Subject: Re: [PATCH net-next v3 2/4] netdevsim: forward skbs from one connected port to another

From: Jiri Pirko <[email-masked]>
Date: Fri, 15 Dec 2023 11:45:33 +0100

Thu, Dec 14, 2023 at 10:24:41PM CET, [email-masked] wrote:
>Forward skbs sent from one netdevsim port to its connected netdevsim
>port using dev_forward_skb, in a spirit similar to veth.

Perhaps better to write "dev_forward_skb()" to make obvious you talk
about function.

>
>Signed-off-by: David Wei <[email-masked]>
>---
> drivers/net/netdevsim/netdev.c | 23 ++++++++++++++++++-----
> 1 file changed, 18 insertions(+), 5 deletions(-)
>
>diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
>index e290c54b0e70..c5f53b1dbdcc 100644
>--- a/drivers/net/netdevsim/netdev.c
>+++ b/drivers/net/netdevsim/netdev.c
>@@ -29,19 +29,33 @@
> static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)
> {
> 	struct netdevsim *ns = netdev_priv(dev);
>+	struct netdevsim *peer_ns;
>+	int ret = NETDEV_TX_OK;
> 
>+	rcu_read_lock();

Why do you need to be in rcu read locked section here?

> 	if (!nsim_ipsec_tx(ns, skb))
>-		goto out;
>+		goto err;

Not sure why you need to rename the label. Why "out" is not okay?

> 
> 	u64_stats_update_begin(&ns->syncp);
> 	ns->tx_packets++;
> 	ns->tx_bytes += skb->len;
> 	u64_stats_update_end(&ns->syncp);
> 
>-out:
>-	dev_kfree_skb(skb);
>+	peer_ns = rcu_dereference(ns->peer);
>+	if (!peer_ns)
>+		goto err;

This is definitelly not an error path, "err" label name is misleading.

>+
>+	skb_tx_timestamp(skb);
>+	if (unlikely(dev_forward_skb(peer_ns->netdev, skb) == NET_RX_DROP))
>+		ret = NET_XMIT_DROP;

Hmm, can't you track dropped packets in ns->tx_dropped and expose in
nsim_get_stats64() ?

> 
>-	return NETDEV_TX_OK;
>+	rcu_read_unlock();
>+	return ret;
>+
>+err:
>+	rcu_read_unlock();
>+	dev_kfree_skb(skb);
>+	return ret;
> }
> 
> static void nsim_set_rx_mode(struct net_device *dev)
>@@ -302,7 +316,6 @@ static void nsim_setup(struct net_device *dev)
> 	eth_hw_addr_random(dev);
> 
> 	dev->tx_queue_len = 0;
>-	dev->flags |= IFF_NOARP;
> 	dev->flags &= ~IFF_MULTICAST;
> 	dev->priv_flags |= IFF_LIVE_ADDR_CHANGE |
> 			   IFF_NO_QUEUE;
>-- 
>2.39.3
>