概述：
接在i.mx6 Android5.1.1 初始化流程之框架之后
参考资料：http://blog.csdn.net/mr_raptor/article/category/799879
相关源码： /system/core/init/
相关配置文件：/system/core/rootdir/
从下面全文可以得出：
1).init进程和其相关的文件init.rc、ueventd.rc是在ramdisk.img中
2).修改节点权限： /ueventd.rc /ueventd.Freescale.rc
3). 修改相关服务和创建文件：/init.rc
1. mian.c
关于代码中的属性服务，可以查看：i.mx6 Android5.1.1 系统属性
关于代码中的init.rc，可以查看： i.mx6 Android5.1.1 初始化流程之init.rc解析
int main(int argc, char **argv) { int fd_count = 0; struct pollfd ufds[4]; char *tmpdev; char* debuggable; char tmp[32]; int property_set_fd_init = 0; int signal_fd_init = 0; int keychord_fd_init = 0; bool is_charger = false; char watchdog[PROPERTY_MAX_VALUE]; int ret;
/*后面两个是初始化ueventd和看门狗，从上一章的ps中可以看出，这两个确实是进程init（PID=1）最初创建的两个进程*/
/*查看是否有看门狗的属性*/ ret = property_get("ro.boot.watchdogd", watchdog);
/*启动ueventd进程*/ if (!strcmp(basename(argv[0]), "ueventd")) return ueventd_main(argc, argv); if (!strcmp(basename(argv[0]), "watchdogd")) { if(ret && !(strcmp(watchdog, "disabled"))) { return 0; } else { return watchdogd_main(argc, argv); /*在这里启动看门狗*/ } } /* clear the umask */ umask(0); /* Get the basic filesystem setup we need put * together in the initramdisk on / and then we'll * let the rc file figure out the rest. */
/* 创建目录，挂在文件系统，给权限
* tmpfs ：/dev
* devpts ：/dev/pts
* proc ：/proc
* sysfs ：/sys
*/ mkdir("/dev", 0755); mkdir("/proc", 0755); mkdir("/sys", 0755); mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755"); mkdir("/dev/pts", 0755); mkdir("/dev/socket", 0755); mount("devpts", "/dev/pts", "devpts", 0, NULL); mount("proc", "/proc", "proc", 0, NULL); mount("sysfs", "/sys", "sysfs", 0, NULL); close(open("/dev/.booting", O_WRONLY | O_CREAT, 0000)); open_devnull_stdio(); //将标准输入、输出、错误定向到空 klog_init(); //将log重定向到/proc/kmsg当中 property_init(); //初始化属性服务,关于属性服务，可以查看：i.mx6 Android5.1.1 系统属性 get_hardware_name(hardware, &revision); //得到硬件信息和版本信息 get_soc_name(soc); //得到soc名字 process_kernel_cmdline(); // 设置基本属性 union selinux_callback cb; cb.func_log = log_callback; selinux_set_callback(SELINUX_CB_LOG, cb); cb.func_audit = audit_callback; selinux_set_callback(SELINUX_CB_AUDIT, cb); selinux_initialize(); /* These directories were necessarily created before initial policy load * and therefore need their security context restored to the proper value. * This must happen before /dev is populated by ueventd. */ restorecon("/dev"); restorecon("/dev/socket"); restorecon("/dev/__properties__"); restorecon_recursive("/sys"); is_charger = !strcmp(bootmode, "charger"); INFO("property init "); property_load_boot_defaults(); //加载/default.prop文件 进行默认属性配置相关的工作 INFO("reading config file "); init_parse_config_file("/init.rc"); //注意：解析/init.rc，并将所有元素加入链表，关于init.rc，可以查看：i.mx6 Android5.1.1 系统属性
/* 首先说明一下，在函数中对于init.rc命令的解析之后，将所有命令分类分别挂在了action_list,service_list,action_queue三个链表当中
* serevice_list:用于保存init.rc当中的service配置信息
* action_list： 用于保存从init.rc当中解析出来的所有action
* action_queue: 用于保存所有待执行的action
*
* 下面的两个函数action_for_each_trigger和queue_builtin_action
* action_for_each_trigger：将action加入到action_queue当中，表示正准备执行
* queue_builtin_action： 创建一个action，并将其挂在atcion_queue和action_list当中，
*/
action_for_each_trigger("early-init", action_add_queue_tail); //接着上面，把链表中为on early-init的元素提取执行。（我们没有）将early-init动作添加到链表action_queue中 queue_builtin_action(wait_for_coldboot_done_action, "wait_for_coldboot_done"); //创建wait_for_coldboot_done动作并添加到链表action_queue和action_list中，在这里注意action_list用于保存从init.rc中解析出来的所有Action,而action_queue却是用于保存待执行的Action，action_queue是一个待执行队列。 