart restart netd
service drm /system/bin/drmserver
user drm
group system root inet
具体解析过程见platform\system\core\init\Init_parser.c。解析所得服务添加到service_list中，动作添加到action_list中。
接下来在main函数中执行动作和启动进程服务：
execute_one_command();
restart_processes()
通常init过程需要创建一些系统文件夹并启动USB守护进程、Android Debug Bridge守护进程、Debug守护进程、ServiceManager进程、Zygote进程等。
l ServiceManager进程
ServiceManager进程是所有服务的管理器。由init.rc对ServiceManager的描述service servicemanager /system/bin/servicemanager可知servicemanager进程从platform\frameworks\base\cmd\servicemanager\Service_manager.cpp启动。在main函数中有如下代码：
int main(int argc, char **argv)
{
struct binder_state *bs;
void *svcmgr = BINDER_SERVICE_MANAGER;
bs = binder_open(128*1024);
if (binder_become_context_manager(bs)) {
LOGE("cannot become context manager (%s)\n", strerror(errno));
return -1;
}
svcmgr_handle = svcmgr;
binder_loop(bs, svcmgr_handler);
return 0;
}
首先调用binder_open()打开Binder设备(/dev/binder)，调用binder_become_context_manager()把当前进程设置为ServiceManager。ServiceManager本身就是一个服务。
int binder_become_context_manager(struct binder_state *bs)
{
return ioctl(bs->fd, BINDER_SET_CONTEXT_MGR, 0);
}
最后binder_loop()进入循环状态，并设置svcmgr_handler回调函数等待添加、查询、获取服务等请求。
l Zygote进程
Zygote进程用于产生其他进程。由init.rc对zygote的描述service zygot /system/bin/app_process可知zygote进程从platfrom\frameworks\base\cmds\app_process\App_main.cpp启动。在main函数中有如下代码：
if (0 == strcmp("--zygote", arg)) {
bool startSystemServer = (i < argc) ?
strcmp(argv[i], "--start-system-server") == 0 : false;
setArgv0(argv0, "zygote");
set_process_name("zygote");
runtime.start("com.android.internal.os.ZygoteInit",
startSystemServer);
} else {
set_process_name(argv0);
runtime.mClassName = arg;
// Remainder of args get passed to startup class main()
runtime.mArgC = argc-i;
runtime.mArgV = argv+i;
LOGV("App process is starting with pid=%d, class=%s.\n",
getpid(), runtime.getClassName());
runtime.start();
}
首先创建AppRuntime，即AndroidRuntime，建立了一个Dalvik虚拟机。通过这个runtime传递com.android.internal.os.ZygoteInit参数，从而由Dalvik虚拟机运行ZygoteInit.java的main()，开始
补充：移动开发 , Android ,
