[net-next v5 11/12] net: netdevsim: Add support for SW USO

[Joe Damato <joe@dama.to>]

Add support for UDP Segmentation Offloading in software (SW USO). This
is helpful for testing when real hardware is not available. A test which
uses this codepath will be added in a following commit.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Joe Damato <joe@dama.to>
---
 v5:
   - Added Pavan's Reviewed-by. No functional changes.

 v4:
   - Added parentheses around the gso_type check for clarity. No functional
     change.

 rfcv2:
   - new in rfcv2

 drivers/net/netdevsim/netdev.c | 100 ++++++++++++++++++++++++++++++++-
 1 file changed, 99 insertions(+), 1 deletion(-)

diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index c71b8d116f18..f228bcf3d190 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -30,6 +30,7 @@
 #include <net/rtnetlink.h>
 #include <net/udp_tunnel.h>
 #include <net/busy_poll.h>
+#include <net/tso.h>
 
 #include "netdevsim.h"
 
@@ -120,6 +121,98 @@ static int nsim_forward_skb(struct net_device *tx_dev,
 	return nsim_napi_rx(tx_dev, rx_dev, rq, skb);
 }
 
+static netdev_tx_t nsim_uso_segment_xmit(struct net_device *dev,
+					 struct sk_buff *skb)
+{
+	unsigned int hdr_len, mss, total_payload, num_segs;
+	struct netdevsim *ns = netdev_priv(dev);
+	struct net_device *peer_dev;
+	unsigned int total_len = 0;
+	struct netdevsim *peer_ns;
+	struct nsim_rq *rq;
+	struct tso_t tso;
+	int i, rxq;
+
+	hdr_len = tso_start(skb, &tso);
+	mss = skb_shinfo(skb)->gso_size;
+	total_payload = skb->len - hdr_len;
+	num_segs = DIV_ROUND_UP(total_payload, mss);
+
+	udp_hdr(skb)->check = 0;
+	if (!tso.ipv6)
+		ip_hdr(skb)->check = 0;
+
+	rcu_read_lock();
+	peer_ns = rcu_dereference(ns->peer);
+	if (!peer_ns)
+		goto out_drop_free;
+
+	peer_dev = peer_ns->netdev;
+	rxq = skb_get_queue_mapping(skb);
+	if (rxq >= peer_dev->num_rx_queues)
+		rxq = rxq % peer_dev->num_rx_queues;
+	rq = peer_ns->rq[rxq];
+
+	for (i = 0; i < num_segs; i++) {
+		unsigned int seg_payload = min_t(unsigned int, mss,
+						 total_payload);
+		bool last = (i == num_segs - 1);
+		unsigned int seg_remaining;
+		struct sk_buff *seg;
+
+		seg = alloc_skb(hdr_len + seg_payload, GFP_ATOMIC);
+		if (!seg)
+			break;
+
+		seg->dev = dev;
+
+		tso_build_hdr(skb, skb_put(seg, hdr_len), &tso,
+			      seg_payload, last);
+
+		if (!tso.ipv6) {
+			unsigned int nh_off = skb_network_offset(skb);
+			struct iphdr *iph;
+
+			iph = (struct iphdr *)(seg->data + nh_off);
+			iph->check = ip_fast_csum(iph, iph->ihl);
+		}
+
+		seg_remaining = seg_payload;
+		while (seg_remaining > 0) {
+			unsigned int chunk = min_t(unsigned int, tso.size,
+						   seg_remaining);
+
+			memcpy(skb_put(seg, chunk), tso.data, chunk);
+			tso_build_data(skb, &tso, chunk);
+			seg_remaining -= chunk;
+		}
+
+		total_payload -= seg_payload;
+
+		seg->ip_summed = CHECKSUM_UNNECESSARY;
+
+		if (nsim_forward_skb(dev, peer_dev, seg, rq, NULL) == NET_RX_DROP)
+			continue;
+
+		total_len += hdr_len + seg_payload;
+	}
+
+	if (!hrtimer_active(&rq->napi_timer))
+		hrtimer_start(&rq->napi_timer, us_to_ktime(5),
+			      HRTIMER_MODE_REL);
+
+	rcu_read_unlock();
+	dev_kfree_skb(skb);
+	dev_dstats_tx_add(dev, total_len);
+	return NETDEV_TX_OK;
+
+out_drop_free:
+	dev_kfree_skb(skb);
+	rcu_read_unlock();
+	dev_dstats_tx_dropped(dev);
+	return NETDEV_TX_OK;
+}
+
 static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct netdevsim *ns = netdev_priv(dev);
@@ -132,6 +225,10 @@ static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	int rxq;
 	int dr;
 
+	if (skb_is_gso(skb) &&
+	    skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
+		return nsim_uso_segment_xmit(dev, skb);
+
 	rcu_read_lock();
 	if (!nsim_ipsec_tx(ns, skb))
 		goto out_drop_any;
@@ -938,7 +1035,8 @@ static void nsim_setup(struct net_device *dev)
 			    NETIF_F_HW_CSUM |
 			    NETIF_F_LRO |
 			    NETIF_F_TSO |
-			    NETIF_F_LOOPBACK;
+			    NETIF_F_LOOPBACK |
+			    NETIF_F_GSO_UDP_L4;
 	dev->pcpu_stat_type = NETDEV_PCPU_STAT_DSTATS;
 	dev->max_mtu = ETH_MAX_MTU;
 	dev->xdp_features = NETDEV_XDP_ACT_BASIC | NETDEV_XDP_ACT_HW_OFFLOAD;
-- 
2.52.0