Android系统开发之启动过程（代码）

Android的启动

1.Linux内核启动

Android本质上就是一个基于Linux内核的操作系统，一个完整的Linux系统首先会将一个Linux内核装载到内存，也就是编译Linux内核源代码生成的bzImage文件，当Linux内核加载完后，要做的第一件事就是调用init程序。

2.init进程（init.c）

init是kernel启动的第一个进程，相应的代码在./system/core/init/下，可以从该目录下的init.c，init.c这个文件做了下面几件事：

1. 初始化属性

2. 处理配置文件的命令（主要是init.rc文件），包括处理各种Action。

3. 性能分析（使用bootchart工具）。

4. 无限循环执行command（作为父进程启动其他的子进程）。

2 .1  2.1初始化语言(init.rc,AIL)

分析init.rc就先要了解AIL，详见AIL.doc

 

AM335x下有：

Init.rc（入口）

init.usb.rc

Init.trace.rc

init.am335xevm.rc

init.am335xevm.usb.rc

 分析init.rc脚步前需要了解什么是AIL，http://dengzhangtao.iteye.com/blog/1984286

# Copyright (C) 2012 The Android Open Source Project
#
# IMPORTANT: Do not create world writable files or directories.
# This is a common source of Android security bugs.
#

import /init.${ro.hardware}.rc
import /init.usb.rc
import /init.trace.rc

on early-init
    # Set init and its forked children's oom_adj.进程的oom_adj值也就代表了它的优先级。oom_adj值越高代表该进程优先级越低
    write /proc/1/oom_adj -16
    #启动ueventd服务
    start ueventd

# create mountpoints
    mkdir /mnt 0775 root system

on init
#设置系统时钟基准
sysclktz 0 

loglevel 3

# setup the global environment
    export PATH /sbin:/vendor/bin:/system/sbin:/system/bin:/system/xbin
    export LD_LIBRARY_PATH /vendor/lib:/system/lib
    export ANDROID_BOOTLOGO 1
    export ANDROID_ROOT /system
    export ANDROID_ASSETS /system/app
    export ANDROID_DATA /data
    export ASEC_MOUNTPOINT /mnt/asec
    export LOOP_MOUNTPOINT /mnt/obb
    export BOOTCLASSPATH /system/framework/core.jar:/system/framework/core-junit.jar:/system/framework/bouncycastle.jar:/system/framework/ext.jar:/system/framework/framework.jar:/system/framework/android.policy.jar:/system/framework/services.jar:/system/framework/apache-xml.jar

# Backward compatibility
    symlink /system/etc /etc
    symlink /sys/kernel/debug /d

# Right now vendor lives on the same filesystem as system,
# but someday that may change.
    symlink /system/vendor /vendor

# Create cgroup mount point for cpu accounting  目录, 权限 ,所有者 ,用户组
    mkdir /acct
    mount cgroup none /acct cpuacct
    mkdir /acct/uid

    mkdir /system
    mkdir /data 0771 system system
    mkdir /cache 0770 system cache
    mkdir /config 0500 root root

    # Directory for putting things only root should see.
    mkdir /mnt/secure 0700 root root

    # Directory for staging bindmounts
    mkdir /mnt/secure/staging 0700 root root

    # Directory-target for where the secure container
    # imagefile directory will be bind-mounted
    mkdir /mnt/secure/asec  0700 root root

    # Secure container public mount points.
    mkdir /mnt/asec  0700 root system
    mount tmpfs tmpfs /mnt/asec mode=0755,gid=1000

    # Filesystem image public mount points.
    mkdir /mnt/obb 0700 root system
    mount tmpfs tmpfs /mnt/obb mode=0755,gid=1000

    write /proc/sys/kernel/panic_on_oops 1
    write /proc/sys/kernel/hung_task_timeout_secs 0
    write /proc/cpu/alignment 4
    write /proc/sys/kernel/sched_latency_ns 10000000
    write /proc/sys/kernel/sched_wakeup_granularity_ns 2000000
    write /proc/sys/kernel/sched_compat_yield 1
    write /proc/sys/kernel/sched_child_runs_first 0
    write /proc/sys/kernel/randomize_va_space 2
    write /proc/sys/kernel/kptr_restrict 2
    write /proc/sys/kernel/dmesg_restrict 1
    write /proc/sys/vm/mmap_min_addr 32768
    write /proc/sys/kernel/sched_rt_runtime_us 950000
    write /proc/sys/kernel/sched_rt_period_us 1000000

