最近一时兴起，想对Android的启动流程进行一次分析，经过一番整理，从以下几个方面进行总结，代码部分只讨论思路，不论细节。
- Android架构介绍
- Android启动概述
- BootLoader介绍
- Kernel初始化介绍
- Init初始化介绍
- Zygote启动介绍
- SystemServer启动介绍
- Launcher启动介绍
- Log抓取与分析方法
由于发表文章的时候提示内容过长无法发布，于是把文章拆成了三部分发布：
- Android启动流程简析（一）
- Android启动流程简析（二）
- Android启动流程简析（三）
1. Android架构介绍
Android的架构可以从架构图得知，主要分四层：
Android经典的四层架构图
Android架构图
每一层的作用不做介绍，这里主要讲涉及的镜像有boot.img、system.img、vendor.img、recovery.img、userdata.img、cache.img，与平台相关的镜像有lk.bin（MTK）、preloader.img（MTK）、logo.bin（MTK）、emmc_appsboot.mbn（QCOM）、splash.img（QCOM）等，通常来说，修改kernel层通常编译boot.img即可，修改Framework层或Native层主要是编译system.img，在Android O之后修改某些模块还需要编译vendor.img，主要是受Android O Treble的影响，具体问题需要具体分析。
2. Android启动概述
概述：Loader > Kernel > Native > Framework > Application
细分：BootRom > Bootloader > Kernel > Init > Zygote > SystemServer > Launcher
- Loader层主要包括Boot Rom和Boot Loader
- Kernel层主要是Android内核层
- Native层主要是包括init进程以及其fork出来的用户空间的守护进程、HAL层、开机动画等
- Framework层主要是AMS和PMS等Service的初始化
- Application层主要指SystemUI、Launcher的启动
3. BootLoader介绍
Bootloader 就是在操作系统内核运行之前运行的一段小程序。通过这段小程序，我们可以初始化硬件设备、建立内存空间的映射图，从而将系统的软硬件环境带到一个合适的状态，以便为最终调用操作系统内核准备好正确的环境。
调用流程：
crt0.S > kmain > arch_init > target_init > apps_init > aboot_init
3.1 crt0.S
- 高通平台：alps/bootable/bootloader/lk/arch/{paltform}/crt0.S
- MTK平台：alps/vendor/mediatek/proprietary/bootable/bootloader/lk/arch/{paltform}/crt0.S
platform主要有arm、arm64、x86、x86-64等，crt0.S代码大体如下，在_start中先主要完成CPU初始化，禁用mmu，禁用cache，初始化异常向量表等操作，最后将直接跳转到函数kmain中
.section ".text.boot"
.globl _start
_start:
b reset
b arm_undefined
b arm_syscall
b arm_prefetch_abort
b arm_data_abort
b arm_reserved
b arm_irq
b arm_fiq
/*pre-loader to uboot argument Location*/
.global BOOT_ARGUMENT_LOCATION
BOOT_ARGUMENT_LOCATION:
.word 0x00000000
...
#if (!ENABLE_NANDWRITE)
#if WITH_CPU_WARM_BOOT
ldr r0, warm_boot_tag
cmp r0, #1
/* if set, warm boot */
ldreq pc, =BASE_ADDR
mov r0, #1
str r0, warm_boot_tag
#endif
#endif
...
#if defined(ARM_CPU_CORTEX_A8) || defined(ARM_CPU_CORTEX_A9)
DSB
ISB
#endif
bl kmain
b .
