Look into splitting up container mounts intelligently

[pdsouza]

/ should be mounted on /system but we would need a way to get around the fact that it is "ro". This would be good since we wouldn't need to remove the "nosuid" flag from /data.

/home should be mounted on /data/media. This would make it easier for users to upgrade Maru without having to back up their desktop data. They could use TWRP factory reset and still preserve their desktop /home directory.

[utzcoz]

@pdsouza What about Overlay filesystem? Make root readonly, and add a directory in /data/media or /data/overlayfs to overlay the root directory of desktop. After that, all modification of desktop will saved in /data. With /data/media, all modification of user will stored in /data for a better experience to upgrade Maru. I have saw some system doing similar things.

[pdsouza]

@utzcoz Oh wow, overlayfs looks very cool. This could solve our problem. Do you know if this is available on Android kernels? Do we need a minimum kernel version to support overlayfs?

[utzcoz]

@pdsouza I have search overlayfs in nexus 5x's kernel code, but there doesn't have some result about overlayfs. Sorry.

[meiser79]

Removing the "nosuid" flag from /data causes a SafetyNet failure. Therefore, an overlay solution is much appreciated.

[utzcoz]

The Android 10 integrates Overlayfs to Android official.

1. Android Overlayfs integration with adb remount
2. Android 10 Release notes - Overlayfs

[pdsouza]

@utzcoz This is great news. We still have the kernel requirements for overlayfs so I guess we can only use this approach with modern kernels (3.18+). The legacy devices like N5 will have to continue to use nosuid unless overlayfs can be backported. But this is a great approach for all new devices.

I wonder if we can experiment with this in Android 9 too? I will be porting Maru up to Android 9 / LineageOS 16 soon. I think it will be sometime before Android 10 / LineageOS 17 is out and stable. But maybe we can experiment with Android 10 on pure AOSP with Pixel devices to prototype this.

[utzcoz]

@pdsouza Okay, I can help test it with Android 10 on pure AOSP with Pixel(Sailfish). If I have some updates, I will post them to this issue to discuss.