netdev - Re: [PATCH 1/2] net: Disable LRO on devices that are forwarding

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Message-ID: <20080620111139.GB29360@solarflare.com>
Date:	Fri, 20 Jun 2008 12:11:41 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, linux-net-drivers@...arflare.com,
	Kieran Mansley <kmansley@...arflare.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: [PATCH 1/2] net: Disable LRO on devices that are forwarding

Ben Hutchings wrote:
[...]
> diff --git a/net/core/dev.c b/net/core/dev.c
> index a495f71..f6944ec 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
[...]
> @@ -1123,6 +1124,29 @@ int dev_close(struct net_device *dev)
>  }
>  
>  
> +/**
> + *	dev_disable_lro - disable Large Receive Offload on a device
> + *	@dev: device
> + *
> + *	Disable Large Receive Offload (LRO) on a net device.  Must be
> + *	called under RTNL.  This is needed if received packets may be
> + *	forwarded to another interface.
> + */
> +void dev_disable_lro(struct net_device *dev)
> +{
> +	if (dev->ethtool_ops && dev->ethtool_ops->get_flags &&
> +	    dev->ethtool_ops->set_flags) {
> +		u32 flags = dev->ethtool_ops->get_flags(dev);
> +		if (flags & ETH_FLAG_LRO) {
> +			flags &= ~ETH_FLAG_LRO;
> +			dev->ethtool_ops->set_flags(dev, flags);
> +		}
> +	}
> +	WARN_ON(dev->features & NETIF_F_LRO);
> +}
> +EXPORT_SYMBOL(dev_disable_lro);
[...]

Of course, this doesn't work where the device that's about to start
forwarding is a VLAN device, bonding device or other device depending on
the physical device which is doing LRO.

It might be worth separating out the offload control ops from ethtool ops
since they could usefully be applied to other device types... particularly
here.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
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