loopback on block device

[Lei Yang]

Hello,

Here is a question for loopback device. As far as I understand,  the 
loopback device is used to mount files as if they were block devices.

Then Why I could do "losetup -e XOR /dev/loop0 /dev/ram0" ? Notice that 
ram0 is not mounted anywhere and does not have a filesystem on it. I've 
tried that command and there seems to be no error. I got confused and 
looked into loop.c, it seems to me that a loopback device should be 
associated with a "backing file", why would it work on a block device 
anyway?

I'd appreciate your comments greatly!

TIA,
Lei

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