On Fri, Nov 09, 2018 at 01:41:35PM +0100, Kamil Rytarowski wrote: > >> > I wanna do this, looks good? > >> > >> It should probably use double wings: > >> > >> > -#ifndef int8_t > >> > +#ifndef _BSD_INT8_T_ > >> > >> +#ifndef __BSD_INT8_T__ > > > > In terms of namespace consumption, the single leading underscore > > followed by an uppercase letter as used here is sufficient. > > We alredy use this syntax, eg. in <sys/timespec.h>: > > #ifdef _BSD_TIME_T_ > typedef _BSD_TIME_T_ time_t; > #undef _BSD_TIME_T_ > #endif > > (however here the ifdef is switched for some reason)
Those are older, and work differently. So looking the same isn't necessarily a feature. all of it ought to be retconned. The basic problem is: according to standards, certain typedefs need to be exposed by any of several headers but not others; and some typedefs need to be accessible to headers that are not allowed to expose them. (Crazy as that sounds.) However, any combination or order of #includes must generate only one typedef as repeated typedefs anger the compiler. To make life more exciting, some of these types are also machine-dependent and most of them need to be shared between userland and kernel. The "correct" way to handle this (as in, the worked-out and tested way based on twenty years of hindsight and having seen and tried various other less successful ways) is: (1) Create an exported kernel header, that is not part of any user-facing API and that will never be, and put all the affected MI types in it as typedefs with underscore prefixes (like __time_t). This header file should define nothing outside of the implementation namespace so it can be included freely anywhere. (2) Create an exported MD kernel header, ditto, and put all the MD types in it similarly, one for every port and/or one for every machine. This header file can also be included freely anywhere. (3) In all headers subject to namespace restrictions, which includes most stuff shared between user and kernel, write the header itself using only the underscore-prefix types. This makes these headers compilable using only the private exported headers (1) and (2). (4) For every group of types with a different set of exposure criteria (there are not so many of these actually) create a header file, that is not part of any user-facing API and will never be, that has a conventional cpp guard against multiple inclusion, and put the typedefs for the non-underscore prefixes of the types in the group in this header. Include this header in each userland header that is supposed to expose this group of types, and also in sys/types.h, which is allowed/supposed to expose everything. This covers all the standards requirements, minimizes the amount of cutpaste, and avoids having unexpected #defines floating around breaking builds. The only drawback is that it requires a place to put header files that are not part of user-facing APIs, and in particular such a place that can be shared user/kernel. We don't currently have such a place in NetBSD. It also is best used together with a kernel headers setup where shared user/kernel headers are clearly separated from kernel internal headers, to minimize the number of places where extra leading underscores are needed and to keep it clear where those are. We also don't have this in NetBSD. This in turn should be fixed, and I have been threatening for years to fix it once we get rename support in version control ... and maybe we're finally getting near the point where tha'ts possible. -- David A. Holland dholl...@netbsd.org
