Android 根文件系统启动分析

核心提示：action_for_each_trigger("init", action_add_queue_tail); drain_action_queue(); property_set_fd = start_property_service(); /* 为sigchld handler创建信号机制*/

action_for_each_trigger("init", action_add_queue_tail); drain_action_queue(); property_set_fd = start_property_service(); /* 为sigchld handler创建信号机制*/ if (socketpair(AF_UNIX, SOCK_STREAM, 0, s) == 0) { signal_fd = s[0]; signal_recv_fd = s[1]; fcntl(s[0], F_SETFD, FD_CLOEXEC); fcntl(s[0], F_SETFL, O_NONBLOCK); fcntl(s[1], F_SETFD, FD_CLOEXEC); fcntl(s[1], F_SETFL, O_NONBLOCK); } /* 确认所有初始化工作完成 * device_fd(device init 完成) * property_set_fd(property server start 完成) * signal_recv_fd (信号机制建立) */ if ((device_fd < 0) || (property_set_fd < 0) || (signal_recv_fd < 0)) { ERROR("init startup failure "); return 1; } /* execute all the boot actions to get us started */ action_for_each_trigger("early-boot", action_add_queue_tail); action_for_each_trigger("boot", action_add_queue_tail); drain_action_queue(); /* run all property triggers based on current state of the properties */ queue_all_property_triggers(); drain_action_queue(); /* enable property triggers */ property_triggers_enabled = 1; /* * 注册轮询事件: * - device_fd * - property_set_fd * -signal_recv_fd * -如果有keychord，则注册keychord_fd */ ufds[0].fd = device_fd; ufds[0].events = POLLIN; ufds[1].fd = property_set_fd; ufds[1].events = POLLIN; ufds[2].fd = signal_recv_fd; ufds[2].events = POLLIN; fd_count = 3; if (keychord_fd > 0) { ufds[3].fd = keychord_fd; ufds[3].events = POLLIN; fd_count++; } else { ufds[3].events = 0; ufds[3].revents = 0; }/*如果支持BOOTCHART,则初始化BOOTCHART*/#if BOOTCHART bootchart_count = bootchart_init(); if (bootchart_count < 0) { ERROR("bootcharting init failure "); } else if (bootchart_count > 0) { NOTICE("bootcharting started (period=%d ms) ", bootchart_count*BOOTCHART_POLLING_MS); } else { NOTICE("bootcharting ignored "); }#endif /* *进入主进程循环: * - 重置轮询事件的接受状态，revents为0 * - 查询action队列并执行。 * - 重启需要重启的服务 * - 轮询注册的事件 * - 如果signal_recv_fd的revents为POLLIN，则得到一个信号，获取并处理 * -