Use of bool / stdbool.h in kernel
John Baldwin
jhb at freebsd.org
Thu Dec 1 15:12:18 UTC 2011
On Wednesday, November 30, 2011 8:49:44 pm David Schultz wrote:
> On Wed, Nov 30, 2011, John Baldwin wrote:
> > On Wednesday, November 30, 2011 12:13:53 am Bruce Evans wrote:
> > > On Tue, 29 Nov 2011 mdf at freebsd.org wrote:
> > >
> > > > At $WORK we have a hack in one of the *.mk files to allow including
> > > > stdbool.h in the kernel and we use it extensively. This is not
> > > > allowed by style(9), as far as I can tell, because the file is in
> > > > include/stdbool.h and those files are not allowed to be included in
> > > > kernel sources.
> > >
> > > Including stdbool.h in the kernel is not a style bug, but unsupported.
> > >
> > > > What I want to check on is, would it be acceptable to move stdbool.h
> > > > from include/stdbool.h to sys/sys/stdbool.h (i.e. like errno.h) and
> > > > then include it in the kernel as <sys/stdbool.h>? That is, is the
> > >
> > > Would be a larger style bug, especially if it were actually used.
> > > Even its spellings of TRUE and FALSE are strange. Even in userland
> > > stdbool.h is considered so useful that it is never used in src/bin
> > > and is only used a few times on other src/*bin. src/bin never uses
> > > TRUE of FALSE either.
> >
> > I suspect there is some bias here though due to the fact that there wasn't
> > a standard bool type when most of this code was written. :) I don't think
> > that means we have to forgo use of the new type now that it is in fact
> > standardized in C99. I would be happy to have 'bool' available and the
> > lowercase 'true' and 'false' are fine with me.
>
> The lowercase 'true' and 'false' are intended to mimic C++, where
> they are keywords. Regardless of how you prefer to capitalize
> them, using them instead of 0 and 1 makes the intent much clearer.
> This is especially true in the kernel, where non-zero could mean
> true, or it could be an error code.
>
> Unfortunately, the "new type" is mostly useless, aside from
> improving readability. Unlike modern languages, C doesn't
> consider it a compile-time error to mix up bools and ints.
Yes, I consider it a readability aide and think it is fine as such.
--
John Baldwin
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