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Date: Thu, 15 Aug 2013 14:59:01 -0400
From: Vlad Yasevich <vyasevic@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: netdev@...r.kernel.org
Subject: Re: [PATCH v3 2/2] macvtap: Allow tap features change when IFF_VNET_HDR
is disabled.
On 08/15/2013 02:48 PM, Michael S. Tsirkin wrote:
> On Thu, Aug 15, 2013 at 02:39:39PM -0400, Vlad Yasevich wrote:
>> On 08/15/2013 01:33 PM, Michael S. Tsirkin wrote:
>>> 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 <vyasevic@...hat.com>
>>>> ---
>>>> 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.
>>
>> Why?
>> The whole point it not to change features on SETIFF, so that
>> they are preserved for when the flags change again. It just that
>> flag values either allow whatever offload user specified (correctly
>> masked via netdev_update_features) or turn off all offloads at the tap.
>>
>> -vlad
>
> That's the point. As it is, if flag value changes, we don't call
> netdev_update_features so offloads aren't masked/unmasked.
>
> Example:
>
> 1. SETOFFLOADS to enable
> 2. VNET = 0
>
> offloads are still enabled
>
But unused since since VNET=0. I am trying to be careful not to
break things when ioctl calls get all inverted and reversed, but
may be I am trying too hard and we should just let things break.
I just feels kinds of silly since the app may now know all the
details, but the kernel does and can do the "right thing".
-vlad
>
>>>> /*
>>>> * 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
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