Re: [PATCH] net/ipv4/*, net/core/neighbour.c jiffies cleanup

[David S. Miller]

   From: Andreas Dilger <[e-mail]>
   Date: Wed, 7 Nov 2001 17:36:27 -0700

   No, only a limited number of them cast to a signed value, which means
   that a large number of them get the comparison wrong in the case of
   jiffies wrap (where the difference is a large unsigned value, and not
   a small negative number).
   
Why do they these cases that are actually in the code need to cast to
a signed value to get a correct answer?  They are not like your
example.

Almost all of these cases are:

	(jiffies - SOME_VALUE_KNOWN_TO_BE_IN_THE_PAST) > 5 * HZ

So you say if we don't cast to signed, this won't get it right on
wrap-around?  I disagree, let's say "long" is 32-bits and jiffies
wrapped around to "0x2" and SOME_VALUE... is 0xfffffff8.  The
subtraction above yields 10, and that is what we want.

Please show me a bad case where casting to signed is necessary.

I actually ran through the tree the other night myself starting to
convert these things, then I noticed that I couldn't even convince
myself that the code was incorrect.

Franks a lot,
David S. Miller
[e-mail]