3.2 kmain
- 高通平台：alps/bootable/bootloader/lk/kernel/main.c
- MTK平台：alps/vendor/mediatek/proprietary/bootable/bootloader/lk/kernel/main.c
/* called from crt0.S */
void kmain(void) __NO_RETURN __EXTERNALLY_VISIBLE;
void kmain(void)
{
#if !defined(MACH_FPGA) && !defined(SB_LK_BRINGUP)
boot_time = get_timer(0);
#endif
// get us into some sort of thread context
thread_init_early();
// early arch stuff
arch_early_init();
// do any super early platform initialization
platform_early_init();
#if defined(MACH_FPGA) || defined(SB_LK_BRINGUP)
boot_time = get_timer(0);
#endif
// do any super early target initialization
target_early_init();
dprintf(INFO, "welcome to lk\n\n");
// deal with any static constructors
dprintf(SPEW, "calling constructors\n");
call_constructors();
// bring up the kernel heap
dprintf(SPEW, "initializing heap\n");
heap_init();
// initialize the threading system
dprintf(SPEW, "initializing threads\n");
thread_init();
// initialize the dpc system
dprintf(SPEW, "initializing dpc\n");
dpc_init();
// initialize kernel timers
dprintf(SPEW, "initializing timers\n");
timer_init();
#ifdef MTK_LK_IRRX_SUPPORT
mtk_ir_init(0);
#endif
#if (!ENABLE_NANDWRITE)
// create a thread to complete system initialization
dprintf(SPEW, "creating bootstrap completion thread\n");
thread_t *thread_bs2 = thread_create("bootstrap2", &bootstrap2, NULL,
DEFAULT_PRIORITY, DEFAULT_STACK_SIZE);
if (thread_bs2)
thread_resume(thread_bs2);
else {
dprintf(CRITICAL, "Error: Cannot create bootstrap2 thread!\n");
assert(0);
}
thread_t *thread_io = thread_create("iothread", &iothread, NULL,
IO_THREAD_PRIORITY, DEFAULT_STACK_SIZE);
if (thread_io)
thread_resume(thread_io);
else {
dprintf(CRITICAL, "Error: Cannot create I/O thread!\n");
assert(0);
}
// enable interrupts
exit_critical_section();
// become the idle thread
thread_become_idle();
#else
bootstrap_nandwrite();
#endif
}
kmain主要流程：
- 调用thread_init_early初始化线程系统
- 调用arch_early_init中判断如果存在mmu就初始化，设置异常向量基地址，使能中断相关寄存器
- 在platform_early_init中完成初始化硬件时钟、手机的主板等操作，这个函数每种cpu的实现都不一样，定义在bootable\bootloader\lk\platform{cpu型号}\platform.c下
- target_early_init中完成初始化uart端口的操作，这个函数的实现在bootable\bootloader\lk\target{cpu型号}\init.c
- 调用函数heap_init完成内核堆栈的初始化，用与kmalloc等函数的内存分配
- 在thread_init函数中初始化定时器
- 调用timer_init初始化内核定时器
- 如果没有定义ENABLE_NANDWRITE，就创建出一个名为bootstrap2的线程，然后运行这个线程。退出临界区，开中断；如果定义了ENABLE_NANDWRITE，在timer_init之后将执行bootstrap_nandwrite
3.3 bootstrap2
static int bootstrap2(void *arg)
{
dprintf(SPEW, "top of bootstrap2()\n");
print_stack_of_current_thread();
arch_init();
// XXX put this somewhere else
#if WITH_LIB_BIO
bio_init();
#endif
#if WITH_LIB_FS
fs_init();
#endif
// initialize the rest of the platform
dprintf(SPEW, "initializing platform\n");
platform_init();
// initialize the target
dprintf(SPEW, "initializing target\n");
target_init();
dprintf(SPEW, "calling apps_init()\n");
apps_init();
return 0;
}
kmain bootstrap2阶段：
- arch_init主要是打印一些信息
- target_init主要完成的操作有
- 从共享内存中读写xbl提供的pmic信息
- 初始化spmi总线，用于cpu和pmic通信
- 初始化ap与rpm通信通道
- 初始化按键
- 判断内核是否签名，当使用的是签名的内核时，需要初始化加密解密引擎
- 判断是从usf还是emmc启动
- 获取分区表信息
- 判断电池电压是否过低，过低则进入预充电
- 和tz通信
- 初始化emmc或ufs中的rpmb用户加解密认证分区
- 运行keymaster
- apps_init主要完成一些应用功能的初始化，并调用aboot_init
3.4 aboot_init
aboot_init在aboot.c中，主要完成以下操作：
- 根据target_is_emmc_boot()判断是否是从emmc存储设备上启动，然后分别获取对应存储设备的页大小和页掩码
