[Huawei P9 Guides, News, & Discussion] zgfg:
8

It sounds plausible but won't work. I experimented yesterday and today on my P9 (Dual SIM L19 before rebranding to AL10).

Before going to Open Kirin RROS I made backup of everything (apps, settings, etc) in stock Backup app and back up my patched b535 System in adb (will be saved to Internal memory on the phone, to be allowed to call su in adb you must grant root privileges to adb shell when popped up)

adb shell
su
dd if=/dev/block/bootdevice/by-name/system of=/sdcard/mySystem.img

Then I installed RROS (Wipe and Factory reset in Recovery, flashing RROS by Fastboot).

Since ramdisk as patched for Magisk remained intact, I immediately had Magisk working on RROS. Also both SIM cards worked since that patch in Vendor partition remained intact.

When I was going back to b535 I flashed my backup of the patched b535 System in Fastboot

fastboot flash system nySystem.img

And in Recovery Wiped Cache and Factory reset. Btw, this time Recovery was fully in Chinese, thankfully I remembered how it looked in English half a day earlier when going to RROS :)

When I booted to b535 both SIM cards immediately worked, VolTE and Face Unlock were also there.

I restored from Backup app, got all my apps back (some like Mega, MiXPlorer, Telegram etc were completely restored with their settings, some like Skype require to sign in again or so). Home screens with folders and hidden screen were also restored, WiFi APNs, etc. However, PIN, fingers and face must be enrolled again.

Magisk Manager was restored and Magisk worked (root, SafetyNet). I had to install Busy Box and Vanced YouTube i n Background modules again.

Only two issues I was unable to fix:

1) System Update pops up (on reboot) warning of unauthorized changes and asks for Full reinstallation of b535.

Edit: It can be 'solved' by:

- Airplane on

- Settings / Apps / System processes / System Update: Clear Data

- Disable System Update: MixPlorer / root and navigate to /system/app/HWoUC and rename HWoUC.apk to HWoUC.bak

- Reboot

- Airplane off

When you hear that other users are receiving new OTA in future, enable System Update by changing extension for HWoUC from bak to apk

2) Cannot sign in to Google account, even upon flashing again the Playstore patch.

Settings / Accounts / Add Google - before asking me to enter GMail address, app crashes and screen goes black for 5+ seconds and then returns back to Accounts screen.

Even flashing CleanUp patch, rebooting and flashing Playstore patch does not help.

Everything else works just fine as before going to Open Kirin.

I'm thinking what if I also made backup of Data partition in adb (TWRP does not support encryption and hence cannot access Data, whereas System can be backed up and restored by TWRP.

Then I could now flash in Fastboot my backed-up b535 Data (without Factory Resetting in Recovery, only Wiping Cache) - and it would either fully restore my previously patched b535 with all apps and settings (or brick the phone, I don't know is it possible to backup/restore encrypted Data that way and what are the consquences)

PS: Same thing tested with TWRP backup of System partition (I also prepared it before going to Open Kirin) and restoring it through TWRP when going back from Open Kirin.

At the end, result was the same: everything else restored and solved except (1) and (2) - where (2) is actually a showstoper if you need your Google account, eg if you want to use Google Play for downliading and updating applications