[PATCH] babel: Log the reason when refusing to run on an interface

[Toke Høiland-Jørgensen]

The babel protocol code checks various properties of an interface before
starting it: whether the interface is up, whether it supports multicast,
and whether it has a link-local address assigned. However, it doesn't give
any feedback if any of those checks fail, it just silently ignores the
interface.

Fix this by explicitly logging errors when any of the checks fail; to avoid
spamming the logs for all interfaces on the system, move the checks so they
are only performed after it was determined that an interface is actually
configured by an interface pattern.

Reported-by: Stefan Haller <stefan.haller at stha.de>
Signed-off-by: Toke Høiland-Jørgensen <toke at toke.dk>
---
 proto/babel/babel.c | 50 ++++++++++++++++++++++++---------------------
 1 file changed, 27 insertions(+), 23 deletions(-)

diff --git a/proto/babel/babel.c b/proto/babel/babel.c
index 4b6b9d7f9f6f..6ac3bb6a7fec 100644
--- a/proto/babel/babel.c
+++ b/proto/babel/babel.c
@@ -1639,6 +1639,29 @@ babel_remove_iface(struct babel_proto *p, struct babel_iface *ifa)
   rfree(ifa->pool); /* contains ifa itself, locks, socket, etc */
 }
 
+static int iface_is_valid(struct babel_proto *p, struct iface *iface)
+{
+  if (!(iface->flags & IF_UP)) {
+    log(L_ERR "%s: Interface '%s' is down", p->p.name, iface->name);
+    return 0;
+  }
+
+  if (!(iface->flags & IF_MULTICAST)) {
+    log(L_ERR "%s: Interface '%s' does not support multicast",
+        p->p.name, iface->name);
+    return 0;
+  }
+
+  /* We need a link-local address to communicate */
+  if (!iface->llv6) {
+    log(L_ERR "%s: Interface '%s' has no link-local address assigned",
+        p->p.name, iface->name);
+    return 0;
+  }
+
+  return 1;
+}
+
 static void
 babel_if_notify(struct proto *P, unsigned flags, struct iface *iface)
 {
@@ -1655,19 +1678,8 @@ babel_if_notify(struct proto *P, unsigned flags, struct iface *iface)
     if (ifa)
       babel_remove_iface(p, ifa);
 
-    if (!(iface->flags & IF_UP))
-      return;
-
-    /* We only speak multicast */
-    if (!(iface->flags & IF_MULTICAST))
-      return;
-
-    /* Ignore ifaces without link-local address */
-    if (!iface->llv6)
-      return;
-
     struct babel_iface_config *ic = (void *) iface_patt_find(&cf->iface_list, iface, NULL);
-    if (ic)
+    if (ic && iface_is_valid(p, iface))
       babel_add_iface(p, iface, ic);
 
     return;
@@ -1733,20 +1745,12 @@ babel_reconfigure_ifaces(struct babel_proto *p, struct babel_config *cf)
 
   WALK_LIST(iface, iface_list)
   {
-    if (!(iface->flags & IF_UP))
-      continue;
-
-    /* Ignore non-multicast ifaces */
-    if (!(iface->flags & IF_MULTICAST))
-      continue;
-
-    /* Ignore ifaces without link-local address */
-    if (!iface->llv6)
-      continue;
-
     struct babel_iface *ifa = babel_find_iface(p, iface);
     struct babel_iface_config *ic = (void *) iface_patt_find(&cf->iface_list, iface, NULL);
 
+    if (ic && !iface_is_valid(p, iface))
+      continue;
+
     if (ifa && ic)
     {
       if (babel_reconfigure_iface(p, ifa, ic))
-- 
2.31.1