On Wed, Jan 26, 2022 at 10:18 AM David Ahern <dsahern@xxxxxxxxx> wrote:
>
> On 1/24/22 6:15 AM, menglong8.dong@xxxxxxxxx wrote:
> > diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
> > index ab9bee4bbf0a..77bb9ddc441b 100644
> > --- a/net/ipv4/ip_input.c
> > +++ b/net/ipv4/ip_input.c
> > @@ -318,8 +318,10 @@ static int ip_rcv_finish_core(struct net *net, struct sock *sk,
> > {
> > const struct iphdr *iph = ip_hdr(skb);
> > int (*edemux)(struct sk_buff *skb);
> > + int err, drop_reason;
> > struct rtable *rt;
> > - int err;
> > +
> > + drop_reason = SKB_DROP_REASON_NOT_SPECIFIED;
> >
> > if (ip_can_use_hint(skb, iph, hint)) {
> > err = ip_route_use_hint(skb, iph->daddr, iph->saddr, iph->tos,
> > @@ -339,8 +341,10 @@ static int ip_rcv_finish_core(struct net *net, struct sock *sk,
> > if (ipprot && (edemux = READ_ONCE(ipprot->early_demux))) {
> > err = INDIRECT_CALL_2(edemux, tcp_v4_early_demux,
> > udp_v4_early_demux, skb);
> > - if (unlikely(err))
> > + if (unlikely(err)) {
> > + drop_reason = SKB_DROP_REASON_EARLY_DEMUX;
>
> is there really value in this one? You ignore the error case from
> ip_route_use_hint which is a similar, highly unlikely error path so why
> care about this one? The only failure case is ip_mc_validate_source from
> udp_v4_early_demux and 'early demux' drops really mean nothing to the user.
>
Ok, let's just ignore it ( In fact, it's because that I don't know
what 'early demux'
do :/ )
>
> > goto drop_error;
> > + }
> > /* must reload iph, skb->head might have changed */
> > iph = ip_hdr(skb);
> > }
> > @@ -353,8 +357,10 @@ static int ip_rcv_finish_core(struct net *net, struct sock *sk,
> > if (!skb_valid_dst(skb)) {
> > err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
> > iph->tos, dev);
> > - if (unlikely(err))
> > + if (unlikely(err)) {
> > + drop_reason = SKB_DROP_REASON_IP_ROUTE_INPUT;
>
> The reason codes should be meaningful to users and not derived from a
> code path. What does SKB_DROP_REASON_IP_ROUTE_INPUT mean as a failure?
>
Is't it meaningful? I name it from the meaning of 'ip route lookup or validate
failed in input path', can't it express this information?
>
> > goto drop_error;
> > + }
> > }
> >
> > #ifdef CONFIG_IP_ROUTE_CLASSID
