Subject: Re: [PATCH 1/3] configure.ac: more carefully detect availability of
 res_querydomain(3)
To:     Patrick Steinhardt <ps@pks.im>, linux-nfs@vger.kernel.org
References: <a6f2aaea93c1293e62d5109b10d47a7675a45393.1549290423.git.ps@pks.im>
From:   Steve Dickson <SteveD@RedHat.com>
Message-ID: <01523a34-5c3b-383a-a532-cb9bc0f4af8f@RedHat.com>
Date:   Wed, 27 Feb 2019 12:14:16 -0500
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On 2/4/19 9:31 AM, Patrick Steinhardt wrote:
> Since glibc 2.2, the function res_querydomain(3) is implemented as a
> define to `__res_querydomain`. Due to this implementation detail, using
> `AC_CHECK_LIB` with a symbol name of "res_querydomain" will cause a
> linking failure and thus fail to detect its availability. This is why
> right now, we try to detect availability of `__res_querydomain` instead.
> 
> Unfortunately, this may break on other platforms where there is no
> `__res_querydomain` but only the function without leading underscores.
> To fix this, we can perform another `AC_CHECK_LIB([resolv],
> [res_querydomain], ...)` call in case where the other one was not found
> and only raise an error if both symbols weren't found.
> 
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
Committed...

steved.
> ---
>  configure.ac | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/configure.ac b/configure.ac
> index 4bf5aea..cb9d921 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -411,7 +411,8 @@ if test "$enable_gss" = yes; then
>  fi
>  
>  dnl libdnsidmap specific checks
> -AC_CHECK_LIB([resolv], [__res_querydomain], , AC_MSG_ERROR(res_querydomain needed))
> +AC_CHECK_LIB([resolv], [__res_querydomain], ,
> +	AC_CHECK_LIB([resolv], [res_querydomain], , AC_MSG_ERROR(res_querydomain needed)))
>  
>  AC_ARG_ENABLE([ldap],
>  	[AS_HELP_STRING([--disable-ldap],[Disable support for LDAP @<:default=detect@:>@])])
>