Re: [PATCH] man/man3/getnameinfo.3: Mention behavior for AF_UNIX

[Alejandro Colomar <alx@kernel.org>]

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Hi Jan,

> Date: 2026-10-20 13:51:43+0200
> From: Jan Engelhardt <jengelh@inai.de>
>
> Signed-off-by: Jan Engelhardt <jengelh@inai.de>
> ---
>  man/man3/getnameinfo.3 | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/man/man3/getnameinfo.3 b/man/man3/getnameinfo.3
> index 7db812948..6c2a08275 100644
> --- a/man/man3/getnameinfo.3
> +++ b/man/man3/getnameinfo.3
> @@ -121,6 +121,14 @@ cannot be determined.)
>  If set, then the numeric form of the service address is returned.
>  (When not set, this will still happen in case the service's name
>  cannot be determined.)
> +.P
> +Behavior for passing other sockaddr types to getnameinfo is unspecified by

This 'other' seems out of context.  I don't see a recent earlier mention
that the address family of the socket should be AF_INET/6.  There's one
at the top, but that seems far enough that a reader might get confused.

Perhaps we could have this text in a VERSIONS section, and instead of
assuming the reader remembers, we could be explicit about it.

> +POSIX.
> +Portable programs should not expect any particular behavior.
> +For e.g. AF_UNIX/sockaddr_un,
> +many libc implementations fail such a call,
> +some succeed but provide zero-length strings in \fIhost\fP and \fIserv\fP,
> +and some fill these buffers with pseudo values.

I'd rewrite a little bit:

	.SH VERSIONS
	POSIX only specifies the behavior for sockets of the
	.B AF_INET
	and
	.B AF_INET6
	address families.
	Other address families are non-portable;
	for example, for
	.BR AF_UNIX ,
	many libc implementations fail,
	some succeed but provide zero-length strings in
	.I host
	and
	.IR serv ,
	and some fill these buffers with pseudo-values.

BTW, out of curiosity, what do those pseudo-values look like?


Have a lovely day!
Alex

>  .SS Extensions to getnameinfo() for Internationalized Domain Names
>  Starting with glibc 2.3.4,
>  .BR getnameinfo ()
> -- 
> 2.56.0
> 
> 

-- 
<https://www.alejandro-colomar.es>

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