# Create cgroup mount points for process groups
    mkdir /dev/cpuctl
    mount cgroup none /dev/cpuctl cpu
    chown system system /dev/cpuctl
    chown system system /dev/cpuctl/tasks
    chmod 0660 /dev/cpuctl/tasks
    write /dev/cpuctl/cpu.shares 1024
    write /dev/cpuctl/cpu.rt_runtime_us 950000
    write /dev/cpuctl/cpu.rt_period_us 1000000

    mkdir /dev/cpuctl/apps
    chown system system /dev/cpuctl/apps/tasks
    chmod 0666 /dev/cpuctl/apps/tasks
    write /dev/cpuctl/apps/cpu.shares 1024
    write /dev/cpuctl/apps/cpu.rt_runtime_us 800000
    write /dev/cpuctl/apps/cpu.rt_period_us 1000000

    mkdir /dev/cpuctl/apps/bg_non_interactive
    chown system system /dev/cpuctl/apps/bg_non_interactive/tasks
    chmod 0666 /dev/cpuctl/apps/bg_non_interactive/tasks
    # 5.0 %
    write /dev/cpuctl/apps/bg_non_interactive/cpu.shares 52
    write /dev/cpuctl/apps/bg_non_interactive/cpu.rt_runtime_us 700000
    write /dev/cpuctl/apps/bg_non_interactive/cpu.rt_period_us 1000000

# Allow everybody to read the xt_qtaguid resource tracking misc dev.
# This is needed by any process that uses socket tagging.
    chmod 0644 /dev/xt_qtaguid

#on fs
# mount mtd partitions
    # Mount /system rw first to give the filesystem a chance to save a checkpoint
#    mount yaffs2 mtd@system /system
#    mount yaffs2 mtd@system /system ro remount
#    mount yaffs2 mtd@userdata /data nosuid nodev
#    mount yaffs2 mtd@cache /cache nosuid nodev

on post-fs
    # once everything is setup, no need to modify /
#    mount rootfs rootfs / ro remount

    # We chown/chmod /cache again so because mount is run as root + defaults
    chown system cache /cache
    chmod 0770 /cache

    # This may have been created by the recovery system with odd permissions
    chown system cache /cache/recovery
    chmod 0770 /cache/recovery

    #change permissions on vmallocinfo so we can grab it from bugreports
    chown root log /proc/vmallocinfo
    chmod 0440 /proc/vmallocinfo

    #change permissions on kmsg & sysrq-trigger so bugreports can grab kthread stacks
    chown root system /proc/kmsg
    chmod 0440 /proc/kmsg
    chown root system /proc/sysrq-trigger
    chmod 0220 /proc/sysrq-trigger

    # create the lost+found directories, so as to enforce our permissions
    mkdir /cache/lost+found 0770 root root

on post-fs-data
    # We chown/chmod /data again so because mount is run as root + defaults
    chown system system /data
    chmod 0771 /data

    # Create dump dir and collect dumps.
    # Do this before we mount cache so eventually we can use cache for
    # storing dumps on platforms which do not have a dedicated dump partition.
    mkdir /data/dontpanic 0750 root log

    # Collect apanic data, free resources and re-arm trigger
    copy /proc/apanic_console /data/dontpanic/apanic_console
    chown root log /data/dontpanic/apanic_console
    chmod 0640 /data/dontpanic/apanic_console

    copy /proc/apanic_threads /data/dontpanic/apanic_threads
    chown root log /data/dontpanic/apanic_threads
    chmod 0640 /data/dontpanic/apanic_threads

    write /proc/apanic_console 1

    # create basic filesystem structure
    mkdir /data/misc 01771 system misc
    mkdir /data/misc/bluetoothd 0770 bluetooth bluetooth
    mkdir /data/misc/bluetooth 0770 system system
    mkdir /data/misc/keystore 0700 keystore keystore
    mkdir /data/misc/keychain 0771 system system
    mkdir /data/misc/ 0770 system
    mkdir /data/misc/systemkeys 0700 system system
    # give system access to wpa_supplicant.conf for backup and restore
    mkdir /data/misc/wifi 0770 wifi wifi
    chmod 0660 /data/misc/wifi/wpa_supplicant.conf
    mkdir /data/local 0751 root root

