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Android kernel code merged into mainline

发表于: 2012-01-12   作者:bookjovi   来源:转载   浏览:
摘要:     现在是Linux 3.3的merge window,android的kernel code终于被merge到mainline中了,记得这个问题在一年前就开始讨论android与mainline kernel的分化问题,毕竟android是桌面Linux使用最广泛的distribution版本,把android code merge到mainline中对Linux长期的发

    现在是Linux 3.3的merge window,android的kernel code终于被merge到mainline中了,记得这个问题在一年前就开始讨论android与mainline kernel的分化问题,毕竟android是桌面Linux使用最广泛的distribution版本,把android code merge到mainline中对Linux长期的发展也有好处,当然Google也不希望自己的kernel与mainline kernel越来越远(那样Google的kernel tree维护者会整天merge code,很繁琐)。

    现在merge进的subsystem有:

    ashmem:Anonymous Shared Memory Subsystem

config ASHMEM
        bool "Enable the Anonymous Shared Memory Subsystem"
        default n
        depends on SHMEM || TINY_SHMEM
        help
          The ashmem subsystem is a new shared memory allocator, similar to
          POSIX SHM but with different behavior and sporting a simpler
          file-based API.

    从ashmem代码中可以看出,ashmem的后台仍是通用的share memory

 

    binder:Android Binder IPC Driver

config ANDROID_BINDER_IPC
        bool "Android Binder IPC Driver"
        default n

    Binder在android中非常重要,基本上所有的跨进程通信(service间通信)都是用的binder机制。binder本质上是一种IPC,和fifo,msgqueue,shm一样运行在kernel空间。palm使用的也是openbinder。另一种mobile平台使用的IPC机制是DBUS,DBUS比binder更为人熟知,一般Fedora的机器都安装了dbus,而且时时运行着。

[root@localhost ipc]# ps aux|grep bus

dbus      1835  0.0  0.1  11212   716 ?        Ssl  Jan03   0:02 dbus-daemon --system

root     26552  0.0  0.1   4260   672 pts/1    S+   05:00   0:00 grep bus

 

    logger:Android log driver

    这个subsystem很简单,就是在/dev目录下创建了四个文件:

#define LOGGER_LOG_RADIO        "log_radio"     /* radio-related messages */
#define LOGGER_LOG_EVENTS       "log_events"    /* system/hardware events */
#define LOGGER_LOG_SYSTEM       "log_system"    /* system/framework messages */
#define LOGGER_LOG_MAIN         "log_main"      /* everything else */

    和syslog的7个等级差不多,android的logger实现也很简单,log放在ringbuffer中,ringbuffer的默认大小是256K

 

    lowmemorykiller:

config ANDROID_LOW_MEMORY_KILLER
        bool "Android Low Memory Killer"
        default N
        ---help---
          Register processes to be killed when memory is low

    lowmemorykiller是android中常用的的特性,iphone中也有相同的机制,当内存不够时系统会杀掉一些进程,我以前一直以为android用的是Linux mm的oom_killer,后来想一想应该不是,用Linux mm的oom_killer杀掉进程时系统应该反应已经非常迟钝了,注重用户响应速度的android不会等到那时才杀进程。

    lowmemorykiller的实现原理很简单(200LOC),向mm注册一个shrinker,当系统memory压力比较大时,kswapd会调用shrinker清理内存,用户可以配置一些memory threshold来控制lowmemorykiller的行为。

 

   pmem,ram_console,timed_gpio,timed_output,swich这几个subsystem牵涉到硬件层次比较多,暂未深入了解。

 

    Linux在3.3 merge window中还merge了GNU的mpilib库:

    config MPILIB

        tristate "Multiprecision maths library"
        help
          Multiprecision maths library from GnuPG.
          It is used to implement RSA digital signature verification,
          which is used by IMA/EVM digital signature extension.

config MPILIB_EXTRA
        bool "Multiprecision maths library - additional sources"
        depends on MPILIB
        help
          Multiprecision maths library from GnuPG.
          It is used to implement RSA digital signature verification,
          which is used by IMA/EVM digital signature extension.
          This code in unnecessary for RSA digital signature verification,
          and can be compiled if needed.

config DIGSIG
        tristate "In-kernel signature checker"
        depends on KEYS
        select MPILIB
        help
          Digital signature verification. Currently only RSA is supported.
          Implementation is done using GnuPG MPI library
 

 

 

Android kernel code merged into mainline

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