How to undo all changes in a buffer made since it was open in Vim?

Question

How can I undo all changes since opening a buffer? I imagine there may be some form of :earlier that does this.

Update: Many are suggesting

Answer 1

To access previously saved file status, I think the following work :

:earlier 1f

From the documentation :

 :earlier {N}f      Go to older text state {N} file writes before.
                When changes were made since the last write
                ":earlier 1f" will revert the text to the state when
                it was written.  Otherwise it will go to the write
                before that.
                When at the state of the first file write, or when
                the file was not written, ":earlier 1f" will go to
                before the first change.