Linux kernel has powerful features, however sometimes it can be disappointing when you discover that trivial details do not work or do not work the very obvious way. Such an example is the loop back device. You may mount a file as a loop back device, but you cannot access its partition as “sub-devices” like it happens with the physical discs. There are workarounds by mounting the partition knowing the start and length of it, but that might be a bit risky.