netdev - Re: [PATCH v3 net-next 4/4] net/sched: act

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Date:   Fri, 07 Oct 2016 04:38:19 +0900
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Shmulik Ladkani <shmulik.ladkani@...il.com>,
        David Miller <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 net-next 4/4] net/sched: act_mirred: Implement
 ingress actions

On Thu, 2016-10-06 at 10:30 -0700, Cong Wang wrote:
> On Thu, Oct 6, 2016 at 6:30 AM, Shmulik Ladkani
> <shmulik.ladkani@...il.com> wrote:
> > Hi,
> >
> > On Mon, Oct 3, 2016 at 12:45 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> >> On Thu, Sep 29, 2016 at 4:03 AM, Shmulik Ladkani
> >> <shmulik.ladkani@...il.com> wrote:
> >>>         skb2->skb_iif = skb->dev->ifindex;
> >>>         skb2->dev = dev;
> >>> -       err = dev_queue_xmit(skb2);
> >>> +       if (tcf_mirred_act_direction(m_eaction) & AT_EGRESS)
> >>> +               err = dev_queue_xmit(skb2);
> >>> +       else
> >>> +               netif_receive_skb(skb2);
> >>
> >> Any reason why not check the return value here?
> >
> > Rationale: netif_receive_skb returns err if there was no protocol
> > handler to deliver the skb to.
> > If skb is not caught by any protocol handler, this should not be
> > considered an "ingress redirect" error. The redirect action should be
> > considered successful.
> 
> A quick grep shows there are many places returning NET_RX_DROP:
> E.g.

And another quick grep shows that out of 142 drivers, only one [1] of
them (incorrectly) checks netif_receive_skb() return value.

Real question is more like : what is the impact of propagating an error
at this point ?

[1] drivers/net/caif/caif_virtio.c 
This is incorrect because at the driver layer, the packet was received
and the rx_packets/rx_bytes counters _should_ be incremented regardless
of packet being dropped or not by upper layers.