Android P(9.0) userdebug版本执行adb remount失败

[DESCRIPTION]

     在android P版本上如果按照“FAQ18076 android 6.0 M userdebug版本执行adb remount失败”的做法在userdebug版本上执行adb remount会提示以下错误：

remount of the / superblock failed: Permission denied
remount failed

     原因是android P版本后google启用avb(Android Verified Boot)2.0，verified boot and DM-verity默认启用策略发生了变化。详情如下：

DM-Verity behavior changes from vboot1.0 to avb2.0.

On vboot1.0, dm-verity is turned off on eng build and is enabled on userdebug/user build.
DM-verity could be disabled with adb (not fastboot) on userdebug build without unlocking device first.
DM-Verity could not be disabled on user build.
On avb2.0, dm-verity behavior are the same on all build variants.
It's turned on by default and could only be disabled after device is unlocked.
dm-verity disable flag is moved from system image dm-verity metadata(vboot1.0) to vbmeta image(avb2.0), and you have two ways to disable it: adb and fastboot.

  

* Android P + kernel-4.4 or kernel-3.18
- download preloader with verified boot disabled which location is the same as scatter file //preloader_<PROJECT>_SBOOT_DIS.bin
- adb root
- adb disable-verity
- adb reboot
- adb root
- adb remount

* Android P + kernel-4.9 or after
- download preloader with verified boot disabled which location is the same as scatter file. //preloader_<PROJECT>_SBOOT_DIS.bin
- boot to Home Screen
- go to setting -> system -> Developer options -> OEM unlocking
- adb reboot bootloader
- fastboot flashing unlock
- press volume up key
- fastboot reboot
- adb root
- adb disable-verity
- adb reboot
- adb root
- adb remount

After Android P, preloader_<PROJECT>_SBOOT_DIS.bin will be generated automatically after building preloader.

Windows
https://dl.google.com/android/repository/platform-tools-latest-windows.zip
Mac
https://dl.google.com/android/repository/platform-tools-latest-darwin.zip
Linux
https://dl.google.com/android/repository/platform-tools-latest-linux.zip