Date: Tue, 05 Mar 2013 13:06:45 +0100 From: Hans Petter Selasky <hps@bitfrost.no> To: Bruce Evans <brde@optusnet.com.au> Cc: Davide Italiano <davide@FreeBSD.org>, src-committers@FreeBSD.org, John Baldwin <jhb@FreeBSD.org>, attilio@FreeBSD.org, Gleb Smirnoff <glebius@FreeBSD.org>, svn-src-projects@FreeBSD.org Subject: Re: svn commit: r247710 - projects/calloutng/sys/kern Message-ID: <5135DFD5.5050708@bitfrost.no> In-Reply-To: <20130305214655.C1224@besplex.bde.org> References: <201303031339.r23DdsBU047737@svn.freebsd.org> <201303041521.06557.jhb@freebsd.org> <CAJ-FndBvLD_fU1ZZ3cGNtChfdtXyuBRt4Z_ci8daS08ZYdOKzg@mail.gmail.com> <201303041620.52100.jhb@freebsd.org> <20130305201211.M902@besplex.bde.org> <20130305094819.GI48089@FreeBSD.org> <20130305214655.C1224@besplex.bde.org>
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On 03/05/13 12:21, Bruce Evans wrote:
> On Tue, 5 Mar 2013, Gleb Smirnoff wrote:
>
>> On Tue, Mar 05, 2013 at 08:43:33PM +1100, Bruce Evans wrote:
>> B> > I think for new code we should prefer C99's bool to boolean_t.
>> B>
>> B> Why? There is no existing practice for this in the kernel. There
>> is some
>> B> in the Linux kernel :-).
>>
>> Why? Because it is standard. What for? To make it more easy for newcomers
>> to start hacking on FreeBSD kernel.
>
> I think you mean "harder". Now the newcomers need to know:
> - the old method, which is used in most places
> - the new method
> - style rules for old, new and mixed methods
> - arcane C99 points like whether bool can be used in bit-fields (I had to
> look this up to check it. It can).
>
> I now see technical reasons to never use bool in kernel or other low-level
> code. It will cause minor pessimizations converting nonzero to true (1)
> at runtime, and for converting bool to register_t when passing parameters
> (bool is 1 byte on x86). To use bool in structs (when not packing it into
> bit-fields), we need to know too much about its size to pack it properly...
>
> Bruce
Hi,
I'm not sure how good you all are at C99. There is a subtle difference
between bool (compiler type) and boolean_t (typedef'ed), and that is
when assigning an non-bool value. This is probably bad style, but I just
want to show you the difference:
#include <stdbool.h>
#include <stdio.h>
typedef int boolean_t;
int main()
{
bool var1;
var1 = 3;
printf("%d\n", var1);
boolean_t var2;
var2 = 3;
printf("%d\n", var2);
return (0);
}
If defined correctly, var1 should contain a value of "1", and var2
should contain a value of "3". Now if for some reason someone like
possibly some Linux guys do, use booleans for counting, you will have an
instant error :-) I'm not saying we should take their example, but
anyhow, be warned about the difference between bool and boolean_t!
--HPS
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