- 取得设备的device_info信息，保存到device变量中
- 初始化lcd驱动，显示手机开机后的第一副图片
- 获取emmc或者flash芯片的产品序列号，最后在启动kernel时通过cmdline中的androidboot.serialno参数传给内核
- 检查按键判断是进入recovery还是fastboot
- 检查重启模式
- 跳转到kernel
4. Kernel初始化介绍
Kernel初始化可以分成三部分：zImage解压缩、kernel的汇编启动阶段、Kernel的C启动阶段
内核启动引导地址由bootp.lds决定，内核启动的执行的第一条的代码在head.S文件中，主要功能是实现压缩内核的解压和跳转到内核vmlinux内核的入口
4.1 head.S
/*
* Non-board-specific low-level startup code
*
* Copyright (C) 2004-2006 Atmel Corporation
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include
#include
.section .init.text,"ax"
.global kernel_entry
kernel_entry:
/* Start the show */
lddpc pc, kernel_start_addr
.align 2
kernel_start_addr:
.long start_kernel
kernel的C启动阶段可以理解为真正的启动阶段，从head.S看到，最终调用的是kernel/init/main.c的start_kernel()函数
4.2 start_kernel
asmlinkage __visible void __init start_kernel(void)
{
char *command_line;
char *after_dashes;
/*
* Need to run as early as possible, to initialize the lockdep hash:
*/
lockdep_init();
set_task_stack_end_magic(&init_task);
smp_setup_processor_id();
debug_objects_early_init();
/*
* Set up the the initial canary ASAP:
*/
boot_init_stack_canary();
cgroup_init_early();
local_irq_disable();
early_boot_irqs_disabled = true;
/*
* Interrupts are still disabled. Do necessary setups, then
* enable them
*/
boot_cpu_init();
page_address_init();
pr_notice("%s", linux_banner);
setup_arch(&command_line);
mm_init_cpumask(&init_mm);
setup_command_line(command_line);
setup_nr_cpu_ids();
setup_per_cpu_areas();
smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
build_all_zonelists(NULL, NULL);
page_alloc_init();
pr_notice("Kernel command line: %s\n", boot_command_line);
parse_early_param();
after_dashes = parse_args("Booting kernel",
static_command_line, __start___param,
__stop___param - __start___param,
-1, -1, NULL, &unknown_bootoption);
if (!IS_ERR_OR_NULL(after_dashes))
parse_args("Setting init args", after_dashes, NULL, 0, -1, -1, NULL, set_init_arg);
jump_label_init();
/*
* These use large bootmem allocations and must precede kmem_cache_init()
*/
setup_log_buf(0);
pidhash_init();
vfs_caches_init_early();
sort_main_extable();
trap_init();
mm_init();
/*
* Set up the scheduler prior starting any interrupts (such as the
* timer interrupt). Full topology setup happens at smp_init()
* time - but meanwhile we still have a functioning scheduler.
*/
sched_init();
/*
* Disable preemption - early bootup scheduling is extremely
* fragile until we cpu_idle() for the first time.
*/
preempt_disable();
if (WARN(!irqs_disabled(), "Interrupts were enabled *very* early, fixing it\n"))
local_irq_disable();
idr_init_cache();
rcu_init();
/* trace_printk() and trace points may be used after this */
trace_init();
context_tracking_init();
radix_tree_init();
/* init some links before init_ISA_irqs() */
early_irq_init();
init_IRQ();
tick_init();
rcu_init_nohz();
init_timers();
hrtimers_init();
softirq_init();
timekeeping_init();
time_init();
sched_clock_postinit();
perf_event_init();
profile_init();
call_function_init();
WARN(!irqs_disabled(), "Interrupts were enabled early\n");
early_boot_irqs_disabled = false;
local_irq_enable();
kmem_cache_init_late();
/*
* HACK ALERT! This is early. We're enabling the console before
* we've done PCI setups etc, and console_init() must be aware of
* this. But we do want output early, in case something goes wrong.
