Android内核的简单分析

Android内核的简单分析

[align=center]NeilWong (neilwong@hotmail.com)[/align]
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[align=left] Google的Android操作系统已经成功面市,因为Android操作系统是基于Linux-2.6.25内核的,并且目前所有的源代码也都全部开放,因此可以简单地加以分析以方便以后向其他平台的移植工作.[/align]
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[align=left] 首先需要了解的就是Android的一些基本情况,并下载Android的源代码以方便分析.[/align]
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[align=left] Android的官方站点:[/align]
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[align=left] http://www.android.com/[/align]
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[align=left] Android Source 的官方安装方法:[/align]
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[align=left] http://source.android.com/download[/align]
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[align=left] Android的中文站点:[/align]
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[align=left] http://www.androidin.com/ [/align]
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源代码包的相应联结地址:

http://www.androidin.com/bbs/viewthread.php?tid=2337

[align=left] 我们可以采用Android官方站点推荐方式来下载Android的源代码,也可以从Android中文站点直接下载源代码程序包,随后再更新和同步.[/align]
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[align=left] 当采用Android官方推荐方式下载或者需要更新你的源代码时,都需要git工具支持, 当你的系统没有安装git或者git版本过低时,建议从下面的地址更新到最新的git包.(Android要求git版本必须大于1.5.4)[/align]

http://git.or.cz/

给git自动升级的方式:

git clone git://git.kernel.org/pub/scm/git/git.git

如果采用下载源代码包的方式,下载并展开后,在 .repo/repo 目录下有同步执行的文件repo, 你可以将其拷贝到你的PATH所在路径以备使用,例如/usr/bin等等. 或者也可以从Android站点得到最新的repo文件并复制到PATH所在路径.

wget http://android.git.kernel.org/repo

源代码包解开后,其主目录下存在repo_sync.sh文件, 其主要是执行repo sync以实现和Android站点同步代码包的目的, 当执行出错后将再一次运行repo sync命令直到同步正常结束,但原文件包含错误,建议改成下面的程序:(原文件中少了一个空格)

#!/bin/bash

echo "============start repo sync================="

repo sync

while [ $? = 1 ]; do

echo "============sync failed, re-sync again ====="

sleep 3

repo sync

done

这样, 运行sh repo_sync.sh就可以自动实现本地代码包的同步和更新动作了.

我在Fedora Core 6上经过同步之后, du -h ./mydroid, 占用空间大约是2.1G

以下为Android官方公布的架构图：



在kernel子目录下存放的就是Android的Linux Kernel了, 通过和标准的Linux 2.6.25 Kernel的对比,我们可以发现,其主要增加了以下的内容:

1. 基于ARM架构增加Gold-Fish平台,相应增加的目录如下:

kernel/arch/arm/mach-goldfish

kernel/include/asm-arm/arch-goldfish

目前Google的基于Gold-Fish的手机为G1手机，明年G2手机将面世。

该手机采用QualComm公司的高性能处理芯片MSM7201A，该芯片以ARM 11作为Application应用处理器，以ARM926T作为BaseBand主处理器(主要承载GSM／GPRS／EDGE／3G等协议栈处理)，支持JAVA硬加速(ARM本身也自带JAVA硬件处理)，包含GPS Processor, 支持2D/3D图形加速(每秒可处理4百万个多边形),另外还支持最大800万像素的Sensor, 支持MPEG 4/H.263/H.264/Real Media等多种Codec。

其中ARM926T采用的主频为274M HZ, ARM11的主频为528MHZ. (MSM7200的ARM11的主频为400M HZ)

因为没有找到MSM7201A的详细DataSheet, 因此可以简单地参考MSM7200的规格:

MSM7200_DataSheet.pdf

下面为MSM7200架构图:



2. 增加了yaffs2 FLASH文件系统,相应增加的目录为:

kernel/fs/yaffs2

实际上，Android包经过编译后生成的system.img和ramdisk.img文件就是yaffs2格式的包.

