Date: Tue, 6 Dec 2011 12:27:15 -0500 From: John Baldwin <jhb@freebsd.org> To: mdf@freebsd.org Cc: Zack Kirsch <zack@freebsd.org>, freebsd-arch@freebsd.org Subject: Re: Use of bool / stdbool.h in kernel Message-ID: <201112061227.15438.jhb@freebsd.org> In-Reply-To: <CAMBSHm9R8zLYNoewhK11zc_v-w2E-euETD0_b=-FUozZ1rD_3w@mail.gmail.com> References: <CAMBSHm_Be0hCimgg0KpCFs24MHOW=LBczJbFZ3F1cOaCgrS8LA@mail.gmail.com> <201111301032.04102.jhb@freebsd.org> <CAMBSHm9R8zLYNoewhK11zc_v-w2E-euETD0_b=-FUozZ1rD_3w@mail.gmail.com>
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On Sunday, December 04, 2011 11:49:08 am mdf@freebsd.org wrote: > On Wed, Nov 30, 2011 at 7:32 AM, John Baldwin <jhb@freebsd.org> wrote: > > On Wednesday, November 30, 2011 12:13:53 am Bruce Evans wrote: > >> On Tue, 29 Nov 2011 mdf@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. > > In further thinking, there's also a style issue of nested headers. > FreeBSD expects most types defined in sys/types.h so that it can be > included first and other files alphabetically. Using <sys/stdbool.h> > would require any header with a bool parameter, return code, or struct > member to include <sys/stdbool.h>. Alternatively, I could instead put > the same guards as stdbool.h uses and define bool, true, and false in > sys/types.h, but only for _KERNEL use (however, this also would create > issues with any file that is built in both user-space and kernel, and > unconditionally defining in sys/types.h could break existing buggy > applications). Userland apps that #define _KERNEL deserve to be broken and deal with the fallout accordingly. :) I think exposing it in the kernel via <sys/types.h> would be fine. -- John Baldwin
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