*/
console_init();
if (panic_later)
panic("Too many boot %s vars at `%s'", panic_later, panic_param);
lockdep_info();
/*
* Need to run this when irqs are enabled, because it wants
* to self-test [hard/soft]-irqs on/off lock inversion bugs
* too:
*/
locking_selftest();
#ifdef CONFIG_BLK_DEV_INITRD
if (initrd_start && !initrd_below_start_ok &&
page_to_pfn(virt_to_page((void *)initrd_start)) < min_low_pfn) {
pr_crit("initrd overwritten (0x%08lx < 0x%08lx) - disabling it.\n",
page_to_pfn(virt_to_page((void *)initrd_start)), min_low_pfn);
initrd_start = 0;
}
#endif
page_ext_init();
debug_objects_mem_init();
kmemleak_init();
setup_per_cpu_pageset();
numa_policy_init();
if (late_time_init)
late_time_init();
sched_clock_init();
calibrate_delay();
pidmap_init();
anon_vma_init();
acpi_early_init();
#ifdef CONFIG_X86
if (efi_enabled(EFI_RUNTIME_SERVICES))
efi_enter_virtual_mode();
#endif
#ifdef CONFIG_X86_ESPFIX64
/* Should be run before the first non-init thread is created */
init_espfix_bsp();
#endif
thread_stack_cache_init();
cred_init();
fork_init();
proc_caches_init();
buffer_init();
key_init();
security_init();
dbg_late_init();
vfs_caches_init();
signals_init();
/* rootfs populating might need page-writeback */
page_writeback_init();
proc_root_init();
nsfs_init();
cpuset_init();
cgroup_init();
taskstats_init_early();
delayacct_init();
check_bugs();
acpi_subsystem_init();
sfi_init_late();
if (efi_enabled(EFI_RUNTIME_SERVICES)) {
efi_late_init();
efi_free_boot_services();
}
ftrace_init();
/* Do the rest non-__init'ed, we're now alive */
rest_init();
}
start_kernel()函数中执行了大量的初始化操作：
- setup_arch()：主要做一些板级初始化，cpu初始化，tag参数解析，u-boot传递的cmdline解析，建立mmu工作页表，初始化内存布局，调用mmap_io建立GPIO、IRQ、MEMCTRL、UART，及其他外设的静态映射表，对时钟，定时器，uart进行初始化
- sched_init()：初始化每个处理器的可运行队列，设置系统初始化进程即0号进程
- softirq_init()：内核的软中断机制初始化函数
- console_init()：初始化系统的控制台结构
- rest_init()：调用kernel_thread()创建1号内核线程，调用schedule()函数切换当前进程，在调用该函数之前，Linux系统中只有两个进程，即0号进程init_task和1号进程kernel_init，其中kernel_init进程也是刚刚被创建的。调用该函数后，1号进程kernel_init将会运行
4.3 kernel进程
Linux下有3个特殊的进程，idle（swapper）进程（PID = 0）、init进程（PID = 1）和kthreadd（PID = 2）
- idle（swapper）进程由系统自动创建，运行在内核态
idle进程其pid=0，其前身是系统创建的第一个进程，也是唯一一个没有通过fork或者kernel_thread产生的进程。
完成加载系统后，演变为进程调度、交换，常常被称为交换进程。 - init进程由idle通过kernel_thread创建，在内核空间完成初始化后，加载init程序，并最终转变为用户空间的init进程
由0进程创建，完成系统的初始化. 是系统中所有其它用户进程的祖先进程。
Linux中的所有进程都是有init进程创建并运行的。首先Linux内核启动，然后在用户空间中启动init进程，再启动其他系统进程。
在系统启动完成后，init将变为守护进程监视系统其他进程。 - kthreadd进程由idle通过kernel_thread创建，并始终运行在内核空间，负责所有内核线程的调度和管理
它的任务就是管理和调度其他内核线程kernel_thread，会循环执行一个kthreadd的函数，该函数的作用就是运行kthread_create_list全局链表中维护的kthread，当我们调用kernel_thread创建的内核线程会被加入到此链表中，因此所有的内核线程都是直接或者间接的以kthreadd为父进程。
5. Init初始化介绍
init进程是Linux内核启动后创建的第一个用户空间的进程，init在初始化过程中会启动很多重要的守护进程。
5.1 init启动
代码位于alps/system/core/init/init.cpp
init.cpp的mian函数入口同时也是ueventd和watchdogd守护进程的入口，通过参数进行控制
int main(int argc, char** argv) {
if (!strcmp(basename(argv[0]), "ueventd")) {
return ueventd_main(argc, argv);
}
if (!strcmp(basename(argv[0]), "watchdogd")) {
return watchdogd_main(argc, argv);
}
...
