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Message-ID: <20130523115206.GD17993@redhat.com>
Date: Thu, 23 May 2013 14:52:06 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [net-next RFC 7/8] macvtap: add TUNSETQUEUE ioctl
On Thu, May 23, 2013 at 11:12:32AM +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 by just introduce a pointer detached which was set when the queue
> were detached. Only the queue with NULL set to this pointer can be used to
> forward packets.
>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
Isn't this a bit too tricky?
Why keep disabled queues on the array at all?
Let's add a linked list of all queues for accounting.
Use array for enabled queues only, for data path.
> ---
> drivers/net/macvtap.c | 147 +++++++++++++++++++++++++++++++++++--------
> include/linux/if_macvlan.h | 7 ++
> 2 files changed, 126 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index e3f9344..06b10a5 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -85,67 +85,131 @@ static const struct proto_ops macvtap_socket_ops;
> */
> static DEFINE_SPINLOCK(macvtap_lock);
>
> +static void macvtap_swap_slot(struct macvlan_dev *vlan, int a, int b)
> +{
> + struct macvtap_queue *q1, *q2;
> +
> + if (a == b)
> + return;
> +
> + q1 = rcu_dereference_protected(vlan->taps[a],
> + lockdep_is_held(&macvtap_lock));
> + q2 = rcu_dereference_protected(vlan->taps[b],
> + lockdep_is_held(&macvtap_lock));
> +
> + BUG_ON(q1 == NULL || q2 == NULL);
> +
> + rcu_assign_pointer(vlan->taps[a], vlan->taps[b]);
> + rcu_assign_pointer(vlan->taps[b], q1);
> +
> + q1->queue_index = b;
> + q2->queue_index = a;
> +}
> +
> static int macvtap_set_queue(struct net_device *dev, struct file *file,
> - struct macvtap_queue *q)
> + struct macvtap_queue *q, bool enable)
> {
> struct macvlan_dev *vlan = netdev_priv(dev);
> int err = -EBUSY;
> + int total;
>
> spin_lock(&macvtap_lock);
> - if (vlan->numvtaps == MAX_MACVTAP_QUEUES)
> +
> + total = vlan->numvtaps + vlan->numdisabled;
> + if (!enable && total == MAX_MACVTAP_QUEUES)
> + goto out;
> +
> + err = -EINVAL;
> + if (enable && q->queue_index < vlan->numvtaps)
> goto out;
>
> err = 0;
> - rcu_assign_pointer(q->vlan, vlan);
> - rcu_assign_pointer(vlan->taps[vlan->numvtaps], q);
> - sock_hold(&q->sk);
>
> - q->file = file;
> - q->queue_index = vlan->numvtaps;
> - file->private_data = q;
> + if (enable) {
> + BUG_ON(q->queue_index >= total);
> + macvtap_swap_slot(vlan, q->queue_index, vlan->numvtaps);
> + --vlan->numdisabled;
> + } else {
> + rcu_assign_pointer(q->vlan, vlan);
> + rcu_assign_pointer(vlan->taps[total], q);
> + sock_hold(&q->sk);
> +
> + q->file = file;
> + q->queue_index = total;
> + file->private_data = q;
> + if (vlan->numdisabled)
> + macvtap_swap_slot(vlan, vlan->numvtaps, total);
> +
> + /* Make sure the pointers were seen before numvtaps. */
> + smp_wmb();
> + }
>
> vlan->numvtaps++;
> -
> 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
> - * one from the macvlan_dev if that still exists.
> + * The file owning the queue got closed or disabled.
> + *
> + * If closed give up both the reference that the files holds as well as the
> + * one from the macvlan_dev if that still exists. If disabled, reshuffle the
> + * array of taps.
> *
> * Using the spinlock makes sure that we don't get
> * to the queue again after destroying it.
> */
> -static void macvtap_put_queue(struct macvtap_queue *q)
> +static int macvtap_put_queue(struct macvtap_queue *q, bool clean)
s/clean/release/
and add a comment explaining what it is.
