FM / loop

/sys/devices/virtual/block/loop12/loop

Name	Size	Mode	Actions
autoclear	4096	0444	edit dl rm
backing_file	4096	0444	edit dl rm
dio	4096	0444	edit dl rm
offset	4096	0444	edit dl rm
partscan	4096	0444	edit dl rm
sizelimit	4096	0444	edit dl rm

Edit: /sys/devices/virtual/block/loop12/loop/offset (4096B)