[PATCH] sysconf: Add _SC_NSIG

[Adhemerval Zanella Netto]

On 24/01/25 13:28, Tavian Barnes wrote:
> POSIX.1-2024 introduces a portable way to get the highest possible
> signal number (plus one): sysconf(_SC_NSIG).  This is equivalent to
> glibc's non-portable NSIG macro.
> 
> Link: https://www.austingroupbugs.net/view.php?id=741
> Signed-off-by: Tavian Barnes <tavianator@tavianator.com>

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> 
> ---
> 
> There is also a new NSIG_MAX constant, but I'm less sure how to expose
> that.  That is supposed to be the highest possible signal number (plus
> one) that sigset_t could support, so that new signals can be added
> without breaking ABI.  If that's not a concern, we could just do
> 
>     #define NSIG_MAX NSIG
> 
> Otherwise, it would have to be something like
> 
>     #define NSIG_MAX (CHAR_BIT * sizeof(sigset_t) + 1)
> 
> but that's not usable in preprocessor conditionals.  (I'm not sure it
> has to be, but most of the *_MAX macros are I think.)

POSIX defines that NSIG_MAX should be a symbolic constant and this
should be suitable for use in #if preprocessing.  However, we already
do not follow it for some other constant, like MINSIGSTKSZ; due other
constraints.

Maybe we can do something like:

#define NSIG_MAX (CHAR_BIT * _SIGSET_NWORDS * __SIZEOF_LONG__ + 1)

And define _SIGSET_NWORDS for Hurd.  I think we can even define __SIZEOF_LONG__
based __WORDSIZE to avoid relying on the pre-processor.

> 
> ---
>  bits/confname.h         | 5 ++++-
>  posix/getconf.c         | 2 ++
>  posix/sysconf.c         | 2 ++
>  posix/tst-getconf.sh    | 1 +
>  sysdeps/posix/sysconf.c | 7 +++++++
>  5 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/bits/confname.h b/bits/confname.h
> index 2eaf8a2eb2..9084e3ac90 100644
> --- a/bits/confname.h
> +++ b/bits/confname.h
> @@ -531,8 +531,11 @@ enum
>      _SC_MINSIGSTKSZ,
>  #define	_SC_MINSIGSTKSZ			_SC_MINSIGSTKSZ
>  
> -    _SC_SIGSTKSZ
> +    _SC_SIGSTKSZ,
>  #define	_SC_SIGSTKSZ			_SC_SIGSTKSZ
> +
> +    _SC_NSIG
> +#define	_SC_NSIG			_SC_NSIG
>    };
>  
>  /* Values for the NAME argument to `confstr'.  */
> diff --git a/posix/getconf.c b/posix/getconf.c
> index 4ba9c0dee8..29933ceeb5 100644
> --- a/posix/getconf.c
> +++ b/posix/getconf.c
> @@ -405,6 +405,8 @@ static const struct conf vars[] =
>      { "_POSIX_IPV6", _SC_IPV6, SYSCONF },
>      { "_POSIX_RAW_SOCKETS", _SC_RAW_SOCKETS, SYSCONF },
>  
> +    { "NSIG", _SC_NSIG, SYSCONF },
> +
>      { NULL, 0, SYSCONF }
>    };
>  
> diff --git a/posix/sysconf.c b/posix/sysconf.c
> index c3bf3b78fa..0f93305fe9 100644
> --- a/posix/sysconf.c
> +++ b/posix/sysconf.c
> @@ -269,6 +269,8 @@ __sysconf (int name)
>      case _SC_MINSIGSTKSZ:
>      case _SC_SIGSTKSZ:
>  
> +    case _SC_NSIG:
> +
>        break;
>      }
>  
> diff --git a/posix/tst-getconf.sh b/posix/tst-getconf.sh
> index eeb4c51d84..30f442b83a 100644
> --- a/posix/tst-getconf.sh
> +++ b/posix/tst-getconf.sh
> @@ -56,6 +56,7 @@ _NPROCESSORS_CONF
>  NPROCESSORS_CONF
>  _NPROCESSORS_ONLN
>  NPROCESSORS_ONLN
> +NSIG
>  MQ_OPEN_MAX
>  MQ_PRIO_MAX
>  OPEN_MAX
> diff --git a/sysdeps/posix/sysconf.c b/sysdeps/posix/sysconf.c
> index 8f9a0adab2..853fd42a23 100644
> --- a/sysdeps/posix/sysconf.c
> +++ b/sysdeps/posix/sysconf.c
> @@ -1209,6 +1209,13 @@ __sysconf (int name)
>  #else
>        return -1;
>  #endif
> +
> +    case _SC_NSIG:
> +#ifdef NSIG
> +      return NSIG;
> +#else
> +      return -1;
> +#endif
>      }
>  }
>