    # For security reasons, /data/local/tmp should always be empty.
    # Do not place files or directories in /data/local/tmp
    mkdir /data/local/tmp 0771 shell shell
    mkdir /data/data 0771 system system
    mkdir /data/app-private 0771 system system
    mkdir /data/app-asec 0700 root root
    mkdir /data/app 0771 system system
    mkdir /data/property 0700 root root
    mkdir /data/ssh 0750 root shell
    mkdir /data/ssh/empty 0700 root root

    # create dalvik-cache, so as to enforce our permissions
    mkdir /data/dalvik-cache 0771 system system

    # create resource-cache and double-check the perms
    mkdir /data/resource-cache 0771 system system
    chown system system /data/resource-cache
    chmod 0771 /data/resource-cache

    # create the lost+found directories, so as to enforce our permissions
    mkdir /data/lost+found 0770 root root

    # create directory for DRM plug-ins - give drm the read/write access to
    # the following directory.
    mkdir /data/drm 0770 drm drm

    # If there is no fs-post-data action in the init..rc file, you
    # must uncomment this line, otherwise encrypted filesystems
    # won't work.
    # Set indication (checked by vold) that we have finished this action
    #setprop vold.post_fs_data_done 1

on boot
# basic network init
    ifup lo
    hostname localhost
    domainname localdomain

# set RLIMIT_NICE to allow priorities from 19 to -20
    setrlimit 13 40 40

# Memory management.  Basic kernel parameters, and allow the high
# level system server to be able to adjust the kernel OOM driver
# parameters to match how it is managing things.
    write /proc/sys/vm/overcommit_memory 1
    write /proc/sys/vm/min_free_order_shift 4
    chown root system /sys/module/lowmemorykiller/parameters/adj
    chmod 0664 /sys/module/lowmemorykiller/parameters/adj
    chown root system /sys/module/lowmemorykiller/parameters/minfree
    chmod 0664 /sys/module/lowmemorykiller/parameters/minfree

    # Tweak background writeout
    write /proc/sys/vm/dirty_expire_centisecs 200
    write /proc/sys/vm/dirty_background_ratio  5

    # Permissions for System Server and daemons.
    chown radio system /sys/android_power/state
    chown radio system /sys/android_power/request_state
    chown radio system /sys/android_power/acquire_full_wake_lock
    chown radio system /sys/android_power/acquire_partial_wake_lock
    chown radio system /sys/android_power/release_wake_lock
    chown system system /sys/power/state
    chown system system /sys/power/wakeup_count
    chown radio system /sys/power/wake_lock
    chown radio system /sys/power/wake_unlock
    chmod 0660 /sys/power/state
    chmod 0660 /sys/power/wake_lock
    chmod 0660 /sys/power/wake_unlock

    chown system system /sys/devices/system/cpu/cpufreq/interactive/timer_rate
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/timer_rate
    chown system system /sys/devices/system/cpu/cpufreq/interactive/min_sample_time
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/min_sample_time
    chown system system /sys/devices/system/cpu/cpufreq/interactive/hispeed_freq
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/hispeed_freq
    chown system system /sys/devices/system/cpu/cpufreq/interactive/go_hispeed_load
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/go_hispeed_load
    chown system system /sys/devices/system/cpu/cpufreq/interactive/above_hispeed_delay
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/above_hispeed_delay
    chown system system /sys/devices/system/cpu/cpufreq/interactive/boost
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/boost
    chown system system /sys/devices/system/cpu/cpufreq/interactive/boostpulse
    chown system system /sys/devices/system/cpu/cpufreq/interactive/input_boost
    chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/input_boost

