Magisk: [Android10] A-only two stage system-as-root

[argraur]

https://source.android.com/devices/bootloader/system-as-root

Android 10 forces system-as-root for all devices now, on non-A/B devices, both recovery and boot partitions exist, but boot partition contains ramdisk with init and base mount points

System boots in two stages. Kernel starts with boot-ramdisk as ramdisk and executes first stage init (/init) that mounts system, chroots into it and executes /system/bin/init (second stage init) that starts Android system.

A-only boot-ramdisk layout:
/apex (folder)
/avb (folder)
/debug_ramdisk (folder)
/dev (folder, mount point)
/init (static executable)
/mnt (folder, mount point)
/proc (folder, mount point)
/sys (folder, mount point)

_Magisk currently can't handle these boot-ramdisks_.

[topjohnwu]

I'm well aware of 2 stage boot since that is what Pixel 3 Android 10 uses (whilst being A/B). A completely new process of booting is introduced into magiskinit to support it. I do not have any device that is A-only, so I'm not so sure about why it isn't working. Are you testing on the latest canary?

[argraur]

Yes.

[topjohnwu]

Wait, there is no folder called /first_stage_ramdisk in the ramdisk? I though the standard process is to chroot into that folder, mount systems, and finally chroot again into /system. Magisk uses that to indicate that 2 stage init is used.

[topjohnwu]

May you upload the boot image? I need to see how to patch fstab in this case....

[argraur]

It sure doesn't. On A/B devices first_stage_ramdisk is used to get rid of recovery components, but A-only mounts and chroots to system directly.

[argraur]

Sure

[argraur]

https://drive.google.com/file/d/1-QAw3Fyl6fWiFjMXTqQOV29v9kKJF4kO/view?usp=drivesdk

[argraur]

Looks like it uses fstab in dts :/

[topjohnwu]

Looks like it uses fstab in dts :/

Well, that's some bad news......
I have to modify the fstab to change the folder from /system to anything else, or else the original init will continue to proceed and we have no way to stop it 😅
On the Pixels, the fstab is simply just a file in /first_stage_ramdisk, which is super simple

[topjohnwu]

BTW, nice avatar you're using @argraur. Really like Momo 😉

[argraur]

Oof thanks <3

[argraur]

By the way, system can be mounted as r/w on A-only devices.

[topjohnwu]

@argraur I think you are currently using custom ROM. On stock ROMs, the system image is formatted as "ext4 dedup", which is not possible to mount r/w. Check my tweets to see more info about this.

[xyyx]

https://source.android.com/devices/bootloader/system-as-root

Android 10 forces system-as-root for all devices now, on non-A/B devices, both recovery and boot partitions exist, but boot partition contains ramdisk with init and base mount points

System boots in two stages. Kernel starts with boot-ramdisk as ramdisk and executes first stage init (/init) that mounts system, chroots into it and executes /system/bin/init (second stage init) that starts Android system.

A-only boot-ramdisk layout:
/apex (folder)
/avb (folder)
/debug_ramdisk (folder)
/dev (folder, mount point)
/init (static executable)
/mnt (folder, mount point)
/proc (folder, mount point)
/sys (folder, mount point)

_Magisk currently can't handle these boot-ramdisks_.

Superuser is alive) Still alive) But I am waiting for Magisk)

[h0cheung]

https://source.android.com/devices/bootloader/system-as-root
Android 10 forces system-as-root for all devices now, on non-A/B devices, both recovery and boot partitions exist, but boot partition contains ramdisk with init and base mount points
System boots in two stages. Kernel starts with boot-ramdisk as ramdisk and executes first stage init (/init) that mounts system, chroots into it and executes /system/bin/init (second stage init) that starts Android system.
A-only boot-ramdisk layout:
/apex (folder)
/avb (folder)
/debug_ramdisk (folder)
/dev (folder, mount point)
/init (static executable)
/mnt (folder, mount point)
/proc (folder, mount point)
/sys (folder, mount point)
_Magisk currently can't handle these boot-ramdisks_.

Superuser is alive) Still alive) But I am waiting for Magisk)

How to use it? I tried to copy file from phh's superuser but it doesn't work.

[argraur]

@topjohnwu I just tried to mount K20 Pro Android 10 system image as r/w and it worked! http://bigota.d.miui.com/9.05.24/raphael_android_images_9.05.24.1.native.google.user_20190524.0000.00_10.0_ab58fbe3cb.tgz

[half-cambodian-hacker-man]

@topjohnwu Since this is becoming a blocker as more devices adopt Android 10, would it be worth funding an A-only Q-capable device for your testing?

[jmac052002]

I would definitely throw in to fund an A-only device for testing!

[argraur]

There are no A-only devices launched with Q. There are Mi 9 and K20 Pro that got official Q but both of them have Pie system-as-root implementation.

[skittles9823]

John has a Nexus 5X which just got Pixel Experience 10 so now that he's released the new Magisk 19.4 beta he will probably start on seeing what's up with A only SAR on Q.

[aleasto]

To elaborate on some comments above:
A-only 2 stage init SAR can work both by including an fstab in the first stage ramdisk where the fstab contains /system with the flag first_stage_mount( reference article https://source.android.com/devices/architecture/kernel/mounting-partitions-early#fstab-ramdisk ), OR by early-mounting the /system block in dts fstab (note that the article does NOT say this is a possible solution!)
The second approach is the trend custom roms are going to follow for supporting legacy devices (before the legacy-SAR era), while the first one is most likely going to be used by vendors who are willing to release devices on Q with A-only SAR.
Idealy you'd want to support both, but the fstab patching would get quite complex.

[topjohnwu]

These series of commits add support for A-only 2SI devices: 4d91e50d6dec76a4bdcec737f11d7547b0da34cb...cf2d02c0dddbaaaa2b50b71369f8c8e5aa143b55

[AlexZorzi]

I'm still facing bootloops after installing latest magisk canary on s8 lineage 17.0 exynos 8995. uploading pstore logs can be useful?