netdev - Re: NETIF_F_TSO vs NETIF_F_TSO{6,

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Message-ID: <20110405180337.GA16977@rere.qmqm.pl>
Date:	Tue, 5 Apr 2011 20:03:37 +0200
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: NETIF_F_TSO vs NETIF_F_TSO{6,_ECN}

On Tue, Apr 05, 2011 at 04:50:02PM +0100, Ben Hutchings wrote:
> According to the commit that introduced NETIF_F_TSO6
> (f83ef8c0b58dac17211a4c0b6df0e2b1bd6637b1):
>     
>         This patch will introduce a new flag NETIF_F_TSO6 which will be used
>         to check whether device supports TSO over IPv6. If device support TSO
>         over IPv6 then we don't clear of NETIF_F_TSO and which will make the
>         TCP layer to create TSO packets. Any device supporting TSO over IPv6
>         will set NETIF_F_TSO6 flag in "dev->features" along with NETIF_F_TSO.
>     
>         In case when user disables TSO using ethtool, NETIF_F_TSO will get
>         cleared from "dev->features". So even if we have NETIF_F_TSO6 we don't
>         get TSO packets created by TCP layer.
> 
> So I think we need to either:
> 1. Disallow toggling NETIF_F_TSO6 (following the previous rule)
> 2. Disable NETIF_F_TSO6 when NETIF_F_TSO is disabled
> 
> The same presumably applies to NETIF_F_TSO_ECN.

There seems to be no such dependency in the networking code. I.e. TSO6
should just work with TSO4 disabled.

Best Regards,
Michał Mirosław
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