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。

1. Android架构介绍
2. Android启动概述
3. BootLoader介绍
4. Kernel初始化介绍
5. Init初始化介绍
6. Zygote启动介绍
7. SystemServer启动介绍
8. Launcher启动介绍
9. 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：

1. Android启动流程简析（一）
2. Android启动流程简析（二）
3. 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：

1. 调用thread_init_early初始化线程系统
2. 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
3. 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
4. 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
5. 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
6. 在thread_init函数中初始化定时器
7. 调用timer_init初始化内核定时器
8. 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：

1. arch_init主要是打印一些信息
2. 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
3. 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：

1. 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
2. 取得设备的device_info信息，保存到device变量中
3. 初始化lcd驱动，显示手机开机后的第一副图片
4. 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
5. 检查按键判断是进入recovery还是fastboot
6. 检查重启模式
7. 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 <linux/linkage.h>

#include <asm/page.h>

    .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<ServiceParser>(&sm));
parser.AddSectionParser("on", std::make_unique<ActionParser>(&am));
parser.AddSectionParser("import", std::make_unique<ImportParser>(&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<std::size_t>::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：

1. 启动Hidl服务，主要是DisplayService
2. 启动线程池
3. 初始化SurfaceFlinger
4. 将SurfaceFlinger和GpuService注册到ServiceManager
5. 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<ProcessState> ps(ProcessState::self());
    ps->startThreadPool();

    // instantiate surfaceflinger
    sp<SurfaceFlinger> 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<IServiceManager> sm(defaultServiceManager());
    sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false);

    // publish GpuService
    sp<GpuService> 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, &param) != 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）