TIL: Loop Devices

When you run mount files.sqfs some_dir there’s quite a bit that goes on behind the curtain. Using strace it’s pretty clear what happens. The mount utility actually creates a “loop” device first, then mounts that device to some_dir. A loop device is way to take a file on disk and make it available as a mountable device.

I learned this while trying to figure out how to mount SquashFS files within our Firecracker sandbox using Go.