Android kernel和標準Linux Kernel的差異

在這裏 http://www.linuxfordevices.com/c/a/Linux-For-Devices-Articles/Porting-Android-to-a-new-device/ 發現一篇分析Android kernel與標準kernel的差異的文章，但是，作者用的是2.6.25的內核，我發現在Android2.6.29內核中，與之前相比，有了很多改變，因此在上面link中的文章的基礎上，重新分析了2.6.29版本的Android kernel和標準kernel的區別。

總的區別可以歸納如下：

• ARCH --  這是Android修改了arch/arm下面的一些文件：

  arch/arm:

  Chg: arch/arm/kernel/entry-armv.S

  Chg: arch/arm/kernel/module.c

  Chg: arch/arm/kernel/process.c

  Chg: arch/arm/kernel/ptrace.c

  Chg: arch/arm/kernel/setup.c

  Chg: arch/arm/kernel/signal.c

  Chg: arch/arm/kernel/traps.c

  Chg: arch/arm/mm/cache-v6.S

  Chg: arch/arm/vfp/entry.S

  Chg: arch/arm/vfp/vfp.h

  Chg: arch/arm/vfp/vfphw.S

  Chg: arch/arm/vfp/vfpmodule.c

Goldfish --  這是Android爲了模擬器所開發的一個虛擬硬件平臺。Goldfish執行arm926T指令（在2.6.29中，goldfish也支持ATMv7指令），但是在實際的設備中，該虛擬平臺的文件不會被編譯。

arch/arm/mach-goldfish:

New: arch/arm/mach-goldfish/audio.c

New: arch/arm/mach-goldfish/board-goldfish.c

New: arch/arm/mach-goldfish/pdev_bus.c

New: arch/arm/mach-goldfish/pm.c

New: arch/arm/mach-goldfish/switch.c

New: arch/arm/mach-goldfish/timer.c

YAFFS2 --  和PC把文件存儲在硬盤上不一樣， 移動設備一般把Flash作爲存儲設備。尤其是NAND flash應用非常廣泛（絕大多數手機用的都是NAND flash，三星的一些手機使用的是OneNAND）。NAND flash具有低成本和高密度的優點。

YAFFS2 是“Yet Another Flash File System, 2nd edition" 的簡稱。 它提供在Linux內核和NAND flash設備 之前高效率的接口。 YAFFS2並沒有包含在標準的Linux內核中， Google把它添加到了Android的kernel

fs/yaffs2:

New: fs/yaffs2/devextras.h

New: fs/yaffs2/Kconfig

New: fs/yaffs2/Makefile

New: fs/yaffs2/moduleconfig.h

New: fs/yaffs2/yaffs_checkptrw.c

New: fs/yaffs2/yaffs_checkptrw.h

New: fs/yaffs2/yaffs_ecc.c

New: fs/yaffs2/yaffs_ecc.h

New: fs/yaffs2/yaffs_fs.c

New: fs/yaffs2/yaffs_getblockinfo.h

New: fs/yaffs2/yaffs_guts.c

New: fs/yaffs2/yaffs_guts.h

New: fs/yaffs2/yaffsinterface.h

New: fs/yaffs2/yaffs_mtdif1.c

New: fs/yaffs2/yaffs_mtdif1.h

New: fs/yaffs2/yaffs_mtdif2.c

New: fs/yaffs2/yaffs_mtdif2.h

New: fs/yaffs2/yaffs_mtdif.c

New: fs/yaffs2/yaffs_mtdif.h

New: fs/yaffs2/yaffs_nand.c

New: fs/yaffs2/yaffs_nandemul2k.h

New: fs/yaffs2/yaffs_nand.h

New: fs/yaffs2/yaffs_packedtags1.c

New: fs/yaffs2/yaffs_packedtags1.h

New: fs/yaffs2/yaffs_packedtags2.c

New: fs/yaffs2/yaffs_packedtags2.h

New: fs/yaffs2/yaffs_qsort.c

New: fs/yaffs2/yaffs_qsort.h

New: fs/yaffs2/yaffs_tagscompat.c

New: fs/yaffs2/yaffs_tagscompat.h

New: fs/yaffs2/yaffs_tagsvalidity.c

New: fs/yaffs2/yaffs_tagsvalidity.h

New: fs/yaffs2/yportenv.h

• Bluetooth --  Google爲Bluetooth打上了patch，fix了一些Bluetooth的bug

  drivers/bluetooth:

