android7.1.2启动流程分析之init程序
android7.1.2启动流程分析之init程序
板子平台ROC_RK3328_CC
安卓源码树Android7.1.2–>kernel/init/main.c 文件
asmlinkage void __init start_kernel(void){
/* Do the rest non-__init’ed, we’re now alive */
rest_init();//在start_kernel函数最后一行
}
安卓源码树Android7.1.2–>kernel/init/main.c 文件
static noinline void __init_refok rest_init(void)
{
/*
* We need to spawn init first so that it obtains pid 1, however
* the init task will end up wanting to create kthreads, which, if
* we schedule it before we create kthreadd, will OOPS.
*/
kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
}
安卓源码树Android7.1.2–>kernel/init/main.c 文件
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();
/*内核启动信息“Kernel command line: root=/dev/mtdblock4 rootfstype=yaffs2 rootflags=inband-tags console=ttyS0,115200n8 rdinit=/sbin/init ro mem=64M” 而我的android 7.1.2的板子里kernel comman line 里是init=/init
如果ramdisk_execute_command变量指定了要运行的程序，启动它。
ramdisk_execute_command的取值分为三种情况：
a.如果命令行参数中指定了“rdinit=…”，则ramdisk_execute_command等于这个参数指定的程序。
b.否则，如果/init程序存在，ramdisk_execute_command就等于/init
c.否则，ramdisk_execute_command为空
本main.c文件 kernel_init_freeable(void)函数有
if (!ramdisk_execute_command)
ramdisk_execute_command = "/init";
*/
if (ramdisk_execute_command) {
if (!run_init_process(ramdisk_execute_command))
return 0;
pr_err("Failed to execute %s\n", ramdisk_execute_command);
}
/*
* We try each of these until one succeeds.
*
* The Bourne shell can be used instead of init if we are
* trying to recover a really broken machine.
*/
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.");
}
安卓系统跟目录下的init.rc初始化脚本配置文件默认放置在android源码树的system/core/rootdir目录(类同于传统linux系统下使用busybox生成的/sbin/init程序去解析/etc/inittab文件)
android中的/init程序会通过解析/init.rc和init.rc里面包含的
import /init.${ro.hardware}.rc这两个文件中的相关的命令来完成相应的初始化流程，
/init.rc初始化脚本配置文件是提供通用的相关初始化指令,/init.
init.rc初始化配置脚本的语言语法规则 有说明文档android源码树system/core/init/readme.txt.
当平台启动时，kernel中的引导参数将会被设置成init=/init.从而当挂载文件系统成功后，便会开始执行/init初始化程序。init的入口点在源码树的system/core/init/init.cpp的main函数
int main(int argc, char** argv) {
//创建我们需要的基础文件系统/dev,/dev/pts,/dev/socket,/proc,/sys到initramdisk中的根目录，然后由*.rc脚本配置文件来解决余下的目录节点的创建
// 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) {
//此处是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里面的设备树描述
process_kernel_dt();
//跟踪进去，发现是操作/proc/cmdline里面的内核命令行参数信息的
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配置文件
parser.ParseConfig("/init.rc");
ActionManager& am = ActionManager::GetInstance();
//遍历链表并执行所有标志为early-init的活动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 文件里信息如下
earlyprintk=uart8250-32bit,0xff130000 console=ttyFIQ0 androidboot.baseband=N/A androidboot.selinux=permissive androidboot.hardware=rk30board androidboot.console=ttyFIQ0 init=/init mtdparts=rk29xxnand:0x00002000@0x00002000(uboot),0x00004000@0x00004000(trust),0x00002000@0x00008000(misc),0x00000800@0x0000A000(baseparamer),0x00007800@0x0000A800(resource),0x00010000@0x00012000(kernel),0x00010000@0x00022000(boot),0x00010000@0x000c