[libvirt] [PATCHv2] build: force libnl1 if netcf also used libnl1

[Eric Blake]

Recent spec file changes ensure that in distro situations, netcf
and libvirt will link against the same libnl in order to avoid
dumping core.  But for every-day development, if you are F17 and
have the libnl3-devel headers available, libvirt was blindly
linking against libnl3 even though F17 netcf still links against
libnl1, making testing a self-built binary on F17 impossible.

By making configure a little bit smarter, we can avoid this
situation - we merely skip the probe of libnl-3 if we can prove
that netcf is still using libnl-1.  I intentionally wrote the
test so that we still favor libnl-3 if netcf is not installed or
if we couldn't use ldd to determine things.

Defaults being what they are, someone will invariably complain
that our smarts were wrong.  Never fear - in that case, just run
./configure LIBNL_CFLAGS=..., where the fact that you set
LIBNL_CFLAGS (even to the empty string) will go back to probing
for libnl-3, regardless of netcf's choice.

* configure.ac (LIBNL): Don't probe libnl3 if netcf doesn't use it.
---

v2: check for libnetcf.so, in usual suspect locations; and document
a way to override things if the guess is wrong.

 configure.ac | 34 +++++++++++++++++++++++++---------
 1 file changed, 25 insertions(+), 9 deletions(-)

diff --git a/configure.ac b/configure.ac
index 47a72b9..6a96bf3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2902,14 +2902,30 @@ LIBNL_LIBS=""
 have_libnl=no

 if test "$with_linux" = "yes"; then
-    PKG_CHECK_MODULES([LIBNL], [libnl-3.0], [
-        have_libnl=yes
-        AC_DEFINE([HAVE_LIBNL3], [1], [Use libnl-3.0])
-        AC_DEFINE([HAVE_LIBNL], [1], [whether the netlink library is available])
-        PKG_CHECK_MODULES([LIBNL_ROUTE3], [libnl-route-3.0])
-        LIBNL_CFLAGS="$LIBNL_CFLAGS $LIBNL_ROUTE3_CFLAGS"
-        LIBNL_LIBS="$LIBNL_LIBS $LIBNL_ROUTE3_LIBS"
-    ], [PKG_CHECK_MODULES([LIBNL], [libnl-1 >= $LIBNL_REQUIRED], [
+    # When linking with netcf, we must ensure that we pick the same version
+    # of libnl that netcf picked.  Prefer libnl-3 unless we can prove
+    # netcf linked against libnl-1, or unless the user set LIBNL_CFLAGS.
+    libnl_ldd=
+    for dir in /usr/lib64 /usr/lib; do
+        if test -f $dir/libnetcf.so; then
+            libnl_ldd=`(ldd $dir/libnetcf.so) 2>&1`
+            break
+        fi
+    done
+    case $libnl_ldd:${LIBNL_CFLAGS+set} in
+        *libnl.so.1*:) ;;
+        *)
+        PKG_CHECK_MODULES([LIBNL], [libnl-3.0], [
+            have_libnl=yes
+            AC_DEFINE([HAVE_LIBNL3], [1], [Use libnl-3.0])
+            AC_DEFINE([HAVE_LIBNL], [1], [whether the netlink library is available])
+            PKG_CHECK_MODULES([LIBNL_ROUTE3], [libnl-route-3.0])
+            LIBNL_CFLAGS="$LIBNL_CFLAGS $LIBNL_ROUTE3_CFLAGS"
+            LIBNL_LIBS="$LIBNL_LIBS $LIBNL_ROUTE3_LIBS"
+        ], []) ;;
+    esac
+    if test "$have_libnl" = no; then
+        PKG_CHECK_MODULES([LIBNL], [libnl-1 >= $LIBNL_REQUIRED], [
             have_libnl=yes
             AC_DEFINE_UNQUOTED([HAVE_LIBNL], [1],
              [whether the netlink library is available])
@@ -2920,7 +2936,7 @@ if test "$with_linux" = "yes"; then
                 AC_MSG_ERROR([libnl-devel >= $LIBNL_REQUIRED is required for macvtap support])
             fi
         ])
-    ])
+    fi
 fi
 AM_CONDITIONAL([HAVE_LIBNL], [test "$have_libnl" = "yes"])

-- 
1.7.11.4