console:/ $ losetup --help
usage: losetup [-cdrs] [-o OFFSET] [-S SIZE] {-d DEVICE...|-j FILE|-af|{DEVICE FILE}}

Associate a loopback device with a file, or show current file (if any)
associated with a loop device.

Instead of a device:
-a      Iterate through all loopback devices
-f      Find first unused loop device (may create one)
-j FILE Iterate through all loopback devices associated with FILE

existing:
-c      Check capacity (file size changed)
-d DEV  Detach loopback device
-D      Detach all loopback devices

new:
-s      Show device name (alias --show)
-o OFF  Start association at offset OFF into FILE
-r      Read only
-S SIZE Limit SIZE of loopback association (alias --sizelimit)