Chg: drivers/bluetooth/bfusb.c

Chg: drivers/bluetooth/bt3c_cs.c

Chg: drivers/bluetooth/btusb.c

Chg: drivers/bluetooth/hci_h4.c

Chg: drivers/bluetooth/hci_ll.c

• Scheduler --  對於Scheduler的改變非常小，我對它並沒有去研究。

  Chg: kernel/sched.c

New Android Functionality --  除了fix一些bug以及其他一些小的更改，Android增加了一些新的功能，介紹如下：

• IPC Binder -- The IPC Binder is an Inter-Process Communication (IPC) mechanism. It allows processes to provide services to other processes via a set of higher-level APIs than are available in standard Linux. An Internet search indicated that the Binder concept originated at Be, Inc., and then made its way into Palm's software, before Google wrote a new Binder for Android.

New: drivers/staging/android/binder.c

• • Low Memory Killer -- Android adds a low-memory killer that, each time it's called, scans the list of running Linux processes, and kills one. It was not clear in our cursory examination why Android adds a low-memory killer on top of the already existing one in the standard Linux kernel.

    New: drivers/staging/android/lowmemorykiller.c

• Ashmem -- Ashmem is an Anonymous SHared MEMory system that adds interfaces so processes can share named blocks of memory. As an example, the system could use Ashmem to store icons, which multiple processes could then access when drawing their UI. The advantage of Ashmem over traditional Linux shared memory is that it provides a means for the kernel to reclaim these shared memory blocks if they are not currently in use. If a process then tries to access a shared memory block the kernel has freed, it will receive an error, and will then need to reallocate the block and reload the data.

  New: mm/ashmem.c

RAM Console and Log Device -- To aid in debugging, Android adds the ability to store kernel log messages to a RAM buffer. Additionally, Android adds a separate logging module so that user processes can read and write user log messages. 

New: drivers/staging/android/ram_console.c

Android Debug Bridge -- Debugging embedded devices can best be described as challenging. To make debugging easier, Google created the Android Debug Bridge (ADB), which is a protocol that runs over a USB link between a hardware device running Android and a developer writing applications on a desktop PC. 

drivers/usb/gadget:

New: drivers/usb/gadget/android.c

Chg: drivers/usb/gadget/composite.c

Chg: drivers/usb/gadget/f_acm.c

New: drivers/usb/gadget/f_acm.h

New: drivers/usb/gadget/f_adb.c

New: drivers/usb/gadget/f_adb.h

New: drivers/usb/gadget/f_mass_storage.c

New: drivers/usb/gadget/f_mass_storage.h

Android also adds a new real-time clock, switch support, and timed GPIO support. We list the impacted files for these new modules at the end of this document.

 

Power Management --  Power management is one of the most difficult pieces to get right in mobile devices, so we split it out into a group separate from the other pieces. It's interesting to note that Google added a new power management system to Linux, rather than reuse what already existed. We list the impacted files at the end of this document.

kernel/power:

New: kernel/power/consoleearlysuspend.c

New: kernel/power/earlysuspend.c

New: kernel/power/fbearlysuspend.c

Chg: kernel/power/main.c

Chg: kernel/power/power.h

Chg: kernel/power/process.c

New: kernel/power/userwakelock.c

New: kernel/power/wakelock.c

• Miscellaneous Changes --  In addition to the above, we found a number of changes that could best be described as, 'Miscellaneous.' Among other things, these changes include additional debugging support, keypad light controls, and management of TCP networking.

