android启动分析.docx

init.c分析因为启动是首先运行init.c所以从其main()开始分析652 int main(int argc, char *argv)653 654 int fd_count = 0;655 struct pollfd ufds4;656 char *tmpdev;657 char* debuggable;658 char tmp32;659 int property_set_fd_init = 0;660 int signal_fd_init = 0;661 int keychord_fd_init = 0;662 663 if (!strcmp(basename(argv0), ueventd)664 return ueventd_main(argc, argv);这段代码初始化一些变量，然后663行判断是否给用户空间发事件，这里显然不执行if语句。666 /* clear the umask */667 umask(0);设置允许当前进程创建文件或者目录为最大可操作的权限。673 mkdir(/dev, 0755);674 mkdir(/proc, 0755);675 mkdir(/sys, 0755);创建设备目录dev，进程文件系统目录proc，系统目录sys。677 mount(tmpfs, /dev, tmpfs, 0, mode=0755);678 mkdir(/dev/pts, 0755);679 mkdir(/dev/socket, 0755);680 mount(devpts, /dev/pts, devpts, 0, NULL);681 mount(proc, /proc, proc, 0, NULL);682 mount(sysfs, /sys, sysfs, 0, NULL);把tmpfs挂载到/dev下，然后创建pts和socket目录，在/dev/pts挂装devpts虚拟文件系统，在目录/proc挂装proc文件系统，在目录/sys挂装sysfs文件系统。690 open_devnull_stdio();创建空的设备节点（/dev/null）。691 log_init();创建kmsg(/dev/kmsg)节点，主要用来输出LOG信息。693 INFO(reading config filen);694 init_parse_config_file(/init.rc);分析根目录下面的init.rc配置文件，并且把里面的参数组成链表的方式697 import_kernel_cmdline(0);从内核里取得引导参数699 get_hardware_name(hardware, &revision);获取当前android系统运行的硬件信息。主要从/proc/cpuinfo里读到相关的信息。700 snprintf(tmp, sizeof(tmp), /init.%s.rc, hardware);701 init_parse_config_file(tmp);以/init.硬件名称.rc来获取相应硬件的配置文件，并且把配置文件参数加载到链表里。以下一段代码，用于加载action_list和queue_list列表，action_list用来加载脚本里的action,queue_list主要用于加载非脚本里的action以及排列action的顺序703 action_for_each_trigger(early-init, action_add_queue_tail);在action_list列表里查找以early-init为名的action变量，找到后将它加到queue_list列表里705 queue_builtin_action(wait_for_coldboot_done_action, wait_for_coldboot_done);把第一个（函数）和第二个参数（名字）组装成一个action变量加到action_list和queue_list列表。706 queue_builtin_action(property_init_action, property_init);707 queue_builtin_action(keychord_init_action, keychord_init);708 queue_builtin_action(console_init_action, console_init);console_init_action会加载开机画面和文字709 queue_builtin_action(set_init_properties_action, set_init_properties);711 /* execute all the boot actions to get us started */712 action_for_each_trigger(init, action_add_queue_tail);713 action_for_each_trigger(early-fs, action_add_queue_tail);714 action_for_each_trigger(fs, action_add_queue_tail);715 action_for_each_trigger(post-fs, action_add_queue_tail);716 717 queue_builtin_action(property_service_init_action, property_service_init);718 queue_builtin_action(signal_init_action, signal_init);719 queue_builtin_action(check_startup_action, check_startup);720 721 /* execute all the boot actions to get us started */722 action_for_each_trigger(early-boot, action_add_queue_tail);723 action_for_each_trigger(boot, action_add_queue_tail);724 725 /* run all property triggers based on current state of the properties */726 queue_builtin_action(queue_property_triggers_action, queue_propety_triggers);729 #if BOOTCHART730 queue_builtin_action(bootchart_init_action, bootchart_init);731 #endif这里没有定义BOOTCHART所以不执行这个733 for(;) 734 int nr, i, timeout = -1;735 736 execute_one_command();737 restart_processes();来判断那些服务需要重新启动。738 739 if (!property_set_fd_init & get_property_set_fd() 0) 740 ufdsfd_count.fd = get_property_set_fd();741 ufdsfd_count.events = POLLIN;742 ufdsfd_count.revents = 0;743 fd_count+;744 property_set_fd_init = 1;745 746 if (!signal_fd_init & get_signal_fd() 0) 747 ufdsfd_count.fd = get_signal_fd();748 ufdsfd_count.events = POLLIN;749 ufdsfd_count.revents = 0;750 fd_count+;751 signal_fd_init = 1;752 753 if (!keychord_fd_init & get_keychord_fd() 0) 754 ufdsfd_count.fd = get_keychord_fd();755 ufdsfd_count.events = POLLIN;756 ufdsfd_count.revents = 0;757 fd_count+;758 keychord_fd_init = 1;759 760 761 if (process_needs_restart) 762 timeout = (process_needs_restart - gettime() * 1000;763 if (timeout 0) 772 if (timeout BOOTCHART_POLLING_MS)773 timeout = BOOTCHART_POLLING_MS;774 if (bootchart_step() 0 | -bootchart_count = 0) 775 bootchart_finish();776 bootchart_count = 0;777 778 779 #endif这段代码是用来计算运行性能。780 781 nr = poll(ufds, fd_count, timeout);782 if (nr = 0)783 continue;轮询几个socket是否有事件处理。784785 for (i = 0; i fd_count; i+) 786 if (ufdsi.revents = POLLIN) 787 if (ufdsi.fd = get_property_set_fd