    # Assume SMP uses shared cpufreq policy for all CPUs
    chown system system /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
    chmod 0660 /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq

    chown system system /sys/class/timed_output/vibrator/enable
    chown system system /sys/class/leds/keyboard-backlight/brightness
    chown system system /sys/class/leds/lcd-backlight/brightness
    chown system system /sys/class/leds/button-backlight/brightness
    chown system system /sys/class/leds/jogball-backlight/brightness
    chown system system /sys/class/leds/red/brightness
    chown system system /sys/class/leds/green/brightness
    chown system system /sys/class/leds/blue/brightness
    chown system system /sys/class/leds/red/device/grpfreq
    chown system system /sys/class/leds/red/device/grppwm
    chown system system /sys/class/leds/red/device/blink
    chown system system /sys/class/leds/red/brightness
    chown system system /sys/class/leds/green/brightness
    chown system system /sys/class/leds/blue/brightness
    chown system system /sys/class/leds/red/device/grpfreq
    chown system system /sys/class/leds/red/device/grppwm
    chown system system /sys/class/leds/red/device/blink
    chown system system /sys/class/timed_output/vibrator/enable
    chown system system /sys/module/sco/parameters/disable_esco
    chown system system /sys/kernel/ipv4/tcp_wmem_min
    chown system system /sys/kernel/ipv4/tcp_wmem_def
    chown system system /sys/kernel/ipv4/tcp_wmem_max
    chown system system /sys/kernel/ipv4/tcp_rmem_min
    chown system system /sys/kernel/ipv4/tcp_rmem_def
    chown system system /sys/kernel/ipv4/tcp_rmem_max
    chown root radio /proc/cmdline

# Define TCP buffer sizes for various networks
#   ReadMin, ReadInitial, ReadMax, WriteMin, WriteInitial, WriteMax,
    setprop net.tcp.buffersize.default 4096,87380,110208,4096,16384,110208
    setprop net.tcp.buffersize.wifi    524288,1048576,2097152,262144,524288,1048576
    setprop net.tcp.buffersize.lte     524288,1048576,2097152,262144,524288,1048576
    setprop net.tcp.buffersize.umts    4094,87380,110208,4096,16384,110208
    setprop net.tcp.buffersize.hspa    4094,87380,262144,4096,16384,262144
    setprop net.tcp.buffersize.edge    4093,26280,35040,4096,16384,35040
    setprop net.tcp.buffersize.gprs    4092,8760,11680,4096,8760,11680

# Set this property so surfaceflinger is not started by system_init
    setprop system_init.startsurfaceflinger 0

    class_start core
    class_start main

on nonencrypted
    class_start late_start

on charger
    class_start charger

on property:vold.decrypt=trigger_reset_main
    class_reset main

on property:vold.decrypt=trigger_load_persist_props
    load_persist_props

on property:vold.decrypt=trigger_post_fs_data
    trigger post-fs-data

on property:vold.decrypt=trigger_restart_min_framework
    class_start main

on property:vold.decrypt=trigger_restart_framework
    class_start main
    class_start late_start

on property:vold.decrypt=trigger_shutdown_framework
    class_reset late_start
    class_reset main

## Daemon processes to be run by init.
#ueventd服务会读取 /ueventd.rc 和 /ueventd.$hadrware.rc 文件，解析跟 init.rc 解析类似，
#主要是对文件系统的权限和用户进行设置：（代码：system/core/init/ueventd.c）
service ueventd /sbin/ueventd
    class core
    critical
   
#控制台中可以执行root权限的话 user shell 改为 user root
service console /system/bin/sh
    class core
    console
    disabled
#    user shell 
    group log

on property:ro.debuggable=1
    start console

# adbd is controlled via property triggers in init..usb.rc
# adb 命令
service adbd /sbin/adbd
    class core
    disabled

# adbd on at boot in emulator
on property:ro.kernel.qemu=1
    start adbd
   
#服务管理 是应用程序与服务沟通的桥梁。
service servicemanager /system/bin/servicemanager
    class core
    user system
    group system
    critical
    #onrestart 当服务重启，执行一个命令
    onrestart restart zygote
    onrestart restart media
    onrestart restart surfaceflinger
    onrestart restart drm
   
