Settings: Read defaults from the bundled partition (#2852)

[abranson]

Use ApplicationInfo partition flags to detect whether GmsCore was originally bundled on product or system_ext, and read etc/microg.xml from that partition. Keep /system/etc/microg.xml as a shared defaults source underneath partition-specific overrides.

[mar-v-in]

Any reason to only allow /product/etc/microg.xml when the package is installed on /product? Same for /system_ext?

How do those internal methods (isProduct and isSystemExt) behave when a package that was originally installed in /product or/system_ext is updated by the user?

[abranson]

Any reason to only allow /product/etc/microg.xml when the package is installed on /product? Same for /system_ext?

It was the suggestion here: #2852 (comment) to "first search on the same partition of the apk (whatever it is) and then fallback to system." and I thought that made a lot of sense. If we bundle then it should all be in the same partition. Falling back to system is only needed for backwards compat, but I think that's necessary.

How do those internal methods (isProduct and isSystemExt) behave when a package that was originally installed in /product or/system_ext is updated by the user?

There isn't any public docs that I found for those, but I couldn't use sourceDir precisely because it does not preserve the original installed location. These flags do get preserved: https://android.googlesource.com/platform/frameworks/base/+/refs/heads/main/services/core/java/com/android/server/pm/InstallPackageHelper.java#2101
They are hidden API, but I think it's exactly what they're used for.

[ale5000-git]

@mar-v-in
On Android various standard Android xml files are restricted to the same partition, so I think it make sense to follow the trend.

Also I suggest to change the path to /<partition-name>/etc/<package-name>/settings.xml => example: /product/etc/com.google.android.gms/settings.xml, and use /system/etc/microg.xml only as final fallback.
In this way a fork with a different package name (at compile time) would have a different path.

[abranson]

Now it checks /$partition/etc/$packageName/settings.xml, then /$partition/etc/microg.xml, and finally /system/etc/microg.xml. I've seen anticipation of /$partition/etc/microg.xml so I thought it would be nice to leave that in.