Android 4.4 Kitkat 使能 USB adb 功能

背景

在 Linux-3.8 以后，Android 的内核分支，便去掉了 f_adb，改使用 USB function FS，在用户空间实现 USB adb 功能。这篇文章依据原作者的 Google+ 文章，在 Atmel sama5 开发板上做了測试，将步骤记录例如以下，供须要使用的读者參考，你也能够查看作者原文：https://plus.google.com/111524780435806926688/posts/AaEccFjKNHE 

在 Linux-3.10 上使能 USB ADB

编译内核时使能 USB FunctionFS

When building your kernel, make sure to configure in FunctionFS:
    Device Drivers -> USB Support -> USB Gadget Support
        -> USB Gadget Driver -> Function Filesystem

设置正确的 USB vendor ID 和 Product ID

这个设置能够放在 bootcmd 或者载入内核模块的时候通过參数传递：

Modify your boot parameters to set the vendor and product ids so adb on your host recognizes the device.
    g_ffs.idVendor=0x18d1 g_ffs.idProduct=0x4e26

Alternatively this can also be done if you built the gadget driver as a module at load time:

    insmod g_ffs.ko idVendor=0x18d1 idProduct=0x4e26

启动 Android 并挂载 functionFS， 使能 USB adb

Now here I'm assuming you've got a serial port working. Boot your target device with your new kernel (and insmod the g_ffs driver if necessary), and setup the functionfs directory:

    # mkdir /dev/usb-ffs
    # mkdir /dev/usb-ffs/adb
    # mount -o uid=2000,gid=2000 -t functionfs adb /dev/usb-ffs/adb

重新启动 adbd 守护进程

If everything is working, you can kill adbd and when it restarts it should find the functionfs mount and make use of it.

    # ps adbd
    # kill <pid for adbd>

然后进入 cmd 或者 Linux Host 就能够成功连接 usb adb 获得 Android shell 了

On your host system, connect to the target using the adb program:

    $ ./adb shell
    root@android:/#

    Hooray there's your shell!