Re: Removing sys/sysmacros.h from sys/types.h

[Rich Felker <dalias@libc.org>]

On Sat, Jun 29, 2019 at 02:00:46PM -0700, Michael Forney wrote:
> On 2019-06-14, Rich Felker <dalias@libc.org> wrote:
> > On Fri, Jun 14, 2019 at 01:20:21PM -0700, Benjamin Wright wrote:
> >> Hello,
> >>
> >> Would it be possible to remove the sys/sysmacros.h include from
> >> sys/types.h?
> >>
> >> This change was added in 2011 -
> >> https://git.musl-libc.org/cgit/musl/commit/include/sys/types.h?id=f552c792c7ce5a560f214e1104d93ee5b0833967
> >>
> >> However it appears to have been removed from other standard libc
> >> implementations around ~2015 based on this announcement:
> >> https://sourceware.org/ml/libc-alpha/2015-11/msg00253.html
> >>
> >> This can cause issues with user defined symbol collision of the symbols
> >> major, minor or makedev.
> >
> > Yes, I'd actually forgotten we did this. I'll remove it right away in
> > time for the next release.
> 
> I'm just curious if there is a good way to use these macros in
> software that is otherwise portable without adding a configure script.
> Most BSDs don't have sys/sysmacros.h, and now glibc and musl require
> including sys/sysmacros.h to use them.
> 
> It's a shame that while these macros are available on most unix-like
> operating systems, they can't be accessed in a generic way.

There's really not much of a use for them at all in portable software.
Devices having "major/minor numbers", rather than dev_t just being an
abstract identifier, is an anachronism that's not really compatible
with exploding numbers of device types or operating systems that don't
expose any idea of a type/major.

If you really do need them, you should probably just search for them
with a configure check, first for sys/sysmacros.h, then for any other
historical places they might have been found in.

Rich