Adding new directories and data in Custom android image

Hello,

I'm trying to add extra directories and data in the android rom, before the first run of the rom.

When extracting the boot.img, it looks like data from a location is copied into the riotboard when booting.

This looks like the following:

/adb_keys     u:object_r:rootfs:s0

I would like to get extra files to such a location and add it while booting.

But how to do this?

Best regards,
Floris