Subject: Re: [net-next rfc V3 8/9] macvtap: add TUNSETQUEUE ioctl

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 5 Jun 2013 13:59:28 +0300

On Wed, Jun 05, 2013 at 02:36:31PM +0800, Jason Wang wrote:
> This patch adds TUNSETQUEUE ioctl to let userspace can temporarily disable or
> enable a queue of macvtap. This is used to be compatible at API layer of tuntap
> to simplify the userspace to manage the queues. This is done through introducing
> a linked list to track all taps while using vlan->taps array to only track
> active taps.
> 
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>  drivers/net/macvtap.c      |  133 +++++++++++++++++++++++++++++++++++++++-----
>  include/linux/if_macvlan.h |    4 +
>  2 files changed, 122 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 14764cc..355e6ad 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -45,6 +45,8 @@ struct macvtap_queue {
>  	struct file *file;
>  	unsigned int flags;
>  	u16 queue_index;
> +	bool enabled;
> +	struct list_head next;
>  };
>  
>  static struct proto macvtap_proto = {
> @@ -85,14 +87,37 @@ static const struct proto_ops macvtap_socket_ops;
>   */
>  static DEFINE_SPINLOCK(macvtap_lock);
>  
> -static int macvtap_set_queue(struct net_device *dev, struct file *file,
> +static int macvtap_enable_queue(struct net_device *dev, struct file *file,
>  				struct macvtap_queue *q)
>  {
>  	struct macvlan_dev *vlan = netdev_priv(dev);
> +	int err = -EINVAL;
> +
> +	spin_lock(&macvtap_lock);
> +
> +	if (q->enabled)
> +		goto out;
> +
> +	err = 0;
> +	rcu_assign_pointer(vlan->taps[vlan->numvtaps], q);
> +	q->queue_index = vlan->numvtaps;
> +	q->enabled = true;
> +
> +	vlan->numvtaps++;
> +	vlan->numdisabled--;
> +out:
> +	spin_unlock(&macvtap_lock);
> +	return err;
> +}
> +
> +static int macvtap_set_queue(struct net_device *dev, struct file *file,
> +			     struct macvtap_queue *q)
> +{
> +	struct macvlan_dev *vlan = netdev_priv(dev);
>  	int err = -EBUSY;
>  
>  	spin_lock(&macvtap_lock);
> -	if (vlan->numvtaps == MAX_MACVTAP_QUEUES)
> +	if (vlan->numvtaps + vlan->numdisabled == MAX_MACVTAP_QUEUES)
>  		goto out;
>  
>  	err = 0;
> @@ -102,7 +127,9 @@ static int macvtap_set_queue(struct net_device *dev, struct file *file,
>  
>  	q->file = file;
>  	q->queue_index = vlan->numvtaps;
> +	q->enabled = true;
>  	file->private_data = q;
> +	list_add_tail(&q->next, &vlan->tap_link);
>  
>  	vlan->numvtaps++;
>  
> @@ -111,6 +138,38 @@ out:
>  	return err;
>  }
>  
> +static int macvtap_disable_queue(struct macvtap_queue *q)
> +{
> +	struct macvlan_dev *vlan;
> +	struct macvtap_queue *nq;
> +	int err = 0;
> +
> +	spin_lock(&macvtap_lock);
> +	vlan = rcu_dereference_protected(q->vlan,
> +					 lockdep_is_held(&macvtap_lock));
> +
> +	if (!q->enabled) {
> +		err = -EINVAL;
> +		goto out;
> +	}
> +
> +	if (vlan) {
> +		int index = q->queue_index;
> +		nq = rcu_dereference_protected(vlan->taps[vlan->numvtaps - 1],
> +					       lockdep_is_held(&macvtap_lock));
> +		nq->queue_index = index;
> +
> +		rcu_assign_pointer(vlan->taps[index], nq);
> +		RCU_INIT_POINTER(vlan->taps[vlan->numvtaps - 1], NULL);
> +		q->enabled = false;
> +
> +		vlan->numvtaps--;
> +		vlan->numdisabled++;
> +	}
> +out:
> +	spin_unlock(&macvtap_lock);
> +	return err;
> +}
>  /*
>   * The file owning the queue got closed, give up both
>   * the reference that the files holds as well as the
> @@ -128,18 +187,24 @@ static void macvtap_put_queue(struct macvtap_queue *q)
>  	vlan = rcu_dereference_protected(q->vlan,
>  					 lockdep_is_held(&macvtap_lock));
>  	if (vlan) {
> +		int numvtaps = vlan->numvtaps;
>  		int index = q->queue_index;
> -		BUG_ON(index >= vlan->numvtaps);
>  
> -		nq = rcu_dereference_protected(vlan->taps[vlan->numvtaps - 1],
> -					       lockdep_is_held(&macvtap_lock));
> -		rcu_assign_pointer(vlan->taps[index], nq);
> -		nq->queue_index = index;
> +		if (q->enabled) {
> +			BUG_ON(index >= vlan->numvtaps);
> +			nq = rcu_dereference_protected(vlan->taps[numvtaps - 1],
> +						lockdep_is_held(&macvtap_lock));
> +			rcu_assign_pointer(vlan->taps[index], nq);

Do we really need these tricks?
Can't we call macvtap_disable_queue and then only handle disable queues
here?

