• topjohnwu's avatar
    Force init to load fstab from file in 2SI · dbf8c412
    topjohnwu authored
    Patching DTBs is proven to be difficult and problematic as there are
    tons of different formats out there. Adding support for all the formats
    in magiskboot has been quite an headache in the past year, and it still
    definitely does not cover all possible cases of them out there.
    
    There is another issue: fake dt fstabs. Some super old devices do not
    have device trees in their boot images, so some custom ROM developers
    had came up with a "genius" solution: hardcode fstab entries directly
    in the kernel source code and create fake device tree nodes even if
    Android 10+ init can graciously take fstab files instead (-_-) 。。。
    
    And there is YET another issue: DTBs are not always in boot images!
    Google is crazy enough to litter DTBs all over the place, it is like
    they cannot make up their minds (duh). This means the dt fstabs can be
    either concatnated after the kernel (1), in the DTB partition (2), in
    the DTBO partition (3), in the recovery_dtbo section in boot images (4),
    or in the dtb section in boot images (5). FIVE f**king places, how can
    anyone keep up with that!
    
    With Android 10+ that uses 2 stage inits, it is crutual for Magisk to
    be able to modify fstab mount points in order to let the original init
    mount partitions for us, but NOT switch root and continue booting. For
    devices using dt for early mount fstab, we used to patch the DTB at
    install time with magiskboot. However these changes are permanent and
    cannot be restored back at reinstallation.
    
    With this commit, Magisk will read dt fstabs and write them to ramdisk
    at boot time. And in that case, the init binary will also be patched
    to force it to NEVER use fstabs in device-tree. By doing so, we can
    unify ramdisk based 2SI fstab patching as basically we are just patching
    fstab files. This also means we can manipulate fstab whatever Magisk
    needs in the future without the need to going through the headache that
    is patching DTBs at installation.
    dbf8c412
init.hpp 3.65 KB