netdev - Re: [v4 Patch 1/2] s2io: add dynamic LRO disable support

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Message-Id: <1277207080.2091.2.camel@achroite.uk.solarflarecom.com>
Date:	Tue, 22 Jun 2010 12:44:40 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Amerigo Wang <amwang@...hat.com>
Cc:	netdev@...r.kernel.org, nhorman@...hat.com, sgruszka@...hat.com,
	herbert.xu@...hat.com, Ramkrishna.Vepa@...r.com,
	davem@...emloft.net
Subject: Re: [v4 Patch 1/2] s2io: add dynamic LRO disable support

On Tue, 2010-06-22 at 04:50 -0400, Amerigo Wang wrote:
> This patch adds dynamic LRO diable support for s2io net driver.
> 
> (I don't have s2io card, so only did compiling test. Anyone who wants
> to test this is more than welcome.)
> 
> This is based on Neil's initial work, and heavily modified
> based on Ramkrishna's suggestions.
[...]
> +static int s2io_ethtool_set_flags(struct net_device *dev, u32 data)
> +{
> +	struct s2io_nic *sp = netdev_priv(dev);
> +	int rc = 0;
> +	int changed = 0;
> +
> +	if (data & ~ETH_FLAG_LRO)
> +		return -EOPNOTSUPP;
> +
> +	if (data & ETH_FLAG_LRO) {
> +		if (lro_enable) {
> +			if (!(dev->features & NETIF_F_LRO)) {
> +				dev->features |= NETIF_F_LRO;
> +				changed = 1;
> +			}
> +		} else
> +			rc = -EOPNOTSUPP;

Should lro_enable=0 really prevent enabling it later?  This seems
unusual.

> +	} else if (dev->features & NETIF_F_LRO) {
> +		dev->features &= ~NETIF_F_LRO;
> +		changed = 1;
> +	}
> +
> +	if (changed && netif_running(dev)) {
> +		s2io_stop_all_tx_queue(sp);
> +		s2io_card_down(sp);
> +		sp->lro = dev->features & NETIF_F_LRO;
[...]

This means s2io_nic::lro and ring_info::lro can have the value
NETIF_F_LRO, where previously they would only have the value 0 or 1.  I
don't know whether this could be a problem, but the safe thing to do is
to coerce the value by writing !!(dev->features & NETIF_F_LRO).

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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