Re: [PATCH] memmem.3: Added list of known systems where this is available

[Stefan Puiu <stefan.puiu@gmail.com>]

Hi,

On Wed, Nov 23, 2022 at 3:16 PM Alejandro Colomar
<alx.manpages@gmail.com> wrote:
>
> Hi all!
>
[... snipped ...]
> >
> > Not sure if it's the job of Linux man-pages to document when other
> > OSes started supporting certain APIs. That info has to be maintained,
> > updated etc. People can always read the man pages of other systems,
> > right? Maybe it's worth only pointing out when an interface is
> > Linux-only, or the Linux implementation diverges significantly.
>
> The good thing is that in most cases, it's either something in POSIX (for which
> I gon't care at all if Apple Libc or another-weirdo-libc decide to not support
> it), or it's a Linux-only function.
>
> So, there are few functions or syscalls that are generally available but are not
> in POSIX, and it might be interesting to document that they're effectively as
> portable as anything POSIX.  Maybe even POSIX editors read this and decide to
> add it.
>
> In those cases, we still need to decide what we care about or not.

Aah OK, so memmem is non-standard, there is no standard to point to.
Do other OSes provide this kind of info? I don't see anything about
portability in the OpenBSD man page (https://man.openbsd.org/memmem),
only "memmem() is a GNU extension". The FreeBSD man page
(https://www.freebsd.org/cgi/man.cgi?query=memmem&manpath=FreeBSD+13.1-RELEASE+and+Ports)
does mention Linux, but only to mention that memmem was broken in old
versions of Linux libc (nothing about current Linux); it also has the
'GNU extension' mention. Interestingly, I don't see the mention of the
function being a GNU extension in the Linux version.

Have you checked, are there many such functions? Do you plan to add
this info for all of them?

>
> Musl libc is definitely a first-class citizen these days in Linux distributions.
>   I would start documenting them in the project at large if someone from musl
> provides patches (I discussed this some time ago, but can't remember with who).
> Rich, if you would like to discuss about this, we can have some chat.
>
> >
> > For musl and other libcs, I think the man pages already document some
> > instances where their behavior diverges from glibc.
>
> As said, for musl, I'd document them officially, if there's anyone interested
> enough to send patches.
>
> For other libcs, we have to decide if they're important enough, and probably
> decide on a case-by-case basis.
>
> Michael tried to have some decent coverage of non-GNU/Linux systems, both in the
> man-pages and in his TLPI book.  It's a useful thing.  So much that sometimes
> you don't even need to read other systems' pages at all to know how portable is
> a GNU/Linux function.

I know. But not sure how much Linux docs should cover about other
OSes, which are also constantly changing (and have their own fine
docs).

As always, just my 2c,
Stefan.

>
> So, I'd like to get opinions on interest about documenting details about:
>
> - newlib (I never heard about it before; is it a widespread thing? do you think
> it's useful?)
> - Apple Libc (I still don't like it, but I must admit that it's relevant, and
> being open source, it's more palatable)
> - bionic (does anyone know if that's useful at all for anyone at all?)
>
> Support for those wouldn't go as far as musl or glibc.  For now it would only be
> for memmem(3).
>
>
> Cheers,
>
> Alex
>
> --
> <http://www.alejandro-colomar.es/>