Disk usage != File apparent size

[josephpaul0]

The term "disk usage", as in UNIX du command, means space really occupied on the filesystem, not the apparent file size.
For an example of a program written in golang that displays disk usage, you can look at the source code of tdu: https://bitbucket.org/josephpaul0/tdu

[missedone]

The term "disk usage", as in UNIX du command, means space really occupied on the filesystem, not the apparent file size.

you're correct.