netdev - Re: [RFC v2 1/3] vsockmon: Add tap functions

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Message-ID: <20160630104912.GB31866@stefanha-x1.localdomain>
Date:	Thu, 30 Jun 2016 11:49:12 +0100
From:	Stefan Hajnoczi <stefanha@...hat.com>
To:	ggarcia@...a.uab.cat
Cc:	netdev@...r.kernel.org, jhansen@...are.com
Subject: Re: [RFC v2 1/3] vsockmon: Add tap functions

On Wed, Jun 22, 2016 at 06:11:00PM +0200, ggarcia@...a.uab.cat wrote:
> +int __vsock_remove_tap(struct vsock_tap *vt) {

This function should be static, it's not used outside this source file.

> +static int __vsock_deliver_tap_skb(struct sk_buff *skb,
> +				     struct net_device *dev)
> +{
> +	int ret = 0;
> +
> +	if (skb) {
> +		dev_hold(dev);

I don't understand the need for this dev_hold()/dev_put().  Can anyone
explain why it is necessary?

> +		/* Take skb ownership so it is not consumed in dev_queue_xmit.
> +		 * dev_queue_xmit will drop a reference so the reference count
> +		 * will reset.
> +		 */
> +		skb_get(skb);
> +		skb->dev = dev;
> +		ret = dev_queue_xmit(skb);
> +		if (unlikely(ret > 0))
> +			ret = net_xmit_errno(ret);
> +
> +		dev_put(dev);
> +	}
> +
> +	return ret;
> +}

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