netdev - Re: [patch net-next-2.6] net: vlan: make non-hw-accel rx path similar to hw-accel

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Message-ID: <20110403132228.GA2737@psychotron.redhat.com>
Date:	Sun, 3 Apr 2011 15:22:29 +0200
From:	Jiri Pirko <jpirko@...hat.com>
To:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
Cc:	Stephen Hemminger <shemminger@...ux-foundation.org>,
	netdev@...r.kernel.org, davem@...emloft.net, kaber@...sh.net,
	fubar@...ibm.com, eric.dumazet@...il.com, andy@...yhouse.net,
	xiaosuo@...il.com, jesse@...ira.com
Subject: Re: [patch net-next-2.6] net: vlan: make non-hw-accel rx path
 similar to hw-accel

Sun, Apr 03, 2011 at 11:27:29AM CEST, nicolas.2p.debian@...il.com wrote:
>Le 02/04/2011 20:27, Jiri Pirko a écrit :
>>Sat, Apr 02, 2011 at 05:55:24PM CEST, shemminger@...ux-foundation.org wrote:
>>>On Sat,  2 Apr 2011 12:26:06 +0200
>>>Jiri Pirko<jpirko@...hat.com>  wrote:
><snip>
>>>>+	rawp = skb->data;
>>>>+	if (*(unsigned short *) rawp == 0xFFFF)
>>>>+		/*
>>>>+		 * This is a magic hack to spot IPX packets. Older Novell
>>>>+		 * breaks the protocol design and runs IPX over 802.3 without
>>>>+		 * an 802.2 LLC layer. We look for FFFF which isn't a used
>>>>+		 * 802.2 SSAP/DSAP. This won't work for fault tolerant netware
>>>>+		 * but does for the rest.
>>>>+		 */
>>>>+		skb->protocol = htons(ETH_P_802_3);
>>>>+	else
>>>>+		/*
>>>>+		 * Real 802.2 LLC
>>>>+		 */
>>>>+		skb->protocol = htons(ETH_P_802_2);
>>>>+}
>>>
>>>What about doublely tagged packets?
>>
>>No problem. Once they are untagged and reinjected they are untagged
>>again and reinjected again:
>>
>>->  __netif_reveive_skb
>>vlan_untag
>>vlan_do_receive
>>->  __netif_receive_skb
>>vlan_untag
>>vlan_do_receive
>
>Hi Jiri,
>
>Instead of untagging and reinjecting, wouldn't it be possible to
>remove all 802.1Q headers in a loop and directly deliver the untagged
>skb? Are there any hw-accel implementations that remove several level
>of tagging?

Makes no sense to untag multiple tags in loop at once. For each tag you
need to call vlan_do_receive so the frame could be properly processed by
vlan code.

I'm not aware of a possibility of hwaccel to untag multiple tags at
once. Honestly I cannot imagine how that could be handled (maybe setting
array of vlan_tcis).

Jirka

>
>	Nicolas.
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