See debian discussions in
That same hash.h is also part of fio, and the original commit there has a Signed-off-by line:
Also Debian themselves say that it is GPL-2+ (and copyrighted by William Lee Irwin III):
> It was [pointed out] by one of our license group that [hash.h] is the
> same that has a GPL-2+ in [fio] which has a signed-off-by.
> [pointed out]
Yes, the Signed-off-by is from Jens Axboe (in CC) but he's not the
original author, I guess he just copied the file as Arnaldo did. The
file he committed has not any reference to the license.
I'm afraid that this entry in wrong. I'll seek confirmation with Martin Steigerwald.