netdev - Re: [PATCH][v3] dev : fix mtu check when TSO is enabled

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Message-Id: <20110314.165929.232913682.davem@davemloft.net>
Date:	Mon, 14 Mar 2011 16:59:29 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	daniel.lezcano@...e.fr
Cc:	eric.dumazet@...il.com, kaber@...sh.net, nightnord@...il.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH][v3] dev : fix mtu check when TSO is enabled

From: Daniel Lezcano <daniel.lezcano@...e.fr>
Date: Mon, 14 Mar 2011 21:39:50 +0100

> +	len = dev->mtu + dev->hard_header_len + VLAN_HLEN;
> +	if (skb->len < len)
> +		return true;

This is not a correct translation of the original test:

> -		     (skb->len > (dev->mtu + dev->hard_header_len + VLAN_HLEN)))) {

You need to use "<=" in your version, which currently rejects all
full sized frames. :-)

> +
> +	/* if TSO is enabled, we don't care about the length as the packet
> +	 * could be forwarded without being segmented before
> +	 */
> +	if (skb->dev && skb->dev->features & NETIF_F_TSO)
> +		return true;

I am trying to understand why you aren't simply checking also if this
is a segmented frame?  Perhaps skb_is_gso() && device has NETIF_F_TSO
set?

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