dm-verity setup on loop device

Dear,

While trying to understand the dm-verity code, I tried making a small
verity setup. I created 1 readonly loop device and 1 non-readonly loop
device. When I then try to create the verity target with the readonly
as data device (not using veritysetup because I want to experiment on
a low level), dmesg still says that the device is not in readonly
mode.

Is it possible what I'm trying to achieve?
If so, what am I doing wrong?

Thanks! Regards Jasper