linux-kernel - Re: [net-next rfc V3 7/9] macvtap: allow TUNSETIFF to create multiqueue device

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Date:	Wed, 5 Jun 2013 13:43:06 +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, sergei.shtylyov@...entembedded.com
Subject: Re: [net-next rfc V3 7/9] macvtap: allow TUNSETIFF to create
 multiqueue device

On Wed, Jun 05, 2013 at 02:36:30PM +0800, Jason Wang wrote:
> Though the queue were in fact created by open(), we still need to add this check
> to be compatible with tuntap which can let mgmt software use a single API to
> manage queues. This patch only validates the device name and moves the TUNSETIFF
> to a helper.
> 
> Signed-off-by: Jason Wang <jasowang@...hat.com>

The patch is OK, the description is confusing.
What you mean is simply:

	Allow IFF_MULTI_QUEUE in TUNSETIFF for macvtap, to match
	tun behaviour.

And if you put it like this, I would say make this
the last patch in the series, so userspace
can use IFF_MULTI_QUEUE to detect new versus old
behaviour.

> ---
>  drivers/net/macvtap.c |   51 ++++++++++++++++++++++++++++++++++++++----------
>  1 files changed, 40 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 5ccba99..14764cc 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -869,6 +869,7 @@ out:
>  	return ret;
>  }
>  
> +
>  static struct macvlan_dev *macvtap_get_vlan(struct macvtap_queue *q)
>  {
>  	struct macvlan_dev *vlan;

Please don't.

> @@ -887,6 +888,44 @@ static void macvtap_put_vlan(struct macvlan_dev *vlan)
>  	dev_put(vlan->dev);
>  }
>  
> +static int macvtap_set_iff(struct file *file, struct ifreq __user *ifr_u)
> +{
> +	struct macvtap_queue *q = file->private_data;
> +	struct net *net = current->nsproxy->net_ns;
> +	struct inode *inode = file_inode(file);
> +	struct net_device *dev, *dev2;
> +	struct ifreq ifr;
> +
> +	if (copy_from_user(&ifr, ifr_u, sizeof(struct ifreq)))
> +		return -EFAULT;
> +
> +	/* To keep the same behavior of tuntap, validate ifr_name */

So I'm not sure - why is it important to validate ifr_name here?
We ignore the name for all other flags - why is IFF_MULTI_QUEUE
special?

> +	if (ifr.ifr_flags & IFF_MULTI_QUEUE) {
> +		dev = __dev_get_by_name(net, ifr.ifr_name);
> +		if (!dev)
> +			return -EINVAL;
> +
> +		dev2 = dev_get_by_macvtap_minor(iminor(inode));
> +		if (!dev2)
> +			return -EINVAL;
> +
> +		if (dev != dev2) {
> +			dev_put(dev2);
> +			return -EINVAL;
> +		}
> +
> +		dev_put(dev2);
> +	}
> +
> +	if ((ifr.ifr_flags & ~(IFF_VNET_HDR | IFF_MULTI_QUEUE)) !=
> +	    (IFF_NO_PI | IFF_TAP))
> +		return -EINVAL;
> +	else
> +		q->flags = ifr.ifr_flags;
> +
> +	return 0;
> +}
> +
>  /*
>   * provide compatibility with generic tun/tap interface
>   */
> @@ -905,17 +944,7 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
>  
>  	switch (cmd) {
>  	case TUNSETIFF:
> -		/* ignore the name, just look at flags */

This is actually a useful comment that you've removed.

> -		if (get_user(u, &ifr->ifr_flags))
> -			return -EFAULT;
> -
> -		ret = 0;
> -		if ((u & ~IFF_VNET_HDR) != (IFF_NO_PI | IFF_TAP))
> -			ret = -EINVAL;
> -		else
> -			q->flags = u;
> -
> -		return ret;
> +		return macvtap_set_iff(file, ifr);
>  
>  	case TUNGETIFF:
>  		vlan = macvtap_get_vlan(q);
> -- 
> 1.7.1
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