Steve, All, On 2016-08-15 11:16 -0400, Steve Dickson spake thusly: > On 08/15/2016 10:23 AM, Chuck Lever wrote: > >> On Aug 14, 2016, at 6:13 PM, Yann E. MORIN <yann.morin.1998@xxxxxxx> wrote: > >> On 2016-08-14 14:30 -0400, Chuck Lever spake thusly: > >>>> On Aug 13, 2016, at 10:05 AM, Yann E. MORIN <yann.morin.1998@xxxxxxx> wrote: > >>>> > >>>> The __P() macro is defined in cdefs.h, so we must include it explicitly > >>>> rather than relying on it being included by another header. > >>>> > >>>> cdefs.h is a glibc-ism; glibc includes it almost everywhere from its own > >>>> headers. So it automatically gets included for glibc. > >>>> > >>>> However, cdefs.h is not present in musl, so its headers do not include > >>>> it. We must thus include it when we need __P() (of course, one will have > >>>> to provide his own cdefs.h in this case). > >>> > >>> Simply adding "#include <sys/cdefs.h>" seems like the wrong approach. > >>> If cdefs.h is not guaranteed to exist, the appropriate thing to do > >>> is provide some autoconf machinery to define __P() in its absence. > >> > >> OpenEmbedded provides comaptibility headers: > >> http://git.openembedded.org/openembedded-core/tree/meta/recipes-core/bsd-headers/bsd-headers > >> > >> In Buildroot, we're adding them too (not yet applied, WIP): > >> http://lists.busybox.net/pipermail/buildroot/2016-August/169722.html > >> > >> Other embedded buildsystem may each have their own fix in a way or > >> another... > >> > >> Mainstream distros are more-or-less all based on glibc, except for a few > >> outliers, like Alpine Linux (also based on musl), and they've gone on > >> the "remove __P()" route: > >> http://git.alpinelinux.org/cgit/aports/tree/main/rpcbind/0001-Avoid-use-of-glibc-sys-cdefs.h-header.patch > >> > >>> On the other hand, I wonder if we need to continue to preserve K&R C > >>> compatibility in this code base. Perhaps instead the uses of __P() > >>> should be eliminated? > >> > >> I tried to provide a minimalist approach, that consists in assuming that > >> cdefs.h is present. > > > > If cdefs.h presence cannot be guaranteed (and I think you've adequately > > demonstrated that no guarantee exists), at the very least there needs > > to be some autoconf logic to handle the "cdefs.h is not present" case. > > IMO a strictly minimalist approach won't work here. > I don't see how it *can't* exist... At lease with Fedora and RHEL > cdefs.h is part of the glibc-headers rpm and without that nothing > in nfs-utils is going to compile Well, not everything is using glibc; there are other C libraries in the world. Not everything is Fedora or RHEL either; there are other distros out there. Not everything is a distro either; there are embedded systems that use custom buildsystems. musl is a strict standard-compliant C library; it does not implement anything not in a standard. sys/cdefs.h is defined in no standard, thus not provided by musl. http://www.musl-libc.org/ Furthermore, nothing in nfs-utils uses sys/cdefs.h or the usual culprit macros defined in there: $ git grep -E 'cdefs\.h|__P|_DECLS' [nothing] For the record, in Buildroot we do build nfs-utils on musl without any issue. > >> But I do agree that pre-ANSI compatibility is probably a little tiny > >> wee bit excessive nowadays. Virtually all current compilers do accept > >> function prototypes, nowadays... > >> > >> I can work on a patch that does just get rid of the use of __P(). (we > >> can't really vampirise the patch from Alpine, as there's no SoB or such > >> origin information on it; not that redoing the patch would be too > >> difficult either...). > >> > >> So, what route, now? ;-) > > > > My preference as a reviewer and individual contributor: > > > > Barring any further comments here, provide two different approaches: > > > > 1. add autoconf logic to detect when sys/cdefs.h is not available, > > and provide a substitute __P() macro. That might be as simple as > > defining __P in a local auto.m4 script when it is not provided by > > system headers. > I thinking we should fail the configuration if sys/cdefs.h does not > exist... And thus break on systems that do not use glibc (or uClibc)? > > 2. remove invocations of the __P() macro from the rpcbind source > Any idea what could break by removing them?? Virtually nothing. If you look at the glibc code, __P(arg) just expands to its argument arg: /* These two macros are not used in glibc anymore. They are kept here only because some other projects expect the macros to be defined. */ #define __P(args) args #define __PMT(args) args Note that Chuck and I are talking about removing the use of the __P() macro, not about removing the prototypes. E.g., transform such code: int f __P((inti )); into: int f(int i); which is what happens anyway with the __P() macro. > > Post both to the mailing lists and folks here can decide which is > > better. > > > > You might not have time for all that ;-) so you could pick one and > > add a strong technical argument in the patch description why that > > is the best choice. > > > > I think I like 2. overall as it should leave the rpcbind source > > code a little easier to read, no new autoconf logic is needed, and > > there appears to be one distro that is already going that way. > I lean more toward taking the patch as is and failing the > configuration if the header file does not exist.. Still the case with the above explanations? Regards, Yann E. MORIN. -- .-----------------.--------------------.------------------.--------------------. | Yann E. MORIN | Real-Time Embedded | /"\ ASCII RIBBON | Erics' conspiracy: | | +33 662 376 056 | Software Designer | \ / CAMPAIGN | ___ | | +33 223 225 172 `------------.-------: X AGAINST | \e/ There is no | | http://ymorin.is-a-geek.org/ | _/*\_ | / \ HTML MAIL | v conspiracy. | '------------------------------^-------^------------------^--------------------' -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