> +			nq->queue_index = index;
> +
> +			RCU_INIT_POINTER(vlan->taps[numvtaps - 1], NULL);
> +			vlan->numvtaps--;
> +		} else
> +			vlan->numdisabled--;
>  
> -		RCU_INIT_POINTER(vlan->taps[vlan->numvtaps - 1], NULL);
>  		RCU_INIT_POINTER(q->vlan, NULL);
>  		sock_put(&q->sk);
> -		--vlan->numvtaps;
> +		list_del_init(&q->next);
>  	}
>  
>  	spin_unlock(&macvtap_lock);
> @@ -160,6 +225,10 @@ static struct macvtap_queue *macvtap_get_queue(struct net_device *dev,
>  {
>  	struct macvlan_dev *vlan = netdev_priv(dev);
>  	struct macvtap_queue *tap = NULL;
> +	/* numvtaps here is just a hint, even if the number of active taps were
> +	 * reduced in the same sime,

typo

> since we are protected by rcu read lock,
> +	 * we're safe here.

I don't really understand what is this comment trying to say.
What is protected? What is safe? safe time as what?

> +	 */
>  	int numvtaps = ACCESS_ONCE(vlan->numvtaps);
>  	__u32 rxq;
>  
> @@ -196,20 +265,25 @@ out:
>  static void macvtap_del_queues(struct net_device *dev)
>  {
>  	struct macvlan_dev *vlan = netdev_priv(dev);
> -	struct macvtap_queue *q, *qlist[MAX_MACVTAP_QUEUES];
> +	struct macvtap_queue *q, *tmp, *qlist[MAX_MACVTAP_QUEUES];
>  	int i, j = 0;
>  
>  	spin_lock(&macvtap_lock);
> -	for (i = 0; i < vlan->numvtaps; i++) {
> -		q = rcu_dereference_protected(vlan->taps[i],
> -					      lockdep_is_held(&macvtap_lock));
> -		BUG_ON(q == NULL);
> +	list_for_each_entry_safe(q, tmp, &vlan->tap_link, next) {
> +		list_del_init(&q->next);
>  		qlist[j++] = q;
> -		RCU_INIT_POINTER(vlan->taps[i], NULL);
>  		RCU_INIT_POINTER(q->vlan, NULL);
> +		if (q->enabled)
> +			vlan->numvtaps--;
> +		else
> +			vlan->numdisabled--;
>  	}
> +	for (i = 0; i < vlan->numvtaps; i++)
> +		RCU_INIT_POINTER(vlan->taps[i], NULL);
> +	BUG_ON(vlan->numvtaps + vlan->numdisabled != 0);

Better two BUG_ON checks - they are both 0 right?
And no need for != 0.

>  	/* guarantee that any future macvtap_set_queue will fail */
>  	vlan->numvtaps = MAX_MACVTAP_QUEUES;
> +	vlan->numdisabled = 0;

What's this doing? We know it's 0 ...

>  	spin_unlock(&macvtap_lock);
>  
>  	synchronize_rcu();
> @@ -298,6 +372,9 @@ static int macvtap_newlink(struct net *src_net,
>  			   struct nlattr *tb[],
>  			   struct nlattr *data[])
>  {
> +	struct macvlan_dev *vlan = netdev_priv(dev);
> +	INIT_LIST_HEAD(&vlan->tap_link);
> +
>  	/* Don't put anything that may fail after macvlan_common_newlink
>  	 * because we can't undo what it does.
>  	 */
> @@ -926,6 +1003,27 @@ static int macvtap_set_iff(struct file *file, struct ifreq __user *ifr_u)
>  	return 0;
>  }
>  
> +static int macvtap_ioctl_set_queue(struct file *file, unsigned int flags)
> +{
> +	struct macvtap_queue *q = file->private_data;
> +	struct macvlan_dev *vlan;
> +	int ret = -EINVAL;
> +
> +	vlan = macvtap_get_vlan(q);
> +	if (!vlan)
> +		goto done;

Can be just return -EINVAL, and you won't need to initialize
above.

> +
> +	if (flags & IFF_ATTACH_QUEUE)
> +		ret = macvtap_enable_queue(vlan->dev, file, q);
> +	else if (flags & IFF_DETACH_QUEUE)
> +		ret = macvtap_disable_queue(q);
> +
> +	macvtap_put_vlan(vlan);
> +
> +done:
> +	return ret;
> +}
> +
>  /*
>   * provide compatibility with generic tun/tap interface
>   */
> @@ -958,6 +1056,11 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
>  		macvtap_put_vlan(vlan);
>  		return ret;
>  
> +	case TUNSETQUEUE:
> +		if (get_user(u, &ifr->ifr_flags))
> +			return -EFAULT;
> +		return macvtap_ioctl_set_queue(file, u);
> +
>  	case TUNGETFEATURES:
>  		if (put_user(IFF_TAP | IFF_NO_PI | IFF_VNET_HDR, up))
>  			return -EFAULT;
> diff --git a/include/linux/if_macvlan.h b/include/linux/if_macvlan.h
> index 62d8bda..87b9091 100644
> --- a/include/linux/if_macvlan.h
> +++ b/include/linux/if_macvlan.h
> @@ -69,8 +69,12 @@ struct macvlan_dev {
>  	u16			flags;
>  	int (*receive)(struct sk_buff *skb);
>  	int (*forward)(struct net_device *dev, struct sk_buff *skb);
> +	/* This array tracks active taps. */
>  	struct macvtap_queue	*taps[MAX_MACVTAP_QUEUES];
> +	/* This list tracks all taps (both enabled and disabled) */
> +	struct list_head	tap_link;

Bad name, e.g. queue_list would be better.

>  	int			numvtaps;
> +	int			numdisabled;

So numvtaps is number of entries in the taps array.
But to get items on list, you must add numdisabled and
numvtaps, that's confusing.
Instead of numdisabled, let's add a counter for
number of entries in the tap_link list.

How about numqueues?

>  	int			minor;
>  };
> -- 
> 1.7.1