> {
> - struct macvtap_queue *nq;
> struct macvlan_dev *vlan;
> + int err = -EINVAL;
>
> spin_lock(&macvtap_lock);
> vlan = rcu_dereference_protected(q->vlan,
> lockdep_is_held(&macvtap_lock));
> +
> if (vlan) {
> + int total = vlan->numvtaps + vlan->numdisabled;
> int index = q->queue_index;
> - BUG_ON(index >= vlan->numvtaps);
> + bool disabled = q->queue_index >= vlan->numvtaps;
>
> - rcu_assign_pointer(vlan->taps[index],
> - vlan->taps[vlan->numvtaps - 1]);
> - RCU_INIT_POINTER(q->vlan, NULL);
> - nq = rcu_dereference_protected(vlan->taps[index],
> - lockdep_is_held(&macvtap_lock));
> - nq->queue_index = index;
> + if (!clean) {
> + BUG_ON(q->queue_index >= total);
> + if (q->queue_index >= vlan->numvtaps)
> + goto out;
> + }
>
> - sock_put(&q->sk);
> - --vlan->numvtaps;
> - }
> + err = 0;
> + macvtap_swap_slot(vlan, index, total - 1);
> + if (!disabled && vlan->numdisabled)
What's the logic here?
> + macvtap_swap_slot(vlan, index, vlan->numvtaps - 1);
So these swaps do a lot of RCU assign, presumably we need
synchronize_rcu as well?
> +
> + if (clean) {
> + RCU_INIT_POINTER(vlan->taps[total - 1], NULL);
> + RCU_INIT_POINTER(q->vlan, NULL);
> + sock_put(&q->sk);
> + if (disabled)
> + --vlan->numdisabled;
> + else
> + --vlan->numvtaps;
> + } else {
> + --vlan->numvtaps;
> + ++vlan->numdisabled;
> + }
> +
> + } else if (clean)
> + err = 0;
>
> +out:
> spin_unlock(&macvtap_lock);
>
> synchronize_rcu();
> - sock_put(&q->sk);
> +
> + if (clean)
> + sock_put(&q->sk);
> +
> + return err;
> }
>
> /*
> @@ -201,7 +265,7 @@ static void macvtap_del_queues(struct net_device *dev)
>
> /* macvtap_put_queue can free some slots, so go through all slots */
> spin_lock(&macvtap_lock);
> - for (i = 0; i < vlan->numvtaps; i++) {
> + for (i = 0; i < vlan->numvtaps + vlan->numdisabled; i++) {
> q = rcu_dereference_protected(vlan->taps[i],
> lockdep_is_held(&macvtap_lock));
> BUG_ON(q == NULL);
> @@ -211,6 +275,7 @@ static void macvtap_del_queues(struct net_device *dev)
> }
> /* guarantee that any future macvtap_set_queue will fail */
> vlan->numvtaps = MAX_MACVTAP_QUEUES;
> + vlan->numdisabled = 0;
> spin_unlock(&macvtap_lock);
>
> synchronize_rcu();
> @@ -384,7 +449,7 @@ static int macvtap_open(struct inode *inode, struct file *file)
> if ((dev->features & NETIF_F_HIGHDMA) && (dev->features & NETIF_F_SG))
> sock_set_flag(&q->sk, SOCK_ZEROCOPY);
>
> - err = macvtap_set_queue(dev, file, q);
> + err = macvtap_set_queue(dev, file, q, false);
> if (err)
> sock_put(&q->sk);
>
> @@ -398,7 +463,7 @@ out:
> static int macvtap_release(struct inode *inode, struct file *file)
> {
> struct macvtap_queue *q = file->private_data;
> - macvtap_put_queue(q);
> + macvtap_put_queue(q, true);
> return 0;
> }
>
> @@ -922,6 +987,27 @@ 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;
> +
> + if (flags & IFF_ATTACH_QUEUE)
> + ret = macvtap_set_queue(vlan->dev, file, q, true);
> + else if (flags & IFF_DETACH_QUEUE)
> + ret = macvtap_put_queue(q, false);
> +
> + macvtap_put_vlan(vlan);
> +
> +done:
> + return ret;
> +}
> +
> /*
> * provide compatibility with generic tun/tap interface
> */
> @@ -954,6 +1040,11 @@ 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 32e943a..f134afb 100644
> --- a/include/linux/if_macvlan.h
> +++ b/include/linux/if_macvlan.h
> @@ -69,8 +69,15 @@ struct macvlan_dev {
> u16 flags;
> int (*receive)(struct sk_buff *skb);
> int (*forward)(struct net_device *dev, struct sk_buff *skb);
> + /* This array tracks all taps (include disabled ones) and will be
> + * reshuffled to keep the following order:
> + * [0, numvtaps) : enabled taps,
> + * [numvtaps, numvtaps + numdisabled) : disabled taps,
> + * [numvtaps + numdisabled, MAX_MACVTAP_QUEUES) : unused slots
> + */
> struct macvtap_queue *taps[MAX_MACVTAP_QUEUES];
> int numvtaps;
> + int numdisabled;
> int minor;
> };
>
> --
> 1.7.1
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