Commit 9eb95228 authored by David Wei's avatar David Wei Committed by David S. Miller
Browse files

netdevsim: forward skbs from one connected port to another 



Forward skbs sent from one netdevsim port to its connected netdevsim
port using dev_forward_skb, in a spirit similar to veth.

Add a tx_dropped variable to struct netdevsim, tracking the number of
skbs that could not be forwarded using dev_forward_skb().

The xmit() function accessing the peer ptr is protected by an RCU read
critical section. The rcu_read_lock() is functionally redundant as since
v5.0 all softirqs are implicitly RCU read critical sections; but it is
useful for human readers.

If another CPU is concurrently in nsim_destroy(), then it will first set
the peer ptr to NULL. This does not affect any existing readers that
dereferenced a non-NULL peer. Then, in unregister_netdevice(), there is
a synchronize_rcu() before the netdev is actually unregistered and
freed. This ensures that any readers i.e. xmit() that got a non-NULL
peer will complete before the netdev is freed.

Any readers after the RCU_INIT_POINTER() but before synchronize_rcu()
will dereference NULL, making it safe.

The codepath to nsim_destroy() and nsim_create() takes both the newly
added nsim_dev_list_lock and rtnl_lock. This makes it safe with
concurrent calls to linking two netdevsims together.

Signed-off-by: default avatarDavid Wei <dw@davidwei.uk>
Reviewed-by: default avatarMaciek Machnikowski <maciek@machnikowski.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f532957d

drivers/net/netdevsim/netdev.c

+22 −5
Original line number Diff line number Diff line
@@ -29,18 +29,35 @@ 
static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)

{

	struct netdevsim *ns = netdev_priv(dev);

	unsigned int len = skb->len;

	struct netdevsim *peer_ns;



	rcu_read_lock();

	if (!nsim_ipsec_tx(ns, skb))

		goto out;

		goto out_drop_free;



	peer_ns = rcu_dereference(ns->peer);

	if (!peer_ns)

		goto out_drop_free;



	skb_tx_timestamp(skb);

	if (unlikely(dev_forward_skb(peer_ns->netdev, skb) == NET_RX_DROP))

		goto out_drop_cnt;



	rcu_read_unlock();

	u64_stats_update_begin(&ns->syncp);

	ns->tx_packets++;

	ns->tx_bytes += skb->len;

	ns->tx_bytes += len;

	u64_stats_update_end(&ns->syncp);

	return NETDEV_TX_OK;



out:

out_drop_free:

	dev_kfree_skb(skb);



out_drop_cnt:

	rcu_read_unlock();

	u64_stats_update_begin(&ns->syncp);

	ns->tx_dropped++;

	u64_stats_update_end(&ns->syncp);

	return NETDEV_TX_OK;

}
@@ -70,6 +87,7 @@ nsim_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats) 
		start = u64_stats_fetch_begin(&ns->syncp);

		stats->tx_bytes = ns->tx_bytes;

		stats->tx_packets = ns->tx_packets;

		stats->tx_dropped = ns->tx_dropped;

	} while (u64_stats_fetch_retry(&ns->syncp, start));

}
@@ -302,7 +320,6 @@ 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;

drivers/net/netdevsim/netdevsim.h

+1 −0
Original line number Diff line number Diff line
@@ -98,6 +98,7 @@ struct netdevsim { 


	u64 tx_packets;

	u64 tx_bytes;

	u64 tx_dropped;

	struct u64_stats_sync syncp;



	struct nsim_bus_dev *nsim_bus_dev;