Date: Tue, 9 Sep 2014 11:33:33 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: yaneurabeya@gmail.com Cc: "freebsd-arch@FreeBSD.org Arch" <freebsd-arch@freebsd.org> Subject: Re: [RFC] Add __arraycount from NetBSD to sys/cdefs.h Message-ID: <20140909083333.GA2737@kib.kiev.ua> In-Reply-To: <146C3E96-7461-4D30-8B7F-5E20F72CF061@gmail.com> References: <CAGHfRMBMPra5YXDn0e83dpVxwnarg3DL8o31xr7DhWv%2BVXskTg@mail.gmail.com> <8D279BDC-7D40-4750-8DA7-A4535DD2E458@bsdimp.com> <146C3E96-7461-4D30-8B7F-5E20F72CF061@gmail.com>
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On Mon, Sep 08, 2014 at 09:29:54AM -0700, yaneurabeya@gmail.com wrote:
> On Sep 3, 2014, at 21:17, Warner Losh <imp@bsdimp.com> wrote:
>=20
> > On Sep 3, 2014, at 9:45 PM, Garrett Cooper <yaneurabeya@gmail.com> wrot=
e:
> >=20
> >> Hi all,
> >> In order to ease porting code and reduce divergence with NetBSD
> >> when importing code (a large chunk of which for me are tests), I would
> >> like to move nitems to sys/cdefs.h and alias __arraycount to nitems.
> >> Here's the __arraycount #define in lib/libnetbsd/sys/cdefs.h:
> >>=20
> >> 44 /*
> >> 45 * Return the number of elements in a statically-allocated array,
> >> 46 * __x.
> >> 47 */
> >> 48 #define __arraycount(__x) (sizeof(__x) / sizeof(__x[0]))
> >>=20
> >> Here's the nitems #define in sys/sys/param.h:
> >>=20
> >> 277 #define nitems(x) (sizeof((x)) / sizeof((x)[0]))
> >>=20
> >> sys/cdefs.h gets pulled in automatically with sys/param.h, so
> >> anything using nitems will continue to function like before (see below
> >> for more details). I've attached a patch which addresses all hardcoded
> >> definitions in the tree added by FreeBSD developers.
> >> If there aren't any major concerns with my proposed change, I'll
> >> put it up for review on Phabricator.
> >> Thank you!
> >> -Garrett
> >>=20
> >> $ cat cdefs_pound_define.c
> >> #include <sys/param.h>
> >>=20
> >> #ifdef _SYS_CDEFS_H_
> >> #warning "sys/cdefs.h has been included"
> >> #endif
> >> $ cc -c cdefs_pound_define.c
> >> cdefs_pound_define.c:4:2: warning: "sys/cdefs.h has been included" [-W=
#warnings]
> >> #warning "sys/cdefs.h has been included"
> >> ^
> >> 1 warning generated.
> >> $ cc -D_KERNEL -c cdefs_pound_define.c
> >> cdefs_pound_define.c:4:2: warning: "sys/cdefs.h has been included" [-W=
#warnings]
> >> #warning "sys/cdefs.h has been included"
> >> ^
> >> 1 warning generated.
> >> $ gcc -c cdefs_pound_define.c
> >> cdefs_pound_define.c:4:2: warning: #warning "sys/cdefs.h has been incl=
uded"
> >> $ gcc -D_KERNEL -c cdefs_pound_define.c
> >> cdefs_pound_define.c:4:2: warning: #warning "sys/cdefs.h has been incl=
uded?
> >=20
> > I wouldn?t bother changing the nitems #define. There?s no need, really,=
to do that.
>=20
> Rethinking my proposal, I agree. I had lofty hopes for unifying the macro=
s, but the functional duplication (1 line) is harmless.
>=20
> > I?d also be more inclined to believe the test if you tested what the th=
ing does rather than test for an artificial, implementation defined side ef=
fect.
>=20
> Sure. I provided a lazy proof instead of a full proof :).
>=20
> > But honestly the amount of duplication saved here is rather tiny?
>=20
> Indeed! Thank you for the input :) ? I?ve attached a new patch which does=
n?t disturb nitems or sys/param.h.
Since this is seriously discussed on arch@, I think it is worth look
at the following:
git grep -e 'sizeof.*/sizeof' -- | grep -v '^contrib' | grep '#.*define' | =
wc -l
118
These are only defines, not uses, not counting direct use of
sizeof(x)/sizeof(x[0]) in the code.
Not all of them are for equiv macros, but significant part repeats ntimes()
in variations. At least Linuxish ARRAY_SIZE/DRM_ARRAY_SIZE is much more
popular than __arraysize() which appears three (!) times.
I do not see any reason to pollute central header cdefs.h with sparcely
used macro for some compat code.
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