}
默认情况下，一个进程创建出来的文件和文件夹属性都是022，使用umask()函数能设置文件属性的掩码。参数为0意味着进程创建的文件属性是0777。接着创建一些基本的目录包括dev、proc、sys等，同时把分区mount到对应的目录
// Clear the umask.
umask(0);
// 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.
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));
// Don't expose the raw commandline to unprivileged processes.
chmod("/proc/cmdline", 0440);
gid_t groups[] = { AID_READPROC };
setgroups(arraysize(groups), groups);
mount("sysfs", "/sys", "sysfs", 0, NULL);
mount("selinuxfs", "/sys/fs/selinux", "selinuxfs", 0, NULL);
mknod("/dev/kmsg", S_IFCHR | 0600, makedev(1, 11));
mknod("/dev/random", S_IFCHR | 0666, makedev(1, 8));
mknod("/dev/urandom", S_IFCHR | 0666, makedev(1, 9));
init进程会调用property_init创建一个共享区域来存储属性值，初始化完后获取kernel传过来的cmdline去设置一些属性，然后初始化SELinux和安全上下文。接着会通过property_load_boot_defaults去加载default.prop等文件初始化系统属性
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.
process_kernel_dt();
process_kernel_cmdline();
// Propagate the kernel variables to internal variables
// used by init as well as the current required properties.
export_kernel_boot_props();
// Make the time that init started available for bootstat to log.
property_set("ro.boottime.init", getenv("INIT_STARTED_AT"));
property_set("ro.boottime.init.selinux", getenv("INIT_SELINUX_TOOK"));
// Set libavb version for Framework-only OTA match in Treble build.
const char* avb_version = getenv("INIT_AVB_VERSION");
if (avb_version) property_set("ro.boot.avb_version", avb_version);
// Clean up our environment.
unsetenv("INIT_SECOND_STAGE");
unsetenv("INIT_STARTED_AT");
unsetenv("INIT_SELINUX_TOOK");
unsetenv("INIT_AVB_VERSION");
// Now set up SELinux for second stage.
selinux_initialize(false);
selinux_restore_context();
property_load_boot_defaults();
export_oem_lock_status();
start_property_service();
set_usb_controller();
初始化属性和SELinux后，接着解析init.rc的文件内容，通过init.rc相关语法配置和启动进程以及启动的顺序
const BuiltinFunctionMap function_map;
Action::set_function_map(&function_map);
ActionManager& am = ActionManager::GetInstance();
ServiceManager& sm = ServiceManager::GetInstance();
Parser& parser = Parser::GetInstance();
parser.AddSectionParser("service", std::make_unique(&sm));
parser.AddSectionParser("on", std::make_unique(&am));
parser.AddSectionParser("import", std::make_unique(&parser));
std::string bootscript = GetProperty("ro.boot.init_rc", "");
if (bootscript.empty()) {
parser.ParseConfig("/init.rc");
parser.set_is_system_etc_init_loaded(
parser.ParseConfig("/system/etc/init"));
parser.set_is_vendor_etc_init_loaded(
parser.ParseConfig("/vendor/etc/init"));
parser.set_is_odm_etc_init_loaded(parser.ParseConfig("/odm/etc/init"));
} else {
parser.ParseConfig(bootscript);
parser.set_is_system_etc_init_loaded(true);
parser.set_is_vendor_etc_init_loaded(true);
parser.set_is_odm_etc_init_loaded(true);
}
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(set_kptr_restrict_action, "set_kptr_restrict");
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 = GetProperty("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");
main函数最后会进入一个死循环，每次循环都会去调用ExecuteOneCommand执行命令列表中的一条命令，如果服务挂了还会调用restart_processes重启服务
while (true) {
// By default, sleep until something happens.
