On Thu, 10 Feb 2022 11:19:49 +0800 Menglong Dong wrote: > I'm doing the job of using kfree_skb_reason() for the TCP layer, > and I have some puzzles. > > When collecting drop reason for tcp_v4_inbound_md5_hash() in > tcp_v4_rcv(), I come up with 2 ways: > > First way: pass the address of reason to tcp_v4_inbound_md5_hash() > like this: > > static bool tcp_v4_inbound_md5_hash(const struct sock *sk, > const struct sk_buff *skb, > - int dif, int sdif) > + int dif, int sdif, > + enum skb_drop_reason *reason) > > This can work, but many functions like tcp_v4_inbound_md5_hash() > need to do such a change. > > Second way: introduce a 'drop_reason' field to 'struct sk_buff'. Therefore, > drop reason can be set by 'skb->drop_reason = SKB_DROP_REASON_XXX' > anywhere. > > For TCP, there are many cases where you can't get a drop reason in > the place where skb is freed, so I think there needs to be a way to > deeply collect drop reasons. The second can resolve this problem > easily, but extra fields may have performance problems. > > Do you have some better ideas? On a quick look tcp_v4_inbound_md5_hash() returns a drop / no drop decision, so you could just change the return type to enum skb_drop_reason. SKB_DROP_REASON_NOT_SPECIFIED is 0 is false, so if (reason) goto drop; logic will hold up.