#当有这外存储设备插入时，就需要监视这种变化，并加载相应的驱动程序，然后报告给系统和应用程序有新存储设备可以使用。
# /system/vold/main.cpp
service vold /system/bin/vold
    class core
    socket vold stream 0660 root mount
    ioprio be 2
   
#netd功能：
#    (1)Linux Kernel 用于检测 network 相关的所有 event 事件。
#    (2)Netd 作为 Kernel 与 Framework 之间通信的桥梁。
#   (3)Framework 层操作 Netd,向 Netd 发送操作命令。
#   (4)UI 与 Framework 交互,用于用户进行网络的操控。
service netd /system/bin/netd
    class main
    socket netd stream 0660 root system
    socket dnsproxyd stream 0660 root inet
    socket mdns stream 0660 root system
   
#debug服务，Log的使用
service debuggerd /system/bin/debuggerd
    class main

# modify by dengzt 2013,8,28
#电话服务
#service ril-daemon /system/bin/rild
#    class main
#    socket rild stream 660 root radio
#    socket rild-debug stream 660 radio system
#    user root
#    group radio cache inet misc audio sdcard_r sdcard_rw log

#管理设备的帧缓冲区
service surfaceflinger /system/bin/surfaceflinger
    class main
    user system
    group graphics
    onrestart restart zygote

#根据用户的命令创建应用程序
service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
    class main
    socket zygote stream 660 root system
    onrestart write /sys/android_power/request_state wake
    onrestart write /sys/power/state on
    onrestart restart media
    onrestart restart netd
   
#DRM，英文全称为Digital Rights Management，译为数字版权管理
service drm /system/bin/drmserver
    class main
    user drm
    group drm system inet drmrpc sdcard_r
   
#多媒体服务，照相，音频
service media /system/bin/mediaserver
    class main
    user media
    group audio camera inet net_bt net_bt_admin net_bw_acct drmrpc
    ioprio rt 4
   
#开机动画服务
service bootanim /system/bin/bootanimation
    class main
    user graphics
    group graphics
    disabled
    oneshot

#跨进程的数据交互是通过dbus来的，这里默认是蓝牙才能访问
service dbus /system/bin/dbus-daemon --system --nofork
    class main
    socket dbus stream 660 bluetooth bluetooth
    user bluetooth
    group bluetooth net_bt_admin

#service bluetoothd /system/bin/bluetoothd -n
#    class main
#    socket bluetooth stream 660 bluetooth bluetooth
#    socket dbus_bluetooth stream 660 bluetooth bluetooth
    # init.rc does not yet support applying capabilities, so run as root and
    # let bluetoothd drop uid to bluetooth with the right linux capabilities
#    group bluetooth net_bt_admin misc
#    disabled

#apk安装服务，源码frameworks/base/cmds/installd/
service installd /system/bin/installd
    class main
    socket installd stream 600 system system

service flash_recovery /system/etc/install-recovery.sh
    class main
    oneshot
   
#VPN服务
service racoon /system/bin/racoon
    class main
    socket racoon stream 600 system system
    # IKE uses UDP port 500. Racoon will setuid to after binding the port.
    group net_admin inet
    disabled
    oneshot
   
#Media Transfer Protocol多媒体传输协议服务
service mtpd /system/bin/mtpd
    class main
    socket mtpd stream 600 system system
    user
    group net_admin inet net_raw
    disabled
    oneshot
   
#应用签名服务
service keystore /system/bin/keystore /data/misc/keystore
    class main
    user keystore
    group keystore drmrpc
    socket keystore stream 666
   
#性能测试工具
service dumpstate /system/bin/dumpstate -s
    class main
    socket dumpstate stream 0660 shell log
    disabled
    oneshot
   
#SSH为一项创建在应用层和传输层基础上的安全协议，为计算机上的Shell（壳层）提供安全的传输和使用环境。
service sshd /system/bin/start-ssh
    class main
    disabled
   
#Bonjour技术在android平台上的定制为mdnsd 使用Bonjour的设备在网络中自动组播它们自己的服务信息并监听其它设备的服务信息。设备之间就像在打招呼
service mdnsd /system/bin/mdnsd
    class main
    user mdnsr
    group inet net_raw
    socket mdnsd stream 0660 mdnsr inet
    disabled
    oneshot