Work around libnl address caching bug

rtnl_addr requires that all addresses have the "peer" attribute set in
order to be compared for equality, but this attribute is not normally
set. As a result, most addresses will not compare as equal even to
themselves, busting caching. We fix this for now by poking into the
guts of libnl if it is broken...

configure.ac

@@ -208,6 +208,7 @@ AC_SUBST(UDEV_BASE_DIR)
 PKG_CHECK_MODULES(LIBNL, libnl-1 >= 1.0-pre8)
 AC_SUBST(LIBNL_CFLAGS)
 AC_SUBST(LIBNL_LIBS)
+NM_LIBNL_CHECK
 
 PKG_CHECK_MODULES(UUID, uuid)
 AC_SUBST(UUID_CFLAGS)

m4/libnl-check.m4

@@ -0,0 +1,65 @@
+AC_DEFUN([NM_LIBNL_CHECK], [
+    AC_MSG_CHECKING([for libnl address caching bug])
+    save_CFLAGS="$CFLAGS"
+    save_LDFLAGS="$LDFLAGS"
+    CFLAGS="$CFLAGS $LIBNL_CFLAGS"
+    LDFLAGS="$LDFLAGS $LIBNL_LIBS"
+    AC_RUN_IFELSE([
+#include <stdio.h>
+#include <netlink/route/addr.h>
+#include <netlink/object-api.h>
+
+int
+main (int argc, char **argv)
+{
+	struct nl_handle *nlh;
+	struct nl_cache *cache;
+	struct nl_object *obj;
+
+	nlh = nl_handle_alloc ();
+	if (nl_connect (nlh, NETLINK_ROUTE) < 0) {
+		fprintf (stderr, "couldn't connect to netlink: %s", nl_geterror ());
+		return 3;
+	}
+
+	cache = rtnl_addr_alloc_cache (nlh);
+	if (!cache || nl_cache_nitems (cache) == 0) {
+		fprintf (stderr, "couldn't fill address cache: %s", nl_geterror ());
+		return 3;
+	}
+
+	obj = nl_cache_get_first (cache);
+	if (nl_object_identical (obj, obj))
+		return 0;
+
+	nl_cache_get_ops (cache)->co_obj_ops->oo_id_attrs &= ~0x80;
+	if (nl_object_identical (obj, obj))
+		return 1;
+	else
+		return 2;
+}
+], libnl_bug=$?, libnl_bug=$?, libnl_bug=cross)
+
+    CFLAGS="$save_CFLAGS"
+    LDFLAGS="$save_LDFLAGS"
+
+    case $libnl_bug in
+    0) AC_MSG_RESULT([no])
+       ;;
+
+    1) AC_MSG_RESULT([yes, using workaround])
+       AC_DEFINE(LIBNL_NEEDS_ADDR_CACHING_WORKAROUND, 1, [Define this to hack around buggy libnl rtnl_addr caching])
+       ;;
+
+    2) AC_MSG_RESULT([yes, and workaround doesn't work])
+       AC_MSG_ERROR([Installed libnl has broken address caching; please patch or upgrade])
+       ;;
+
+    cross) AC_MSG_RESULT([cross-compiling... assuming it works!])
+           ;;
+
+    *) AC_MSG_RESULT([?])
+       AC_MSG_ERROR([libnl test program failed])
+       ;;
+esac
+])

src/nm-netlink.c

@@ -18,6 +18,8 @@
  * Copyright (C) 2007 - 2008 Red Hat, Inc.
  */
 
+#include "config.h"
+
 #include "nm-netlink.h"
 #include "nm-utils.h"
 
@@ -25,6 +27,7 @@
 #include <signal.h>
 #include <pthread.h>
 #include <unistd.h>
+#include <netlink/object-api.h>
 
 static struct nl_cache * link_cache = NULL;
 static struct nl_handle * def_nl_handle = NULL;
@@ -58,6 +61,9 @@ struct nl_handle *
 nm_netlink_get_default_handle (void)
 {
 	struct nl_cb *cb;
+#ifdef LIBNL_NEEDS_ADDR_CACHING_WORKAROUND
+	struct nl_cache *addr_cache;
+#endif
 
 	if (def_nl_handle)
 		return def_nl_handle;
@@ -74,6 +80,18 @@ nm_netlink_get_default_handle (void)
 		return NULL;
 	}
 
+#ifdef LIBNL_NEEDS_ADDR_CACHING_WORKAROUND
+	/* Work around apparent libnl bug; rtnl_addr requires that all
+	 * addresses have the "peer" attribute set in order to be compared
+	 * for equality, but this attribute is not normally set. As a
+	 * result, most addresses will not compare as equal even to
+	 * themselves, busting caching.
+	 */
+	addr_cache = rtnl_addr_alloc_cache (def_nl_handle);
+	nl_cache_get_ops (addr_cache)->co_obj_ops->oo_id_attrs &= ~0x80;
+	nl_cache_free (addr_cache);
+#endif
+
 	return def_nl_handle;
 }