Subject: Re: [PATCH net-next 1/2] macvtap: Let TUNSETOFFLOAD actually controll offload features.

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 19 Jun 2013 18:16:34 +0300

On Wed, Jun 19, 2013 at 10:47:51AM -0400, Vlad Yasevich wrote:
> When the user issues TUNSETOFFLOAD ioctl, macvtap does not do
> anything other then to verify arguments.  This patch adds
> functionality to allow users to actually control offload features.
> NETIF_F_GSO and NETIF_F_GRO are always on, but the rest of the
> features can be controlled.
> 
> Signed-off-by: Vlad Yasevich <[email-masked]>
> ---
>  drivers/net/macvlan.c      |  9 +++++++++
>  drivers/net/macvtap.c      | 41 ++++++++++++++++++++++++++++++++++++++++-
>  include/linux/if_macvlan.h |  1 +
>  3 files changed, 50 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
> index edfddc5..fa47415 100644
> --- a/drivers/net/macvlan.c
> +++ b/drivers/net/macvlan.c
> @@ -638,6 +638,14 @@ static int macvlan_ethtool_get_settings(struct net_device *dev,
>  	return __ethtool_get_settings(vlan->lowerdev, cmd);
>  }
>  
> +static netdev_features_t macvlan_fix_features(struct net_device *dev,
> +					      netdev_features_t features)
> +{
> +	struct macvlan_dev *vlan = netdev_priv(dev);
> +
> +	return (features & vlan->set_features) | (features & ~MACVLAN_FEATURES);

A bit clearer as

> +	return features & (vlan->set_features | ~MACVLAN_FEATURES);

> +}
> +
>  static const struct ethtool_ops macvlan_ethtool_ops = {
>  	.get_link		= ethtool_op_get_link,
>  	.get_settings		= macvlan_ethtool_get_settings,
> @@ -651,6 +659,7 @@ static const struct net_device_ops macvlan_netdev_ops = {
>  	.ndo_stop		= macvlan_stop,
>  	.ndo_start_xmit		= macvlan_start_xmit,
>  	.ndo_change_mtu		= macvlan_change_mtu,
> +	.ndo_fix_features	= macvlan_fix_features,
>  	.ndo_change_rx_flags	= macvlan_change_rx_flags,
>  	.ndo_set_mac_address	= macvlan_set_mac_address,
>  	.ndo_set_rx_mode	= macvlan_set_mac_lists,
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 5a76f20..09f0b1f 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -976,6 +976,45 @@ static int macvtap_ioctl_set_queue(struct file *file, unsigned int flags)
>  	return ret;
>  }
>  
> +static int set_offload(struct macvtap_queue *q, unsigned long arg)
> +{
> +	struct macvlan_dev *vlan;
> +	netdev_features_t features = NETIF_F_GSO|NETIF_F_GRO;
> +	int err = 0;
> +
> +	if (arg & TUN_F_CSUM) {
> +		features = NETIF_F_HW_CSUM;
> +
> +		if (arg & (TUN_F_TSO4 | TUN_F_TSO6)) {
> +			if (arg & TUN_F_TSO_ECN)
> +				features |= NETIF_F_TSO_ECN;
> +			if (arg & TUN_F_TSO4)
> +				features |= NETIF_F_TSO;
> +			if (arg & TUN_F_TSO6)
> +				features |= NETIF_F_TSO6;
> +		}
> +
> +		if (arg & TUN_F_UFO)
> +			features |= NETIF_F_UFO;

Hmm this looks strange. The meaning of offloads
with tun is exactly the reverse from vlan/macvtap.

For example, assume that you disable TSO.
For tun this means: "don't send TSO packets to userspace".
What this patch makes it mean for macvtap is
"don't send TSO packets from userspace on the network".

So, userspace using this ioctl
to control tun would get a surprising result.

> +	}
> +
> +	rtnl_lock();
> +	rcu_read_lock_bh();
> +	vlan = rcu_dereference_bh(q->vlan);
> +	if (!vlan) {
> +		err = -ENOLINK;
> +		goto unlock;
> +	}
> +
> +	vlan->set_features = features;
> +	netdev_update_features(vlan->dev);
> +
> +unlock:
> +	rcu_read_unlock_bh();
> +	rtnl_unlock();
> +	return err;
> +}
> +
>  /*
>   * provide compatibility with generic tun/tap interface
>   */
> @@ -1062,7 +1101,7 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
>  			 got enabled for forwarded frames */
>  		if (!(q->flags & IFF_VNET_HDR))
>  			return  -EINVAL;
> -		return 0;
> +		return set_offload(q, arg);
>  
>  	default:
>  		return -EINVAL;
> diff --git a/include/linux/if_macvlan.h b/include/linux/if_macvlan.h
> index f49a9f6..e446e82 100644
> --- a/include/linux/if_macvlan.h
> +++ b/include/linux/if_macvlan.h
> @@ -65,6 +65,7 @@ struct macvlan_dev {
>  
>  	DECLARE_BITMAP(mc_filter, MACVLAN_MC_FILTER_SZ);
>  
> +	netdev_features_t	set_features;
>  	enum macvlan_mode	mode;
>  	u16			flags;
>  	int (*receive)(struct sk_buff *skb);
> -- 
> 1.8.1.4