The way how logical partition, or "Logical Resizable Android Partitions"
as they say in AOSP source code, is setup makes it impossible to early
mount the partitions from the shared super partition with just
a few lines of code; in fact, AOSP has a whole "fs_mgr" folder which
consist of multiple complex libraries, with 15K lines of code just
to deal with the device mapper shenanigans.
In order to keep the already overly complicated MagiskInit more
managable, I chose NOT to go the route of including fs_mgr directly
into MagiskInit. Luckily, starting from Android Q, Google decided to
split init startup into 3 stages, with the first stage doing _only_
early mount. This is great news, because we can simply let the stock
init do its own thing for us, and we intercept the bootup sequence.
So the workflow can be visualized roughly below:
Magisk First Stage --> First Stage Mount --> Magisk Second Stage --+
(MagiskInit) (Original Init) (MagiskInit) +
+
+
...Rest of the boot... <-- Second Stage <-- Selinux Setup <--+
(__________________ Original Init ____________________)
The catch here is that after doing all the first stage mounting, /init
will pivot /system as root directory (/), leaving us impossible to
regain control after we hand it over. So the solution here is to patch
fstab in /first_stage_ramdisk on-the-fly to redirect /system to
/system_root, making the original init do all the hard work for
us and mount required early mount partitions, but skips the step of
switching root directory. It will also conveniently hand over execution
back to MagiskInit, which we will reuse the routine for patching
root directory in normal system-as-root situations.
- Magisk "dirty" flashes would remove the /overlay directory which might have been put there by a custom kernel or other mod
- this is a leftover from when Magisk itself used /overlay for placing init.magisk.rc, so just remove this file specifically and leave the rest intact
- correct 'booloader' typo breaking bootloader entry
- remove extra bootloader entry Shell.su line which is unnecessary since it's covered by reboot()
- revert to using `reboot recovery` for recovery entry since `svc power reboot recovery` triggers a very disconcerting "Factory data reset" reboot dialog on many devices
- add Reboot to EDL mode option for good measure
The current system-as-root magiskinit implementation (converting
root directory in system partition to legacy rootfs setup) is now
considered as backwards compatible only.
The new implementation that is hide and Android Q friendly is coming soon.
