ipv4: Handle route deletion notification

When a route is deleted we potentially need to promote the next route in
the FIB alias list (e.g., with an higher metric). In case we find such a
route, a replace notification is emitted. Otherwise, a delete
notification for the deleted route.

v2:
* Convert to use fib_find_alias() instead of fib_find_first_alias()
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_trie.c

@@ -1570,6 +1570,36 @@ static void fib_remove_alias(struct trie *t, struct key_vector *tp,
 	node_pull_suffix(tp, fa->fa_slen);
 }
 
+static void fib_notify_alias_delete(struct net *net, u32 key,
+				    struct hlist_head *fah,
+				    struct fib_alias *fa_to_delete,
+				    struct netlink_ext_ack *extack)
+{
+	struct fib_alias *fa_next, *fa_to_notify;
+	u32 tb_id = fa_to_delete->tb_id;
+	u8 slen = fa_to_delete->fa_slen;
+	enum fib_event_type fib_event;
+
+	/* Do not notify if we do not care about the route. */
+	if (fib_find_alias(fah, slen, 0, 0, tb_id, true) != fa_to_delete)
+		return;
+
+	/* Determine if the route should be replaced by the next route in the
+	 * list.
+	 */
+	fa_next = hlist_entry_safe(fa_to_delete->fa_list.next,
+				   struct fib_alias, fa_list);
+	if (fa_next && fa_next->fa_slen == slen && fa_next->tb_id == tb_id) {
+		fib_event = FIB_EVENT_ENTRY_REPLACE_TMP;
+		fa_to_notify = fa_next;
+	} else {
+		fib_event = FIB_EVENT_ENTRY_DEL_TMP;
+		fa_to_notify = fa_to_delete;
+	}
+	call_fib_entry_notifiers(net, fib_event, key, KEYLENGTH - slen,
+				 fa_to_notify, extack);
+}
+
 /* Caller must hold RTNL. */
 int fib_table_delete(struct net *net, struct fib_table *tb,
 		     struct fib_config *cfg, struct netlink_ext_ack *extack)
@@ -1623,6 +1653,7 @@ int fib_table_delete(struct net *net, struct fib_table *tb,
 	if (!fa_to_delete)
 		return -ESRCH;
 
+	fib_notify_alias_delete(net, key, &l->leaf, fa_to_delete, extack);
 	call_fib_entry_notifiers(net, FIB_EVENT_ENTRY_DEL, key, plen,
 				 fa_to_delete, extack);
 	rtmsg_fib(RTM_DELROUTE, htonl(key), fa_to_delete, plen, tb->tb_id,