android7.1.2啟動流程分析之init程式
闆子平台ROC_RK3328_CC
安卓源碼樹Android7.1.2–>kernel/init/main.c 檔案
asmlinkage void __init start_kernel(void){
rest_init();//在start_kernel函數最後一行
}
安卓源碼樹Android7.1.2–>kernel/init/main.c 檔案
static noinline void __init_refok rest_init(void)
{
kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
}
安卓源碼樹Android7.1.2–>kernel/init/main.c 檔案
static int __ref kernel_init(void unused)
{
kernel_init_freeable();//有ramdisk_execute_command = “/init”;
/ need to finish all async __init code before freeing the memory */
async_synchronize_full();
free_initmem();
mark_rodata_ro();
system_state = SYSTEM_RUNNING;
numa_default_policy();
flush_delayed_fput();
if (ramdisk_execute_command) {
if (!run_init_process(ramdisk_execute_command))
return 0;
pr_err("Failed to execute %s\n", ramdisk_execute_command);
}
if (execute_command) {
if (!run_init_process(execute_command))
return 0;
pr_err("Failed to execute %s. Attempting defaults...\n",
execute_command);
}
if (!run_init_process("/sbin/init") ||
!run_init_process("/etc/init") ||
!run_init_process("/bin/init") ||
!run_init_process("/bin/sh"))
return 0;
panic("No init found. Try passing init= option to kernel. "
"See Linux Documentation/init.txt for guidance.");
}
安卓系統跟目錄下的init.rc初始化腳本配置檔案預設放置在android源碼樹的system/core/rootdir目錄(類同于傳統linux系統下使用busybox生成的/sbin/init程式去解析/etc/inittab檔案)
android中的/init程式會通過解析/init.rc和init.rc裡面包含的
import /init.${ro.hardware}.rc這兩個檔案中的相關的指令來完成相應的初始化流程，是目前android系統運作時所依賴的相關硬體平台的名字，/proc/cmdline指令行腳本有androidboot.hardware=rk30board,此處的ro.hardware應該就是rk30board
/init.rc初始化腳本配置檔案是提供通用的相關初始化指令,/init..rc腳本配置檔案是提供特定的硬體平台的機器相關的初始化指令
init.rc初始化配置腳本的語言文法規則 有說明文檔android源碼樹system/core/init/readme.txt.
當平台啟動時，kernel中的引導參數将會被設定成init=/init.進而當挂載檔案系統成功後，便會開始執行/init初始化程式。init的入口點在源碼樹的system/core/init/init.cpp的main函數
int main(int argc, char** argv) {
//建立我們需要的基礎檔案系統/dev,/dev/pts,/dev/socket,/proc,/sys到initramdisk中的根目錄，然後由*.rc腳本配置檔案來解決餘下的目錄節點的建立
// 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.
if (is_first_stage) {
mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755");
mkdir("/dev/pts", 0755);
mkdir("/dev/socket", 0755);
mount("devpts", "/dev/pts", "devpts", 0, NULL);
#define MAKE_STR(x) __STRING(x)
mount("proc", "/proc", "proc", 0, "hidepid=2,gid=" MAKE_STR(AID_READPROC));
mount("sysfs", "/sys", "sysfs", 0, NULL);
}
NOTICE(“init %s started!\n”, is_first_stage ? “first stage” : “second stage”);
if (!is_first_stage) {
//此處是init: init second stage started!
// Indicate that booting is in progress to background fw loaders, etc.
close(open("/dev/.booting", O_WRONLY | O_CREAT | O_CLOEXEC, 0000));
property_init();
// If arguments are passed both on the command line and in DT,
// properties set in DT always have priority over the command-line ones.
///操作proc/device-tree/firmware/android裡面的裝置樹描述
process_kernel_dt();
//跟蹤進去，發現是操作/proc/cmdline裡面的核心指令行參數資訊的
process_kernel_cmdline();
// Propagate the kernel variables to internal variables
// used by init as well as the current required properties.
export_kernel_boot_props();
//add by xzj to set ro.rk.soc read from /proc/cpuinfo if not set
set_soc_if_need();
}
// If we're in the kernel domain, re-exec init to transition to the init domain now
// that the SELinux policy has been loaded.
if (is_first_stage) {
if (**restorecon("/init")** == -1) {
ERROR("restorecon failed: %s\n", strerror(errno));
security_failure();
}
char* path = argv[0];
char* args[] = { path, const_cast("--second-stage"), nullptr };
if (execv(path, args) == -1) {
ERROR("execv(\"%s\") failed: %s\n", path, strerror(errno));
security_failure();
}
}
// 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.
NOTICE("Running restorecon...\n");
restorecon("/dev");
restorecon("/dev/socket");
restorecon("/dev/__properties__");
restorecon("/property_contexts");
restorecon_recursive("/sys");
epoll_fd = epoll_create1(EPOLL_CLOEXEC);
if (epoll_fd == -1) {
ERROR("epoll_create1 failed: %s\n", strerror(errno));
exit(1);
}
signal_handler_init();
property_load_boot_defaults();
export_oem_lock_status();
start_property_service();
const BuiltinFunctionMap function_map;
Action::set_function_map(&function_map);
Parser& parser = Parser::GetInstance();
parser.AddSectionParser("service",std::make_unique());
parser.AddSectionParser("on", std::make_unique());
parser.AddSectionParser("import", std::make_unique());
//解析/init.rc配置檔案
parser.ParseConfig("/init.rc");
ActionManager& am = ActionManager::GetInstance();
//周遊連結清單并執行所有标志為early-init的活動Action
am.QueueEventTrigger("early-init");
// Queue an action that waits for coldboot done so we know ueventd has set up all of /dev...
am.QueueBuiltinAction(wait_for_coldboot_done_action, "wait_for_coldboot_done");
// ... so that we can start queuing up actions that require stuff from /dev.
am.QueueBuiltinAction(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");
am.QueueBuiltinAction(set_mmap_rnd_bits_action, "set_mmap_rnd_bits");
am.QueueBuiltinAction(keychord_init_action, "keychord_init");
am.QueueBuiltinAction(console_init_action, "console_init");
// Trigger all the boot actions to get us started.
am.QueueEventTrigger("init");
// Repeat mix_hwrng_into_linux_rng in case /dev/hw_random or /dev/random
// wasn't ready immediately after wait_for_coldboot_done
am.QueueBuiltinAction(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");
// Don't mount filesystems or start core system services in charger mode.
std::string bootmode = property_get("ro.bootmode");
if (bootmode == "charger") {
am.QueueEventTrigger("charger");
} else {
am.QueueEventTrigger("late-init");
}
// Run all property triggers based on current state of the properties.
am.QueueBuiltinAction(queue_property_triggers_action, "queue_property_triggers");
while (true) {
if (!waiting_for_exec) {
am.ExecuteOneCommand();
restart_processes();
}
return 0;
}
/proc/cmdline 檔案裡資訊如下
earlyprintk=uart8250-32bit,0xff130000 console=ttyFIQ0 androidboot.baseband=N/A androidboot.selinux=permissive androidboot.hardware=rk30board androidboot.console=ttyFIQ0 init=/init mtdparts=rk29xxnand:[email protected](uboot),[email protected](trust),[email protected](misc),[email protected](baseparamer),[email protected](resource),[email protected](kernel),[email protected](boot),[email protected]