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Miller" , Eric Dumazet , Paolo Abeni Cc: michael.chan@broadcom.com, pavan.chebbi@broadcom.com, linux-kernel@vger.kernel.org, Joe Damato Subject: [RFC net-next v2 11/12] net: netdevsim: Add support for SW USO Date: Thu, 12 Mar 2026 15:34:48 -0700 Message-ID: <20260312223457.1999489-12-joe@dama.to> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260312223457.1999489-1-joe@dama.to> References: <20260312223457.1999489-1-joe@dama.to> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 Signed-off-by: Joe Damato --- 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 5ec028a00c62..f7dd7692a5d9 100644 --- a/drivers/net/netdevsim/netdev.c +++ b/drivers/net/netdevsim/netdev.c @@ -30,6 +30,7 @@ #include #include #include +#include =20 #include "netdevsim.h" =20 @@ -117,6 +118,98 @@ static int nsim_forward_skb(struct net_device *tx_dev, return nsim_napi_rx(tx_dev, rx_dev, rq, skb); } =20 +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 =3D netdev_priv(dev); + struct net_device *peer_dev; + unsigned int total_len =3D 0; + struct netdevsim *peer_ns; + struct nsim_rq *rq; + struct tso_t tso; + int i, rxq; + + hdr_len =3D tso_start(skb, &tso); + mss =3D skb_shinfo(skb)->gso_size; + total_payload =3D skb->len - hdr_len; + num_segs =3D DIV_ROUND_UP(total_payload, mss); + + udp_hdr(skb)->check =3D 0; + if (!tso.ipv6) + ip_hdr(skb)->check =3D 0; + + rcu_read_lock(); + peer_ns =3D rcu_dereference(ns->peer); + if (!peer_ns) + goto out_drop_free; + + peer_dev =3D peer_ns->netdev; + rxq =3D skb_get_queue_mapping(skb); + if (rxq >=3D peer_dev->num_rx_queues) + rxq =3D rxq % peer_dev->num_rx_queues; + rq =3D peer_ns->rq[rxq]; + + for (i =3D 0; i < num_segs; i++) { + unsigned int seg_payload =3D min_t(unsigned int, mss, + total_payload); + bool last =3D (i =3D=3D num_segs - 1); + unsigned int seg_remaining; + struct sk_buff *seg; + + seg =3D alloc_skb(hdr_len + seg_payload, GFP_ATOMIC); + if (!seg) + break; + + seg->dev =3D dev; + + tso_build_hdr(skb, skb_put(seg, hdr_len), &tso, + seg_payload, last); + + if (!tso.ipv6) { + unsigned int nh_off =3D skb_network_offset(skb); + struct iphdr *iph; + + iph =3D (struct iphdr *)(seg->data + nh_off); + iph->check =3D ip_fast_csum(iph, iph->ihl); + } + + seg_remaining =3D seg_payload; + while (seg_remaining > 0) { + unsigned int chunk =3D min_t(unsigned int, tso.size, + seg_remaining); + + memcpy(skb_put(seg, chunk), tso.data, chunk); + tso_build_data(skb, &tso, chunk); + seg_remaining -=3D chunk; + } + + total_payload -=3D seg_payload; + + seg->ip_summed =3D CHECKSUM_UNNECESSARY; + + if (nsim_forward_skb(dev, peer_dev, seg, rq, NULL) =3D=3D NET_RX_DROP) + continue; + + total_len +=3D 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 =3D netdev_priv(dev); @@ -129,6 +222,10 @@ static netdev_tx_t nsim_start_xmit(struct sk_buff *skb= , struct net_device *dev) int rxq; int dr; =20 + 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; @@ -986,7 +1083,8 @@ 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 =3D NETDEV_PCPU_STAT_DSTATS; dev->max_mtu =3D ETH_MAX_MTU; dev->xdp_features =3D NETDEV_XDP_ACT_BASIC | NETDEV_XDP_ACT_HW_OFFLOAD; --=20 2.52.0