Alexander Duyck <alexander.du...@gmail.com> wrote:
There isn't any need to add such an indication, nor do we need to start bitflipping the return value from csum_fold in all cases. I think there was just some confusion about UDP checksums vs GRE or TCP checksums.
Yeah. I think I finally got there. The naive software methods will never generate a true 0 unless everything was zero. Real one's complement machines did addition in terms of subtraction so that 1 + -1 would never produce a -0, only a normal 0. Of course a simple adder would produce a -0, making it impossible to get back to a normal 0.
I'd say we are better off keeping this simple. The original patch just needs to drop the check for the resultant checksum being 0 since that is not needed for GRE.
I'm all in favor of simple. I had just started to worry about a possible change in behavior that might have interoperability problems with some implementations. I wonder if any implementation ever did the addition by subtraction, but also failed to make 0 compare equal to -0? I guess if they knew enough to do the former, they should not have blown the latter.
-- Mark Rustad, Networking Division, Intel Corporation
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