int epoll_timeout_ms = -1;
if (do_shutdown && !shutting_down) {
do_shutdown = false;
if (HandlePowerctlMessage(shutdown_command)) {
shutting_down = true;
}
}
if (!(waiting_for_prop || sm.IsWaitingForExec())) {
am.ExecuteOneCommand();
}
if (!(waiting_for_prop || sm.IsWaitingForExec())) {
if (!shutting_down) restart_processes();
// If there's a process that needs restarting, wake up in time for that.
if (process_needs_restart_at != 0) {
epoll_timeout_ms = (process_needs_restart_at - time(nullptr)) * 1000;
if (epoll_timeout_ms < 0) epoll_timeout_ms = 0;
}
// If there's more work to do, wake up again immediately.
if (am.HasMoreCommands()) epoll_timeout_ms = 0;
}
epoll_event ev;
int nr = TEMP_FAILURE_RETRY(epoll_wait(epoll_fd, &ev, 1, epoll_timeout_ms));
if (nr == -1) {
PLOG(ERROR) << "epoll_wait failed";
} else if (nr == 1) {
((void (*)()) ev.data.ptr)();
}
}
init进程初始化系统后，会化身为守护进程来处理子进程的死亡信号、修改属性的请求和组合键事件
5.2 init.rc
init.rc文件位于：alps/system/core/rootdir/init.rc
在init.cpp中，启动init.rc各个阶段的顺序是early_init > init > late_init，在late_init中又会去触发其他阶段的启动，所以各个阶段在init中启动的顺序如下：
early_init > init > late_init > early-fs > fs > post-fs > late_fs > post-fs-data > zygote-start > early-boot > boot
on late-init
trigger early-fs
trigger fs
trigger post-fs
trigger late-fs
trigger post-fs-data
trigger zygote-start
trigger load_persist_props_action
trigger firmware_mounts_complete
trigger early-boot
trigger boot
在boot阶段会启动class为hal和core的服务
on boot
...
class_start hal
class_start core
init.rc中支持的命令实现在builtins.cpp中，具体语法使用可以参考alps/system/core/init/README.md
const BuiltinFunctionMap::Map& BuiltinFunctionMap::map() const {
constexpr std::size_t kMax = std::numeric_limits::max();
// clang-format off
static const Map builtin_functions = {
{"bootchart", {1, 1, do_bootchart}},
{"chmod", {2, 2, do_chmod}},
{"chown", {2, 3, do_chown}},
{"class_reset", {1, 1, do_class_reset}},
{"class_restart", {1, 1, do_class_restart}},
{"class_start", {1, 1, do_class_start}},
{"class_stop", {1, 1, do_class_stop}},
{"copy", {2, 2, do_copy}},
{"domainname", {1, 1, do_domainname}},
{"enable", {1, 1, do_enable}},
{"exec", {1, kMax, do_exec}},
{"exec_start", {1, 1, do_exec_start}},
{"export", {2, 2, do_export}},
{"hostname", {1, 1, do_hostname}},
{"ifup", {1, 1, do_ifup}},
{"init_user0", {0, 0, do_init_user0}},
{"insmod", {1, kMax, do_insmod}},
{"installkey", {1, 1, do_installkey}},
{"load_persist_props", {0, 0, do_load_persist_props}},
{"load_system_props", {0, 0, do_load_system_props}},
{"loglevel", {1, 1, do_loglevel}},
{"mkdir", {1, 4, do_mkdir}},
{"mount_all", {1, kMax, do_mount_all}},
{"mount", {3, kMax, do_mount}},
{"umount", {1, 1, do_umount}},
{"restart", {1, 1, do_restart}},
{"restorecon", {1, kMax, do_restorecon}},
{"restorecon_recursive", {1, kMax, do_restorecon_recursive}},
{"rm", {1, 1, do_rm}},
{"rmdir", {1, 1, do_rmdir}},
{"setprop", {2, 2, do_setprop}},
{"setrlimit", {3, 3, do_setrlimit}},
{"start", {1, 1, do_start}},
{"stop", {1, 1, do_stop}},
{"swapon_all", {1, 1, do_swapon_all}},
{"symlink", {2, 2, do_symlink}},
{"sysclktz", {1, 1, do_sysclktz}},
{"trigger", {1, 1, do_trigger}},
{"verity_load_state", {0, 0, do_verity_load_state}},
