netdev - Re: [PATCH net-next 4/4] net/sched: act_mirred: Implement ingress actions

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Date:   Tue, 27 Sep 2016 17:18:04 +0300
From:   Shmulik Ladkani <shmulik.ladkani@...ellosystems.com>
To:     David Miller <davem@...emloft.net>, daniel@...earbox.net
Cc:     jhs@...atatu.com, xiyou.wangcong@...il.com, edumazet@...gle.com,
        netdev@...r.kernel.org, shmulik.ladkani@...il.com
Subject: Re: [PATCH net-next 4/4] net/sched: act_mirred: Implement ingress
 actions

On Tue, 27 Sep 2016 09:44:41 -0400 (EDT), davem@...emloft.net wrote:
> From: Daniel Borkmann <daniel@...earbox.net>
> Date: Tue, 27 Sep 2016 12:39:34 +0200
> 
> > Any reason why dev_forward_skb() is not preferred over direct
> > netif_receive_skb() you're using? It would, for example, implicitly
> > assure that pkt_type is always PACKET_HOST, etc.
> 
> dev_forward_skb() will pull the ethernet header.
> 
> And since a direct call to netif_receive_skb() will not, one of these
> two choices won't work properly.

In the patch, I'm issuing a skb_pull_rcsum() prior the netif_receive_skb,
snip:

+	/* If action's target direction differs than filter's direction,
+	 * and devices expect a mac header on xmit, then mac push/pull is
+	 * needed.
+	 */
+	if (at != tcf_mirred_act_direction(m->tcfm_eaction) &&
+	    m->tcfm_mac_header_xmit) {
+		if (at & AT_EGRESS) {
+			/* caught at egress, act ingress: pull mac */
+			mac_len = skb_network_header(skb) - skb_mac_header(skb);
+			skb_pull_rcsum(skb2, mac_len);

Existing *egress* mir/red already supported pairing two non-eth devices.
Therefore I allow it for the new *ingress* mir/red as well.

Now, following this premise, the skb_pull_rcsum() shown above is executed
for devices whose xmit is mac_header based.

I've tested both ARPHRD_ETHER devices and some non ARPHRD_ETHER devices.

(an *existing* symmetric skb_push_rcsum() is invoked if packet is caught at
 ingress and redirected for egress on a mac_header xmit device)

This was the reason for picking netif_receive_skb() over dev_forward_skb().

Regards,
Shmulik