netdev - Re: netif_receive_skb return value in bridging scenario

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Date:	Tue, 26 Feb 2013 08:35:28 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Bercaru Cristian-B43982 <B43982@...escale.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: netif_receive_skb return value in bridging scenario

On Tue, 2013-02-26 at 14:57 +0000, Bercaru Cristian-B43982 wrote:
> Hello!
> 
> I noticed that the return value of __netif_receive_skb is initialized
> to NET_RX_DROP.
> 
> If the bridging code handles the packet and successfully returns
> RX_HANDLER_CONSUMED, __netif_receive_skb returns the default value,
> NET_RX_DROP. I don't think it is fair to consider the packet dropped,
> since it is received successfully.
> 
> I thought the return value of __netif_receive_skb was used by Ethernet
> NIC drivers for updating their RX_DROP and RX_OX counters, but I
> studied the source code of various drivers and they seem to ignore
> whatever the return value. It seems strange. Then shouldn't the
> function header look like      " void netif_receive_skb(... "  ?

It seems better to factorize whatever is needed in core network layer,
instead of adding code in all drivers to check netif_receive_skb()
return code.

Check the follwing "atomic_long_inc(&skb->dev->rx_dropped);"
in __netif_receive_skb_core()

For the case you mention, I guess we need the following patch 

diff --git a/net/core/dev.c b/net/core/dev.c
index 17bc535..e98fb4d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3446,6 +3446,7 @@ ncls:
 		}
 		switch (rx_handler(&skb)) {
 		case RX_HANDLER_CONSUMED:
+			ret = NET_RX_SUCCESS;
 			goto unlock;
 		case RX_HANDLER_ANOTHER:
 			goto another_round;


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