ipv4: Consolidate all default route selection implementations.

Both fib_trie and fib_hash have a local implementation of
fib_table_select_default().  This is completely unnecessary
code duplication.

Since we now remember the fib_table and the head of the fib
alias list of the default route, we can implement one single
generic version of this routine.

Looking at the fib_hash implementation you may get the impression
that it's possible for there to be multiple top-level routes in
the table for the default route.  The truth is, it isn't, the
insert code will only allow one entry to exist in the zero
prefix hash table, because all keys evaluate to zero and all
keys in a hash table must be unique.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 56 insertions, 0 deletions

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 1bf6fb906cfc..b15857d2b77e 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1136,6 +1136,62 @@ int fib_sync_down_dev(struct net_device *dev, int force)
         return ret;
 }
 
+/* Must be invoked inside of an RCU protected region.  */
+void fib_select_default(struct fib_result *res)
+{
+        struct fib_info *fi = NULL, *last_resort = NULL;
+        struct list_head *fa_head = res->fa_head;
+        struct fib_table *tb = res->table;
+        int order = -1, last_idx = -1;
+        struct fib_alias *fa;
+
+        list_for_each_entry_rcu(fa, fa_head, fa_list) {
+                struct fib_info *next_fi = fa->fa_info;
+
+                if (fa->fa_scope != res->scope ||
+                    fa->fa_type != RTN_UNICAST)
+                        continue;
+
+                if (next_fi->fib_priority > res->fi->fib_priority)
+                        break;
+                if (!next_fi->fib_nh[0].nh_gw ||
+                    next_fi->fib_nh[0].nh_scope != RT_SCOPE_LINK)
+                        continue;
+
+                fib_alias_accessed(fa);
+
+                if (fi == NULL) {
+                        if (next_fi != res->fi)
+                                break;
+                } else if (!fib_detect_death(fi, order, &last_resort,
+                                             &last_idx, tb->tb_default)) {
+                        fib_result_assign(res, fi);
+                        tb->tb_default = order;
+                        goto out;
+                }
+                fi = next_fi;
+                order++;
+        }
+
+        if (order <= 0 || fi == NULL) {
+                tb->tb_default = -1;
+                goto out;
+        }
+
+        if (!fib_detect_death(fi, order, &last_resort, &last_idx,
+                                tb->tb_default)) {
+                fib_result_assign(res, fi);
+                tb->tb_default = order;
+                goto out;
+        }
+
+        if (last_idx >= 0)
+                fib_result_assign(res, last_resort);
+        tb->tb_default = last_idx;
+out:
+        rcu_read_unlock();
+}
+
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 
 /*