Re: [PATCH net-next v3 2/3] net: icmp: introduce __ping_queue_rcv_skb() to report drop reasons

[Paolo Abeni <pabeni@redhat.com>]

On Thu, 2022-03-17 at 13:25 +0800, Menglong Dong wrote:
> On Thu, Mar 17, 2022 at 11:56 AM David Ahern <dsahern@kernel.org> wrote:
> > 
> > On 3/16/22 12:31 AM, menglong8.dong@gmail.com wrote:
> > > diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
> > > index 3ee947557b88..9a1ea6c263f8 100644
> > > --- a/net/ipv4/ping.c
> > > +++ b/net/ipv4/ping.c
> > > @@ -934,16 +934,24 @@ int ping_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock,
> > >  }
> > >  EXPORT_SYMBOL_GPL(ping_recvmsg);
> > > 
> > > -int ping_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
> > > +static enum skb_drop_reason __ping_queue_rcv_skb(struct sock *sk,
> > > +                                              struct sk_buff *skb)
> > >  {
> > > +     enum skb_drop_reason reason;
> > > +
> > >       pr_debug("ping_queue_rcv_skb(sk=%p,sk->num=%d,skb=%p)\n",
> > >                inet_sk(sk), inet_sk(sk)->inet_num, skb);
> > > -     if (sock_queue_rcv_skb(sk, skb) < 0) {
> > > -             kfree_skb(skb);
> > > +     if (sock_queue_rcv_skb_reason(sk, skb, &reason) < 0) {
> > > +             kfree_skb_reason(skb, reason);
> > >               pr_debug("ping_queue_rcv_skb -> failed\n");
> > > -             return -1;
> > > +             return reason;
> > >       }
> > > -     return 0;
> > > +     return SKB_NOT_DROPPED_YET;
> > > +}
> > > +
> > > +int ping_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
> > > +{
> > > +     return __ping_queue_rcv_skb(sk, skb) ?: -1;
> > >  }
> > >  EXPORT_SYMBOL_GPL(ping_queue_rcv_skb);
> > > 
> > 
> > This is a generic proto callback and you are now changing its return
> > code in a way that seems to conflict with existing semantics
> 
> The return value of ping_queue_rcv_skb() seems not changed.
> In the previous code, -1 is returned on failure and 0 for success.
> This logic isn't changed, giving __ping_queue_rcv_skb() != 0 means
> failure and -1 is returned. Isn't it?

With this patch, on failure __ping_queue_rcv_skb() returns 'reason' (>
0) and ping_queue_rcv_skb() returns the same value.

On success __ping_queue_rcv_skb() returns SKB_NOT_DROPPED_YET (==0) and
ping_queue_rcv_skb() return -1.

You need to preserve the old ping_queue_rcv_skb() return values, under
the same circumstances.

Thanks,

Paolo