附： 差異表：

arch/arm:
    Chg: arch/arm/kernel/entry-armv.S
    Chg: arch/arm/kernel/module.c
    Chg: arch/arm/kernel/process.c
    Chg: arch/arm/kernel/ptrace.c
    Chg: arch/arm/kernel/setup.c
    Chg: arch/arm/kernel/signal.c
    Chg: arch/arm/kernel/traps.c
    Chg: arch/arm/mm/cache-v6.S
    Chg: arch/arm/vfp/entry.S
    Chg: arch/arm/vfp/vfp.h
    Chg: arch/arm/vfp/vfphw.S
    Chg: arch/arm/vfp/vfpmodule.c

arch/arm/mach-goldfish:
    New: arch/arm/mach-goldfish/audio.c
    New: arch/arm/mach-goldfish/board-goldfish.c
    New: arch/arm/mach-goldfish/pdev_bus.c
    New: arch/arm/mach-goldfish/pm.c
    New: arch/arm/mach-goldfish/switch.c
    New: arch/arm/mach-goldfish/timer.c

block:
    Chg: block/blk-core.c
    Chg: block/genhd.c

drivers/base/power:
    Chg: drivers/base/power/main.c

drivers/bluetooth:
    Chg: drivers/bluetooth/bfusb.c
    Chg: drivers/bluetooth/bt3c_cs.c
    Chg: drivers/bluetooth/btusb.c
    Chg: drivers/bluetooth/hci_h4.c
    Chg: drivers/bluetooth/hci_ll.c

drivers/char:
    New: drivers/char/dcc_tty.c
    New: drivers/char/goldfish_tty.c
    Chg: drivers/char/mem.c

drivers/cpufreq:
    Chg: drivers/cpufreq/cpufreq_conservative.c
    Chg: drivers/cpufreq/cpufreq_ondemand.c

drivers/i2c:
    New: drivers/i2c/chips/pca963x.c

drivers/input:
    Chg: drivers/input/evdev.c
    Chg: drivers/input/input.c
    New: drivers/input/keyboard/goldfish_events.c
    New: drivers/input/keyreset.c
    New: drivers/input/misc/gpio_axis.c
    New: drivers/input/misc/gpio_event.c
    New: drivers/input/misc/gpio_input.c
    New: drivers/input/misc/gpio_matrix.c
    New: drivers/input/misc/gpio_output.c
    New: drivers/input/misc/keychord.c
    New: drivers/input/touchscreen/synaptics_i2c_rmi.c

drivers/leds:
    New: drivers/leds/ledtrig-sleep.c

drivers/misc:
    New: drivers/misc/apanic.c
    New: drivers/misc/kernel_debugger.c
    New: drivers/misc/pmem.c
    New: drivers/misc/qemutrace
    New: drivers/misc/uid_stat.c
    New: drivers/misc/wl127x-rfkill.c

drivers/mmc:
    Chg: drivers/mmc/card/block.c
    Chg: drivers/mmc/core/bus.c
    Chg: drivers/mmc/core/core.c
    Chg: drivers/mmc/core/debugfs.c
    Chg: drivers/mmc/core/sd.c
    Chg: drivers/mmc/core/sdio_bus.c
    Chg: drivers/mmc/core/sdio.c
    Chg: drivers/mmc/core/sdio_io.c
    New: drivers/mmc/host/goldfish.c

drivers/mtd:
    New: drivers/mtd/devices/goldfish_nand.c
    New: drivers/mtd/devices/goldfish_nand_reg.h
    Chg: drivers/mtd/nand/nand_base.c

drivers/net:
    New: drivers/net/pppolac.c
    New: drivers/net/pppopns.c

drivers/power:
    New: drivers/power/goldfish_battery.c

drivers/rtc:
    New: drivers/rtc/alarm.c
    Chg: drivers/rtc/class.c
    New: drivers/rtc/rtc-goldfish.c

