Date: Sun, 4 Dec 2011 08:49:08 -0800 From: mdf@FreeBSD.org To: John Baldwin <jhb@freebsd.org> Cc: Zack Kirsch <zack@freebsd.org>, freebsd-arch@freebsd.org Subject: Re: Use of bool / stdbool.h in kernel Message-ID: <CAMBSHm9R8zLYNoewhK11zc_v-w2E-euETD0_b=-FUozZ1rD_3w@mail.gmail.com> In-Reply-To: <201111301032.04102.jhb@freebsd.org> References: <CAMBSHm_Be0hCimgg0KpCFs24MHOW=LBczJbFZ3F1cOaCgrS8LA@mail.gmail.com> <20111130154604.B949@besplex.bde.org> <201111301032.04102.jhb@freebsd.org>
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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. =A0This 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>? =A0That is, is the >> >> Would be a larger style bug, especially if it were actually used. >> Even its spellings of TRUE and FALSE are strange. =A0Even 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. =A0src/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. :) =A0I don't th= ink > that means we have to forgo use of the new type now that it is in fact > standardized in C99. =A0I 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). *sigh*, part of the problem is the buggy way in which C99 added the bool type. I suppose code could always use the real reserved keyword _Bool in headers, ugly though it is, and bool in implementation files. I had a brief look, and for comparison Linux has the typedef in linux/include/types.h IIRC but does not guard the definition nor did it define true/false. Thanks, matthew
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