netdev - Re: [PATCH v2] net: tso: add support for IPv6

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Date:	Mon, 26 Oct 2015 17:13:24 +0900
From:	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:	"Grumbach, Emmanuel" <emmanuel.grumbach@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"egrumbach@...il.com" <egrumbach@...il.com>
Subject: Re: [PATCH v2] net: tso: add support for IPv6

On 2015/10/26 16:47, Grumbach, Emmanuel wrote:
> On 10/26/2015 06:03 AM, Toshiaki Makita wrote:
>> On 2015/10/26 5:02, Emmanuel Grumbach wrote:
>>> Adding IPv6 for the TSO helper API is trivial:
>>> * Don't play with the id (which doesn't exist in IPv6)
>>> * Correctly update the payload_len (don't include the
>>>   length of the IP header itself)
>> ...
>>>  	memcpy(hdr, skb->data, hdr_len);
>>> -	iph = (struct iphdr *)(hdr + mac_hdr_len);
>>> -	iph->id = htons(tso->ip_id);
>>> -	iph->tot_len = htons(size + hdr_len - mac_hdr_len);
>>> +	if (skb->protocol == htons(ETH_P_IP)) {
>>
>> I guess this should be vlan_get_protocol(skb).
> 
> I truly don't know. I guess we could have VLANs, but I'd need to check
> how the packet would look like after it exits mac80211.

I don't know much about mac80211.

What I see is that mvneta has TSO in vlan_features and it uses
tso_build_hdr(). When vlan device is used, we cannot access network
protocol by skb->protocol without HW vlan acceleration.
So it looks like this change corrupts TSO functionality on mvneta.

> If we need that, I'll likely do this check once in tso_start() and add a
> variable to struct tso_t.

I'm not sure if an additional variable is needed.
At least, skb_network_offset()/ip_hdr() should correctly handle (skip)
vlan headers.

Toshiaki Makita

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