Subject: Re: [PATCH v3 2/2] macvtap: Allow tap features change when IFF_VNET_HDR is disabled.

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 15 Aug 2013 20:33:47 +0300

On Thu, Aug 15, 2013 at 01:02:53PM -0400, Vlad Yasevich wrote:
> When the user turns off IFF_VNET_HDR flag, attempts to change
> offload features via TUNSETOFFLOAD do not work.  This could cause
> GSO packets to be delivered to the user when the user is
> not prepared to handle them.
> 
> To solve, allow processing of TUNSETOFFLOAD when IFF_VNET_HDR is
> disabled.  Also, take the setting of IFF_VNET_HDR into consideration
> when determining the feature set to apply to incommig traffic.
> If IFF_VNET_HDR is set, we use user-specfied feature set.  if the
> IFF_VNET_HDR is clear, we mask off all tun-specific offload features,
> since user can not be notified of the possbile offloads.
> 
> Signed-off-by: Vlad Yasevich <[email-masked]>
> ---
>  drivers/net/macvtap.c | 30 ++++++++++++++++++++++++------
>  1 file changed, 24 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 8121358..df45a59 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -269,6 +269,28 @@ static void macvtap_del_queues(struct net_device *dev)
>  		sock_put(&qlist[j]->sk);
>  }
>  
> +/* Determine features to be applied to the packet as it

/*
 * Please use comments
 * like this
 */

> + * gets sent to the tap.  The features depend on the offloads
> + * set by user and by whether or not IFF_VNET_HDR is enabled.
> + */
> +static netdev_features_t macvtap_skb_features(struct sk_buff *skb,
> +					      struct macvtap_queue *q)
> +{
> +	struct macvlan_dev *vlan = netdev_priv(skb->dev);
> +	netdev_features_t features = netif_skb_features(skb);
> +
> +	/* If VNET_HDR is enabled, user can receive offload info so
> +	 * use user-specified tap_features.
> +	 * Otherwise, mask off all tap offload features.
> +	 */
> +	if (q->flags & IFF_VNET_HDR)
> +		features &= vlan->tap_features;
> +	else
> +		features &= ~TUN_OFFLOADS;
> +
> +	return features;
> +}
> +

Okay, but this means we need to do netdev_update_features
on SETIFF since it changes q->flags.

>  /*
>   * Forward happens for data that gets sent from one macvlan
>   * endpoint to another one in bridge mode. We just take
> @@ -276,9 +298,9 @@ static void macvtap_del_queues(struct net_device *dev)
>   */
>  static int macvtap_forward(struct net_device *dev, struct sk_buff *skb)
>  {
> -	struct macvlan_dev *vlan = netdev_priv(dev);
>  	struct macvtap_queue *q = macvtap_get_queue(dev, skb);
>  	netdev_features_t features;
> +
>  	if (!q)
>  		goto drop;
>  
> @@ -289,7 +311,7 @@ static int macvtap_forward(struct net_device *dev, struct sk_buff *skb)
>  	/* Apply the forward feature mask so that we perform segmentation
>  	 * according to users wishes.
>  	 */
> -	features = netif_skb_features(skb) & vlan->tap_features;
> +	features = macvtap_skb_features(skb, q);
>  	if (netif_needs_gso(skb, features)) {
>  		struct sk_buff *segs = __skb_gso_segment(skb, features, false);
>  
> @@ -1161,10 +1183,6 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
>  			    TUN_F_TSO_ECN | TUN_F_UFO))
>  			return -EINVAL;
>  
> -		/* TODO: only accept frames with the features that
> -			 got enabled for forwarded frames */
> -		if (!(q->flags & IFF_VNET_HDR))
> -			return  -EINVAL;
>  		rtnl_lock();
>  		ret = set_offload(q, arg);
>  		rtnl_unlock();
> -- 
> 1.8.1.4