3. 增加了Android的相关Driver,相应目录为:

kernel/drivers/android

主要分为:

Android IPC系统: Binder (binder.c)

Android 日志系统: Logger (logger.c)

Android 电源管理: Power (power.c)

Android 闹钟管理: Alarm (alarm.c)

Android 内存控制台: Ram_console (ram_console.c)

Android 时钟控制的gpio: Timed_gpio (timed_gpio.c)

4. 增加了switch处理, 相应的目录为:

kernel/drivers/switch/

5. 增加了一种新的共享内存处理方式, 相应增加的文件为:

kernel/mm/ashmem.c

6. 其他为Linux-2.6.25内核所做的补丁等等，例如BlueTooth, 在此不做详细分析

另外GoldFish平台相关的驱动文件如下:

1. 字符输出设备:

kernel/drivers/char/goldfish_tty.c

2. 图象显示设备: (Frame Buffer)

kernel/drivers/video/goldfishfb.c

3. 键盘输入设备:

kernel/drivers/input/keyboard/goldfish_events.c

4. RTC设备: (Real Time Clock)

kernel/drivers/rtc/rtc-goldfish.c

5. USB Device设备:

kernel/drivers/usb/gadget/android_adb.c

6. SD卡设备:

kernel/drivers/mmc/host/goldfish.c

7. FLASH设备:

kernel/drivers/mtd/devices/goldfish_nand.c

kernel/drivers/mtd/devices/goldfish_nand_reg.h

8. LED设备:

kernel/drivers/leds/ledtrig-sleep.c

9. 电源设备:

kernel/drivers/power/goldfish_battery.c

10. 音频设备:

kernel/arch/arm/mach-goldfish/audio.c

11. 电源管理:

kernel/arch/arm/mach-goldfish/pm.c

12. 时钟管理:

kernel/arch/arm/mach-goldfish/timer.c

下面的链接为Android Kernel和标准Linux-2.6.25包相比较所产生的PATCH包， 其中比较小的other patch包是除了上面列出的增加文件之外所修改的文件细节，供大家参考。

http://blogimg.chinaunix.net/blog/upfile2/090102095410.gz

以下为Android内核启动信息：

Uncompressing Linux.................................................................................... done, booting the kernel.

emulator: emulator window was out of view and was recentred

Linux version 2.6.25-00350-g40fff9a (android-build@apa27.mtv.corp.google.com) (gcc version 4.2.1) #1 Wed Jul 23 18:10:44 PDT 2008

CPU: ARM926EJ-S [41069265] revision 5 (ARMv5TEJ), cr=00003137

Machine: Goldfish

Memory policy: ECC disabled, Data cache writeback

CPU0: D VIVT write-through cache

CPU0: I cache: 4096 bytes, associativity 4, 32 byte lines, 32 sets

CPU0: D cache: 65536 bytes, associativity 4, 32 byte lines, 512 sets

Built 1 zonelists in Zone order, mobility grouping on. Total pages: 24384

Kernel command line: qemu=1 console=ttyS0 android.checkjni=1 android.qemud=ttyS1 android.ndns=2

Unknown boot option `android.checkjni=1': ignoring

Unknown boot option `android.qemud=ttyS1': ignoring

Unknown boot option `android.ndns=2': ignoring

PID hash table entries: 512 (order: 9, 2048 bytes)

Console: colour dummy device 80x30

Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)

Inode-cache hash table entries: 8192 (order: 3, 32768 bytes)

Memory: 96MB = 96MB total

Memory: 94268KB available (2380K code, 445K data, 100K init)

Mount-cache hash table entries: 512

CPU: Testing write buffer coherency: ok

net_namespace: 152 bytes

android_power_init

android_power_init done

NET: Registered protocol family 16

NET: Registered protocol family 2

IP route cache hash table entries: 1024 (order: 0, 4096 bytes)

TCP established hash table entries: 4096 (order: 3, 32768 bytes)

TCP bind hash table entries: 4096 (order: 2, 16384 bytes)

TCP: Hash tables configured (established 4096 bind 4096)

