We want to use ext4 images to enable delta updates for complex DLC candidates like ARC++. The issue with building ext4 images when emerging a DLC package is that we require rw access to the loop devices in /dev/, which results in sandbox violations.

One way we can work around this is to add the relevant loop device (e.g. /dev/loop-control and /dev/loop1) to the sandbox. This works in the simple case where we want to build a single DLC, but since builds are parallelized, we can't be sure which loop device we will end up using.