Notes:
There is (should be, don't know the behavior of your Busybox build) a: "find next free" loop device option.
No need to hard code which one to use, lots of reasons to not do so.
Yes, the loop driver can operate as a device-device layer, not just as a file-device layer.
In fact, if I recall correctly, the author of the driver recommends that it be used device-device rather than the more common usage of turning a file into a device.
Somewhere in this thread someone posted that the large offset was to the **second** FAT, it isn't, its the offset to the **first** FAT.
You can see that in the layout of the eMMC device itself, which has a DOS disk label in the first sector and a 32Mbyte offset to the start of the first partition's file system.
And yes, you can have a "DOS disk label" at the first sector of each partition, further dividing that partition.
Its in the MS specs. (please don't ask for the link, I lost it years ago).
But when you find it, you will find that it is a recursive definition.
Not many disk partitioning and formating applications handle that aspect of the "DOS disk label".
Back in the day that I needed it for a commercial project, I had to write my own.