TCP reno registered

checking if image is initramfs... it is

Freeing initrd memory: 136K

goldfish_new_pdev goldfish_interrupt_controller at ff000000 irq -1

goldfish_new_pdev goldfish_device_bus at ff001000 irq 1

goldfish_new_pdev goldfish_timer at ff003000 irq 3

goldfish_new_pdev goldfish_rtc at ff010000 irq 10

goldfish_new_pdev goldfish_tty at ff002000 irq 4

goldfish_new_pdev goldfish_tty at ff011000 irq 11

goldfish_new_pdev smc91x at ff012000 irq 12

goldfish_new_pdev goldfish_fb at ff013000 irq 13

goldfish_new_pdev goldfish_audio at ff004000 irq 14

goldfish_new_pdev goldfish_memlog at ff006000 irq -1

goldfish_new_pdev goldfish-battery at ff014000 irq 15

goldfish_new_pdev goldfish_events at ff015000 irq 16

goldfish_new_pdev goldfish_nand at ff016000 irq -1

goldfish_new_pdev goldfish-switch at ff017000 irq 17

goldfish_new_pdev goldfish-switch at ff018000 irq 18

goldfish_pdev_worker registered goldfish-switch

goldfish_pdev_worker registered goldfish-switch

goldfish_pdev_worker registered goldfish_nand

goldfish_pdev_worker registered goldfish_events

goldfish_pdev_worker registered goldfish-battery

goldfish_pdev_worker registered goldfish_memlog

goldfish_audio_probe

goldfish_pdev_worker registered goldfish_audio

goldfish_pdev_worker registered goldfish_fb

goldfish_pdev_worker registered smc91x

goldfish_pdev_worker registered goldfish_tty

goldfish_pdev_worker registered goldfish_tty

goldfish_pdev_worker registered goldfish_rtc

goldfish_pdev_worker registered goldfish_timer

goldfish_pdev_worker registered goldfish_device_bus

goldfish_pdev_worker registered goldfish_interrupt_controller

ashmem: initialized

Installing knfsd (copyright (C) 1996 okir@monad.swb.de).

yaffs Jul 23 2008 18:10:35 Installing.

io scheduler noop registered

io scheduler anticipatory registered (default)

io scheduler deadline registered

io scheduler cfq registered

allocating frame buffer 320 * 480, got ffc10000

Console: switching to colour frame buffer device 40x30

console [ttyS0] enabled

brd: module loaded

loop: module loaded

nbd: registered device at major 43

smc91x.c: v1.1, sep 22 2004 by Nicolas Pitre <nico@cam.org>

No IRQF_TRIGGER set_type function for IRQ 12 (goldfish)

eth0: SMC91C11xFD (rev 1) at c6800000 IRQ 12 [nowait]

eth0: Ethernet addr: 52:54:00:12:34:56

goldfish nand dev0: size 4000000, page 2048, extra 64, erase 131072

goldfish nand dev1: size 4000000, page 2048, extra 64, erase 131072

goldfish nand dev2: size 4000000, page 2048, extra 64, erase 131072

mice: PS/2 mouse device common for all mice

*** events probe ***

events_probe() addr=0xc6804000 irq=16

events_probe() keymap=qwerty2

input: qwerty2 as /class/input/input0

goldfish_rtc goldfish_rtc: rtc core: registered goldfish_rtc as rtc0

logger: created 64K log 'log_main'

logger: created 64K log 'log_events'

logger: created 64K log 'log_radio'

IPv4 over IPv4 tunneling driver

GRE over IPv4 tunneling driver

TCP cubic registered

NET: Registered protocol family 1

NET: Registered protocol family 17

RPC: Registered udp transport module.

RPC: Registered tcp transport module.

802.1Q VLAN Support v1.8 Ben Greear <greearb@candelatech.com>

All bugs added by David S. Miller <davem@redhat.com>

VFP support v0.3: implementor 41 architecture 1 part 10 variant 9 rev 0

goldfish_rtc goldfish_rtc: setting system clock to 2009-01-02 07:43:01 UTC (1230882181)

Freeing init memory: 100K

init: cannot open '/initlogo.rle'

yaffs: dev is 32505856 name is "mtdblock0"

yaffs: passed flags ""

yaffs: Attempting MTD mount on 31.0, "mtdblock0"

yaffs: dev is 32505857 name is "mtdblock1"

yaffs: passed flags ""

yaffs: Attempting MTD mount on 31.1, "mtdblock1"

yaffs: dev is 32505858 name is "mtdblock2"

yaffs: passed flags ""

yaffs: Attempting MTD mount on 31.2, "mtdblock2"

sh: can't access tty; job control turned off

# init: cannot find '/system/bin/playmp3', disabling 'bootsound'

eth0: link up

warning: `rild' uses 32-bit capabilities (legacy support in use)

init: sys_prop: mis-match msg size recieved: -1 expected: 128

从启动信息可以看出，其主CPU为ARM926EJ-S,并非ARM11 CPU, 说明下载的Emulator内核并非是针对G1手机的，估计只是实现了对ARM926EJ-S CPU的模拟。

以上为Android内核的大致分析，希望能给有兴趣的人员以简单帮助。