Subject: Re: [PATCH net-next] tun: return NET_XMIT_DROP for dropped packets

From: Amos Kong <[email-masked]>
Date: Wed, 19 Nov 2014 00:53:59 +0800

On Tue, Nov 18, 2014 at 01:20:41PM +0800, Jason Wang wrote:
> After commit 5d097109257c03a71845729f8db6b5770c4bbedc
> ("tun: only queue packets on device"), NETDEV_TX_OK was returned for
> dropped packets. This will confuse pktgen since dropped packets were
> counted as sent ones.
> 
> Fixing this by returning NET_XMIT_DROP to let pktgen count it as error
> packet.
> 
> Cc: Michael S. Tsirkin <[email-masked]>
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>  drivers/net/tun.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index e3fa65a..ac53a73 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -819,7 +819,7 @@ drop:
>  	skb_tx_error(skb);
>  	kfree_skb(skb);
>  	rcu_read_unlock();
> -	return NETDEV_TX_OK;
> +	return NET_XMIT_DROP;

Quoted from linux/drivers/firewire/net.c:

  /*
   * FIXME: According to a patch from 2003-02-26, "returning non-zero
   * causes serious problems" here, allegedly.  Before that patch,
   * -ERRNO was returned which is not appropriate under Linux 2.6.
   * Perhaps more needs to be done?  Stop the queue in serious
   * conditions and restart it elsewhere?
   */

I saw many drivers return NETDEV_TX_OK in xmit for drop packets, eg: virtio_net.c

>  }
>  
>  static void tun_net_mclist(struct net_device *dev)
> -- 
> 1.9.1

-- 
			Amos.