Re: [PATCH] grantpt.3: explicitly mention #define _XOPEN_SOURCE requirement

Emanuele Torre
2024-05-26T16:58:41Z

On Sun, May 26, 2024 at 06:38:35PM +0200, Alejandro Colomar wrote:
> Hi Emanuele,
>
> On Sun, May 26, 2024 at 05:11:58PM GMT, Emanuele Torre wrote:
> > > On Sun, May 26, 2024 at 04:19:30PM GMT, Emanuele Torre wrote:
> > > > I've just noticed that ptsname.3 is also missing #define _XOPEN_SOURCE
> > > > in its synopsis; however #define _XOPEN_SOURCE does not seem to work.
> > > Did you define it to 500, or an empty value?
> >
> > empty value.
>
> Hmm.
>
> > > You need to define it to an appropriate value. (The synopsis is a bit
> > > misleading, and we could/should specify the minimum value.)
> >
> > I did notice the
> >
> > ptsname():
> > Since glibc 2.24:
> > _XOPEN_SOURCE >= 500
> > glibc 2.23 and earlier:
> > _XOPEN_SOURCE
> >
> > But that is the same text that appears in grantpt.3 and unlockpt.3, and
> > they get included with just _XOPEN_SOURCE.
> >
> > I also noticed it this morning when I sent my patch for grantpt.3, but I
> > ignored it assuming I probably misunderstood its meaning since it worked
> > with just _XOPEN_SOURCE.
>
> I also noticed and ignored it, since I saw the same text in the other
> pages.

Yes, I copied the line from unlockpt.3 after seeing it there, and seeing
it resolved the issue.

>
> > Does this mean that my grantpt.3 patch is wrong?
> >
> > And that #define _XOPEN_SOURCE in the synopsys of unlockpt.3 is also
> > wrong?
>
> Regardless of it being correct or not, I think using the definition
> used by newer glibc versions is better, so we could update the SYNOPSIS
> of all pages to show the requirements of the latest glibc.
>
> > I should not use just #define _XOPEN_SOURCE without a value in my
> > programs if I want to use ptsname(3), grantpt(3), unlockpt(3)?
>
> TBH, I don't know. AFAICS, _XOPEN_SOURCE without specifying a value
> means POSIX.1‐1990 (maybe? not sure). That is so obsolete these days
> that I don't know what it means. Does it provide ptsname(3)? I don't
> know. But yeah, I'd say just don't use it.
>
> These days, POSIX.1-2001 is granted everywhere (except maybe some dying
> proprietary systems), and even POSIX.1-2008 if you restrict yourself to
> Linux and the BSDs. I suggest using the flags that enable one of these
> more recent standards.

Yes, I guess when necessary it's probably easier to just always use
#define _GNU_SOURCE instead of messing with _XOPEN_SOURCE,
_POSIX_C_SOURCE, etc.

o/
emanuele6