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

From: Vlad Yasevich <[email-masked]>
Date: Wed, 19 Jun 2013 11:47:42 -0400

On 06/19/2013 11:16 AM, Michael S. Tsirkin wrote:
> 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);

OK

>
>> +}
>> +
>>   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".
>

Isn't a user space write to TUN exactly the same as
a user space write to macvtap?  It looks to me like the
are and so features for them would work the same way.

macvlan and macvtap would be different, but I think that's
to be expected.

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

By surprising do you mean that if user space writes
a TSO packet to a macvtap where TSO is disabled, the TSO
packet is still sent to the network?

>
>> +	}
>> +
>> +	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