Re: [PATCH] net: compare_ether_addr[_64bits]() has no ordering

On Mon, 2012-05-07 at 19:20 -0400, David Miller wrote:

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Neither compare_ether_addr() nor compare_ether_addr_64bits()
(as it can fall back to the former) have comparison semantics
like memcmp() where the sign of the return value indicates sort
order. We had a bug in the wireless code due to a blind memcmp
replacement because of this.

A cursory look suggests that the wireless bug was the only one
due to this semantic difference.

Signed-off-by: Johannes Berg <redacted>
---
 include/linux/etherdevice.h |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

The right way to avoid this kind of problems is to change these
functions to return a bool

Well, I guess so, but that'd be a weird thing for a compare_ function...
should probably be named equal_... then, but I'm not really able to do
such a huge change on the first day after my vacation :-)

It's true the name could be improved, but changing the name is quite
a large undertaking even with automated scripts.

Even the bool change is slightly painful, since all of the explicit
tests against integers (%99.999 of these are in wireless BTW :-) would
need to be adjusted.

I suppose I could fix those first and then later change the type, but I
think having a "compare_ether_addr" function that returns *false* when
they *match* would be rather confusing. I'd rather have
"equal_ether_addr()" that returns *true* when they match.

I guess we could introduce equal_ether_addr() though and slowly convert,
keeping compare_ether_addr() as a sort of wrapper around it.

johannes