queue_builtin_action(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng"); queue_builtin_action(keychord_init_action, "keychord_init"); queue_builtin_action(console_init_action, "console_init"); /* execute all the boot actions to get us started */ action_for_each_trigger("init", action_add_queue_tail);//执行Init.rc中的on init（这个我们就有了），后面分析 /* Repeat mix_hwrng_into_linux_rng in case /dev/hw_random or /dev/random * wasn't ready immediately after wait_for_coldboot_done */ queue_builtin_action(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng"); queue_builtin_action(property_service_init_action, "property_service_init"); queue_builtin_action(signal_init_action, "signal_init"); /* Don't mount filesystems or start core system services if in charger mode. */ if (is_charger) { action_for_each_trigger("charger", action_add_queue_tail); //执行这个，不执行下面的 } else { action_for_each_trigger("late-init", action_add_queue_tail); } /* run all property triggers based on current state of the properties */ queue_builtin_action(queue_property_triggers_action, "queue_property_triggers"); #if BOOTCHART queue_builtin_action(bootchart_init_action, "bootchart_init"); #endif for(;;) { int nr, i, timeout = -1; execute_one_command(); //按序执行action_queue里的action restart_processes(); //重启一些关键进程，也就是守护进程 //添加，只执行一次 if (!property_set_fd_init && get_property_set_fd() > 0) { ufds[fd_count].fd = get_property_set_fd(); ufds[fd_count].events = POLLIN; ufds[fd_count].revents = 0; fd_count++; property_set_fd_init = 1; }
/*同上*/ if (!signal_fd_init && get_signal_fd() > 0) { ufds[fd_count].fd = get_signal_fd(); ufds[fd_count].events = POLLIN; ufds[fd_count].revents = 0; fd_count++; signal_fd_init = 1; }
/*同上*/ if (!keychord_fd_init && get_keychord_fd() > 0) { ufds[fd_count].fd = get_keychord_fd(); ufds[fd_count].events = POLLIN; ufds[fd_count].revents = 0; fd_count++; keychord_fd_init = 1; } //计算超时时间 if (process_needs_restart) { timeout = (process_needs_restart - gettime()) * 1000; if (timeout < 0) timeout = 0; } if (!action_queue_empty() || cur_action) timeout = 0; #if BOOTCHART if (bootchart_count > 0) { if (timeout < 0 || timeout > BOOTCHART_POLLING_MS) timeout = BOOTCHART_POLLING_MS; if (bootchart_step() < 0 || --bootchart_count == 0) { bootchart_finish(); bootchart_count = 0; } } #endif //监控句柄池中的事件，如果都没有变化，程序就停在这里了 nr = poll(ufds, fd_count, timeout); if (nr <= 0) continue; //对于监听到的事件进行处理 for (i = 0; i < fd_count; i++) { if (ufds[i].revents & POLLIN) { if (ufds[i].fd == get_property_set_fd()) handle_property_set_fd(); else if (ufds[i].fd == get_keychord_fd()) handle_keychord(); else if (ufds[i].fd == get_signal_fd()) handle_signal(); } } } return 0; }
小结：
1。启动ueventd和watchdogd进程
2。将标准输入，输出，错误定向到null
3.重定向log
4.初始化属性的区域
5.添加各种属性
6.解析init.rc
7.将init.rc中解析出来的行为进行分类保存，并再添加一些默认行为
8.进入循环守护
1). 执行action_queue中的action
2). 守护一些关键进程
3). 建立属性、信号、组合按键的监听。当有行为发生时，对其进行相应处理，没有则停滞在这里
从上诉程序可以分析出action的执行顺序为：
early-init ------------------>>init.rc
wait_for_coldboot_done
mix_hwrng_into_linux_rng
keychord_init
console_init
init ------------------>>init.rc
mix_hwrng_into_linux_rng
property_service_init
signal_init
charger或者late-init ------------------>>init.rc
queue_property_triggers
2. ueventd_main
int ueventd_main(int argc, char **argv) { struct pollfd ufd; int nr; char tmp[32]; /* * init sets the umask to 077 for forked processes. We need to * create files with exact permissions, without modification by * the umask. */ umask(000); /* Prevent fire-and-forget children from becoming zombies. * If we should need to wait() for some children in the future * (as opposed to none right now), double-forking here instead * of ignoring SIGCHLD may be the better solution. */ signal(SIGCHLD, SIG_IGN); open_devnull_stdio(); klog_init(); #if LOG_UEVENTS /* Ensure we're at a logging level that will show the events */ if (klog_get_level() < KLOG_INFO_LEVEL) { klog_set_level(KLOG_INFO_LEVEL); } #endif union selinux_callback cb; cb.func_log = log_callback; selinux_set_callback(SELINUX_CB_LOG, cb); INFO("starting ueventd "); /* Respect hardware passed in through the kernel cmd line. Here we will look * for androidboot.hardware param in kernel cmdline, and save its value in * hardware[]. */ import_kernel_cmdline(0, import_kernel_nv); get_hardware_name(hardware, &revision); //解析ueventd.rc和ueventd.fressale.rc ueventd_parse_config_file("/ueventd.rc"); snprintf(tmp, sizeof(tmp), "/ueventd.%s.rc", hardware); ueventd_parse_config_file(tmp); //设备初始化 device_init(); ufd.events = POLLIN; ufd.fd = get_device_fd(); while(1) { ufd.revents = 0; nr = poll(&ufd, 1, -1); //循环等待 if (nr <= 0) continue; if (ufd.revents & POLLIN) handle_device_fd(); //讲接收过来的信息进行处理 } }