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Message-Id: <20240127040354.944744-3-dw@davidwei.uk>
Date: Fri, 26 Jan 2024 20:03:52 -0800
From: David Wei <dw@...idwei.uk>
To: Jakub Kicinski <kuba@...nel.org>,
Jiri Pirko <jiri@...nulli.us>,
Sabrina Dubroca <sd@...asysnail.net>,
netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH net-next v7 2/4] 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: David Wei <dw@...idwei.uk>
---
drivers/net/netdevsim/netdev.c | 28 +++++++++++++++++++++++-----
drivers/net/netdevsim/netdevsim.h | 1 +
2 files changed, 24 insertions(+), 5 deletions(-)
diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index 969248ffeca8..120a24d74d28 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -29,19 +29,37 @@
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;
+ 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;
+ if (ret == NET_XMIT_DROP) {
+ ns->tx_dropped++;
+ } else {
+ ns->tx_packets++;
+ ns->tx_bytes += len;
+ }
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 +88,7 @@ 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 +321,6 @@ 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
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