[PATCH net-next v6 2/4] netdevsim: forward skbs from one connected port to another
From: David Wei <hidden>
Date: 2024-01-26 01:24:02
Subsystem:
netdevsim, networking drivers, the rest · Maintainers:
Jakub Kicinski, Andrew Lunn, "David S. Miller", Eric Dumazet, Paolo Abeni, Linus Torvalds
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 rtnl_lock, making it safe with concurrent calls to linking two netdevsims together. Signed-off-by: David Wei <redacted> --- drivers/net/netdevsim/netdev.c | 24 ++++++++++++++++++++---- drivers/net/netdevsim/netdevsim.h | 1 + 2 files changed, 21 insertions(+), 4 deletions(-)
diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index 969248ffeca8..978c34334018 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c@@ -29,19 +29,35 @@ 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; + unsigned int len = skb->len; + int ret = NETDEV_TX_OK; if (!nsim_ipsec_tx(ns, skb)) goto out; + rcu_read_lock(); + peer_ns = rcu_dereference(ns->peer); + if (!peer_ns) + goto out_stats; + + skb_tx_timestamp(skb); + if (unlikely(dev_forward_skb(peer_ns->netdev, skb) == NET_RX_DROP)) + ret = NET_XMIT_DROP; + +out_stats: + rcu_read_unlock(); u64_stats_update_begin(&ns->syncp); ns->tx_packets++; - ns->tx_bytes += skb->len; + ns->tx_bytes += len; + if (ret == NET_XMIT_DROP) + ns->tx_dropped++; u64_stats_update_end(&ns->syncp); + return ret; out: dev_kfree_skb(skb); - - return NETDEV_TX_OK; + return ret; } static void nsim_set_rx_mode(struct net_device *dev)
@@ -70,6 +86,7 @@ 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 +319,6 @@ 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;
diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h
index c8b45b0d955e..553c4b9b4f63 100644
--- a/drivers/net/netdevsim/netdevsim.h
+++ b/drivers/net/netdevsim/netdevsim.h@@ -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;
--
2.39.3