{"verity_update_state", {0, 0, do_verity_update_state}},
{"wait", {1, 2, do_wait}},
{"wait_for_prop", {2, 2, do_wait_for_prop}},
{"write", {2, 2, do_write}},
{"set_meizu_props", {0, 0, do_set_meizu_props}},
};
// clang-format on
return builtin_functions;
}
5.3 bootanim启动
bootanim.rc定义了bootanim属于core服务，但是设置了disable说明bootanim不是自启动的服务，需要别的服务进行唤醒。
service bootanim /system/bin/bootanimation
class core animation
user graphics
group graphics audio
disabled
oneshot
writepid /dev/stune/top-app/tasks
5.4 surfaceflinger启动
代码里搜索bootanim，可以看到是surfaceflinger服务将bootanim启动，surfaceflinger属于core服务，自启动服务，在init进程的on boot阶段会启动surfaceflinger，surfaceflinger最后会启动StartPropertySetThread从而启动bootanim
service surfaceflinger /system/bin/surfaceflinger
class core animation
user system
group graphics drmrpc readproc
onrestart restart zygote
writepid /dev/stune/foreground/tasks
socket pdx/system/vr/display/client stream 0666 system graphics u:object_r:pdx_display_client_endpoint_socket:s0
socket pdx/system/vr/display/manager stream 0666 system graphics u:object_r:pdx_display_manager_endpoint_socket:s0
socket pdx/system/vr/display/vsync stream 0666 system graphics u:object_r:pdx_display_vsync_endpoint_socket:s0
bool StartPropertySetThread::threadLoop() {
// Set property service.sf.present_timestamp, consumer need check its readiness
property_set(kTimestampProperty, mTimestampPropertyValue ? "1" : "0");
// Clear BootAnimation exit flag
property_set("service.bootanim.exit", "0");
// Start BootAnimation if not started
property_set("ctl.start", "bootanim");
// Exit immediately
return false;
}
surfaceflinger服务的main函数入口在main_surfaceflinger，主要操作有：
- 启动Hidl服务，主要是DisplayService
- 启动线程池
- 初始化SurfaceFlinger
- 将SurfaceFlinger和GpuService注册到ServiceManager
- 启动SurfaceFlinger线程
int main(int, char**) {
startHidlServices();
signal(SIGPIPE, SIG_IGN);
// When SF is launched in its own process, limit the number of
// binder threads to 4.
ProcessState::self()->setThreadPoolMaxThreadCount(4);
// start the thread pool
sp ps(ProcessState::self());
ps->startThreadPool();
// instantiate surfaceflinger
sp flinger = new SurfaceFlinger();
setpriority(PRIO_PROCESS, 0, PRIORITY_URGENT_DISPLAY);
set_sched_policy(0, SP_FOREGROUND);
// Put most SurfaceFlinger threads in the system-background cpuset
// Keeps us from unnecessarily using big cores
// Do this after the binder thread pool init
if (cpusets_enabled()) set_cpuset_policy(0, SP_SYSTEM);
// initialize before clients can connect
flinger->init();
// publish surface flinger
sp sm(defaultServiceManager());
sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false);
// publish GpuService
sp gpuservice = new GpuService();
sm->addService(String16(GpuService::SERVICE_NAME), gpuservice, false);
struct sched_param param = {0};
param.sched_priority = 2;
if (sched_setscheduler(0, SCHED_FIFO, ¶m) != 0) {
ALOGE("Couldn't set SCHED_FIFO");
}
// run surface flinger in this thread
flinger->run();
return 0;
}
surfaceflinger继承了Thread，执行run方法后，本质上是调用c++中的pthread类，线程入口函数是threadLoop，threadLoop的含义是通过一个循环不断的调用该函数，当threadLoop返回false的时候退出循环
由于bootanim的threadLoop返回false，所以启动函数在开机过程中只会执行一次
接下来的分析请看Android启动流程简析（二）