QCOM FFBM 模式启动流程梳理

名词解释

FFBM: Fast Factory Boot Mode
提供了一种Linux系统最小UI交互界面的设计参考方式

Kernel FFBM 启动流程图

Kernel FFBM 启动步骤解析

1. boot mode参数解析

   通过process_kernel_cmdline，解析”/proc/cmdline”, 如果有”androidboot.” 关键字，则设置ro.bootmode

2. 根据ro.bootmode，做event trigger

   std::string bootmode = property_get("ro.bootmode");
if (bootmode == "charger") {
am.QueueEventTrigger("charger");
} else if (strncmp(bootmode.c_str(), "ffbm", 4) == 0) {
NOTICE("Booting into ffbm mode\n");
am.QueueEventTrigger("ffbm");
} else {
am.QueueEventTrigger("late-init");
}

3. 根据ro.bootmode，判断是否启动zygote

   static int queue_fs_event(int code) {
int ret = code;
std::string bootmode = property_get("ro.bootmode");
if (strncmp(bootmode.c_str(), "ffbm", 4) == 0) {
NOTICE("ffbm mode, not start class main\n");
return 0;
.......
}
   zygote 通过class_start main启动， 通过阻止nonencrypted的trigger，达到不启动zygote的目的

4. ffbm service

   做最小系统的启动
   on ffbm
trigger early-fs
trigger factory-fs
trigger fs
trigger post-fs
trigger load_system_props_action
trigger post-fs-data
trigger load_persist_props_action
trigger firmware_mounts_complete
trigger early-boot
trigger mmi