Re: sfc: an enumeration is not a bitmask

Michał Mirosław
2011-05-17T23:19:22Z

W dniu 18 maja 2011 00:00 użytkownik Jeff Garzik <jgarzik@pobox.com> napisał:
> On 05/17/2011 03:09 PM, Michał Mirosław wrote:
>> 2011/5/17 Jeff Garzik<jgarzik@pobox.com>:
>>> 2011/5/17 David Miller<davem@davemloft.net>:
>>>> An enumeration is not a bitmask, instead it means one out of the set
>>>> of enumerated values will be used.
>>> It's a decade-old kernel practice to use 'enum' to define typed
>>> constants, preferred over  macros that convey no type information and
>>> disappear after cpp phase.
>>>
>>> So your assertion about enumerations is demonstrably not true, as it
>>> is often used in the kernel.  Call it enum abuse if you want, but it
>>> is consistent with code all over the kernel.
>> Old age of the mistake doesn't make it correct.
> It is not a mistake, but a useful coding tool.

Being it a mistake does not contradict usefulness. ;-)

C has bitfields for the uses where masks and shifts are usually used.
Unfortunately, those usually require more typing and sometimes compile
to worse code.

Best Regards,
Michał Mirosław