From:   Patrick Steinhardt <ps@pks.im>
To:     linux-nfs@vger.kernel.org
Cc:     Patrick Steinhardt <ps@pks.im>
Subject: [PATCH 1/3] configure.ac: more carefully detect availability of res_querydomain(3)
Date:   Mon,  4 Feb 2019 15:31:18 +0100
Message-Id: <a6f2aaea93c1293e62d5109b10d47a7675a45393.1549290423.git.ps@pks.im>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk

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>
---
 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@:>@])])
-- 
2.20.1