在Ubuntu上为Android 10 系统内置C可执行程序测试Linux内核驱动程序

学习总纲：

Android10 硬件抽象层（HAL）概要介绍和学习计划

编译环境：

   - android 版本 - android-10.0.0_r41
   - 架构 - aosp_x86_64-eng
   - 内核分支：android-goldfish-4.14-gchips

参考教材：

 罗升阳：https://blog.youkuaiyun.com/luoshengyang/article/details/6571210
 
 依赖前文：https://blog.youkuaiyun.com/silently_frog/article/details/124184244

目的

记录android 10 用老罗的方法编译后出现的问题和修改当法

修改点如下：

1. hello.c 中缺少头文件

#include <unistd.h>

2. Android.mk 中缺少取消-Werror,-Wunused-parameter 警告

LOCAL_CFLAGS += -Wno-unused-parameter

3. 特有问题：
   按照老罗的步骤：

       mmm ./external/hello
   在out/target/product/generic_x86_64/system/bin目录下，生存了hello文件

       make snod
   将其打包到system.img中，运行模拟器：
       emulator -kernel ./goldfish/arch/x86/boot/bzImage

   发现system/bin下面没有hello的测试程序

   解决方法：
   方法1： 执行全编译

   make -j8

   方法2：手动push
       adb push ./out/target/product/generic_x86_64/system/bin/hello system/bin
   
   按照网上的方法执行：adb remount 重新挂载文件系统，获得可写的权限。但是发生了如下错误：

adb remount 挂载不上

Skip mounting partition: /product
Skip mounting partition: /product_services
Skip mounting partition: /product
Skip mounting partition: /product_services
Skip mounting partition: /product
Skip mounting partition: /product_services
W DM_DEV_STATUS failed for scratch: No such device or address
E [liblp]No device named scratch
[liblp]Partition scratch will resize from 0 bytes to 820367360 bytes
E [liblp]bool android::fs_mgr::WritePrimaryMetadata(int, const android::fs_mgr::LpMetadata &, uint32_t, const std::string &, const std::function<bool (int, const std::string &)> &) write 540 bytes failed: Operation not permitted
E [libfs_mgr]add partition scratch
Skip mounting partition: /product
Skip mounting partition: /product_services
...
W DM_DEV_STATUS failed for scratch: No such device or address
E [liblp]No device named scratch
[liblp]Partition scratch will resize from 0 bytes to 820367360 bytes
E [liblp]bool android::fs_mgr::WritePrimaryMetadata(int, const android::fs_mgr::LpMetadata &, uint32_t, const std::string &, const std::function<bool (int, const std::string &)> &) write 540 bytes failed: Operation not permitted
E [libfs_mgr]add partition scratch
Skip mounting partition: /product
Skip mounting partition: /product_services
...
W DM_DEV_STATUS failed for scratch: No such device or address
Skip mounting partition: /product
Skip mounting partition: /product_services
E Can not mount overlayfs for partitions: No such file or directory
Skip mounting partition: /product
Skip mounting partition: /product_services
E failed to remount partition dev:/dev/block/dm-0 mnt:/: Read-only file system
E Consider providing all the dependencies to enable overlayfs
E failed to remount partition dev:/dev/block/dm-1 mnt:/vendor: Read-only file system
E Consider providing all the dependencies to enable overlayfs
/system/bin/remount exited with status 10
remount failed

解决方法：运行模拟器时添加 “-writable-system”

如:

1. emulator -kernel ./goldfish/arch/x86/boot/bzImage -writable-system
2. adb root
3. adb disable-verity
4. adb reboot
5. adb root
6. adb remount
7. adb shell
8. mount -o rw,remount /system
9. adb push ./out/target/product/generic_x86_64/system/bin/hello system/bin