drivers/serial:
    Chg: drivers/serial/serial_core.c

drivers/staging/android:
    New: drivers/staging/android/binder.c
    New: drivers/staging/android/lowmemorykiller.c
    New: drivers/staging/android/ram_console.c
    New: drivers/staging/android/timed_gpio.c
    New: drivers/staging/android/timed_gpio.h
    New: drivers/staging/android/timed_output.c
    New: drivers/staging/android/timed_output.h

drivers/switch:
    New: drivers/switch/switch_class.c
    New: drivers/switch/switch_gpio.c

drivers/usb/gadget:
    New: drivers/usb/gadget/android.c
    Chg: drivers/usb/gadget/composite.c
    Chg: drivers/usb/gadget/f_acm.c
    New: drivers/usb/gadget/f_acm.h
    New: drivers/usb/gadget/f_adb.c
    New: drivers/usb/gadget/f_adb.h
    New: drivers/usb/gadget/f_mass_storage.c
    New: drivers/usb/gadget/f_mass_storage.h

drivers/video:
    New: drivers/video/goldfishfb.c

fs:
    Chg: fs/exec.c
    Chg: fs/fat/cache.c
    Chg: fs/fat/dir.c
    Chg: fs/fat/fatent.c
    Chg: fs/fat/fat.h
    Chg: fs/fat/file.c
    Chg: fs/fat/inode.c
    Chg: fs/fat/misc.c
    Chg: fs/fat/namei_msdos.c
    Chg: fs/fat/namei_vfat.c
    Chg: fs/fs-writeback.c
    Chg: fs/partitions/check.c
    Chg: fs/proc/base.c

fs/yaffs2/:

kernel:
    Chg: kernel/cgroup.c
    Chg: kernel/cgroup_freezer.c
    Chg: kernel/cpuset.c
    Chg: kernel/exit.c
    Chg: kernel/fork.c
    Chg: kernel/futex.c
    Chg: kernel/panic.c
    Chg: kernel/posix-cpu-timers.c
    Chg: kernel/printk.c
    Chg: kernel/ptrace.c
    Chg: kernel/sched.c
    Chg: kernel/sysctl.c
    Chg: kernel/time/tick-sched.c

kernel/power:
    New: kernel/power/consoleearlysuspend.c
    New: kernel/power/earlysuspend.c
    New: kernel/power/fbearlysuspend.c
    Chg: kernel/power/main.c
    Chg: kernel/power/power.h
    Chg: kernel/power/process.c
    New: kernel/power/userwakelock.c
    New: kernel/power/wakelock.c

lib:
    Chg: lib/genalloc.c

mm:
    New: mm/ashmem.c
    Chg: mm/mmap.c
    Chg: mm/page_alloc.c
    Chg: mm/shmem.c

net:
    Chg: net/bluetooth/af_bluetooth.c
    Chg: net/bluetooth/cmtp/core.c
    Chg: net/bluetooth/hci_conn.c
    Chg: net/bluetooth/hci_core.c
    Chg: net/bluetooth/hci_event.c
    Chg: net/bluetooth/hci_sysfs.c
    Chg: net/bluetooth/l2cap.c
    Chg: net/bluetooth/rfcomm/core.c
    Chg: net/bluetooth/rfcomm/sock.c
    Chg: net/bluetooth/sco.c
    Chg: net/core/dev.c
    Chg: net/ipv4/af_inet.c
    Chg: net/ipv4/devinet.c
    New: net/ipv4/sysfs_net_ipv4.c
    Chg: net/ipv4/tcp_ipv4.c
    Chg: net/ipv6/af_inet6.c
    Chg: net/rfkill/rfkill.c
    Chg: net/socket.c

security:
    Chg: security/commoncap.c
    Chg: security/security.c

本文出自 “Mobile and Linux Deve..” 博客，請務必保留此出處http://buaadallas.blog.51cto.com/399160/377436