What does "loop" mean in "loop device"?
This maybe a linguistic question. I have checked the loop device on Wikipedia. It is just for mounting files as block device. But what does "loop" mean here? Its usage here is totally bizarre to me. I am not a native English speaker. So could someone explain this jargon to me in plain English? :)
It's short for "loopback".
The concept is also known as a disk image. I guess because driver calls to the image get passed along to the underlying driver of the physical disk. There is no actual loop involved; it is an additional level to a driver stack which is already several layers deep.
(I've written an encrypted disk image driver, and I find the "loopback" terminology incorrect and confusing.)
I guess this term comes from the communication realm when sometimes it is needed to test the communication system by simulating a peer using a proxy circuit loop.
The concept came also to UNIX networking where loopback network interfaces do not send network traffic to the medium.
The same concept in file systems loop means that the file system driver does not really goes through the hard disk IO stack and, instead, ends using a plain disk image file for IO.