Re: [PATCH net-next] ipv4/fib: send RTM_DELROUTE notify when flush fib

[Hangbin Liu <liuhangbin@gmail.com>]

On Tue, Jul 18, 2023 at 08:58:14AM -0700, Stephen Hemminger wrote:
> On Tue, 18 Jul 2023 13:19:06 +0300
> Ido Schimmel <idosch@idosch.org> wrote:
> 
> > fib_table_flush() isn't only called when an address is deleted, but also
> > when an interface is deleted or put down. The lack of notification in
> > these cases is deliberate. Commit 7c6bb7d2faaf ("net/ipv6: Add knob to
> > skip DELROUTE message on device down") introduced a sysctl to make IPv6
> > behave like IPv4 in this regard, but this patch breaks it.
> > 
> > IMO, the number of routes being flushed because a preferred source
> > address is deleted is significantly lower compared to interface down /
> > deletion, so generating notifications in this case is probably OK. It

How about ignore route deletion for link down? e.g.

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 74d403dbd2b4..11c0f325e887 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -2026,6 +2026,7 @@ void fib_table_flush_external(struct fib_table *tb)
 int fib_table_flush(struct net *net, struct fib_table *tb, bool flush_all)
 {
        struct trie *t = (struct trie *)tb->tb_data;
+       struct nl_info info = { .nl_net = net };
        struct key_vector *pn = t->kv;
        unsigned long cindex = 1;
        struct hlist_node *tmp;
@@ -2088,6 +2089,11 @@ int fib_table_flush(struct net *net, struct fib_table *tb, bool flush_all)

                        fib_notify_alias_delete(net, n->key, &n->leaf, fa,
                                                NULL);
+                       if (!(fi->fib_flags & RTNH_F_LINKDOWN)) {
+                               rtmsg_fib(RTM_DELROUTE, htonl(n->key), fa,
+                                         KEYLENGTH - fa->fa_slen, tb->tb_id, &info, 0);
+                       }
                        hlist_del_rcu(&fa->fa_list);
                        fib_release_info(fa->fa_info);
                        alias_free_mem_rcu(fa);

> > also seems to be consistent with IPv6 given that rt6_remove_prefsrc()
> > calls fib6_clean_all() and not fib6_clean_all_skip_notify().
> 
> Agree. Imagine the case of 3 million routes and device goes down.
> There is a reason IPv4 behaves the way it does.