[PATCH v5 06/10] net/rtap: add checksum and TSO offload support

[Stephen Hemminger <stephen@networkplumber.org>]

Add transmit and receive offload support using the virtio-net header
that is exchanged with the kernel TAP device.

Tx offloads:
  - UDP and TCP checksum offload: set VIRTIO_NET_HDR_F_NEEDS_CSUM
    with appropriate csum_start and csum_offset fields
  - TCP segmentation offload (TSO): set gso_type and gso_size

Rx offloads:
  - Parse virtio-net header flags to determine checksum status
  - Handle NEEDS_CSUM by either marking L4_CKSUM_NONE for known
    protocols or computing the checksum in software for tunnels
  - Handle DATA_VALID flag to mark L4_CKSUM_GOOD
  - Parse GSO headers to populate LRO metadata

Configure kernel-side offloads via TUNSETOFFLOAD in dev_configure
based on the requested rx offload flags.

Report offload capabilities in dev_info.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 doc/guides/nics/features/rtap.ini |  2 ++
 drivers/net/rtap/rtap_ethdev.c    | 30 +++++++++++++++++++++++++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/doc/guides/nics/features/rtap.ini b/doc/guides/nics/features/rtap.ini
index ce0804d795..b8eaa805fe 100644
--- a/doc/guides/nics/features/rtap.ini
+++ b/doc/guides/nics/features/rtap.ini
@@ -11,6 +11,8 @@ Allmulticast mode    = Y
 Scattered Rx         = P
 Basic stats          = Y
 Stats per queue      = Y
+TSO                  = Y
+L4 checksum offload  = Y
 Linux                = Y
 ARMv7                = Y
 ARMv8                = Y
diff --git a/drivers/net/rtap/rtap_ethdev.c b/drivers/net/rtap/rtap_ethdev.c
index 591fe91eac..277a280772 100644
--- a/drivers/net/rtap/rtap_ethdev.c
+++ b/drivers/net/rtap/rtap_ethdev.c
@@ -31,6 +31,16 @@
 
 #define RTAP_DEFAULT_IFNAME	"rtap%d"
 
+#define RTAP_TX_OFFLOAD		(RTE_ETH_TX_OFFLOAD_MULTI_SEGS | \
+				 RTE_ETH_TX_OFFLOAD_UDP_CKSUM | \
+				 RTE_ETH_TX_OFFLOAD_TCP_CKSUM | \
+				 RTE_ETH_TX_OFFLOAD_TCP_TSO)
+
+#define RTAP_RX_OFFLOAD		(RTE_ETH_RX_OFFLOAD_UDP_CKSUM | \
+				 RTE_ETH_RX_OFFLOAD_TCP_CKSUM | \
+				 RTE_ETH_RX_OFFLOAD_TCP_LRO | \
+				 RTE_ETH_RX_OFFLOAD_SCATTER)
+
 #define RTAP_DEFAULT_BURST	64
 #define RTAP_NUM_BUFFERS	1024
 #define RTAP_MAX_QUEUES		128
@@ -317,7 +327,21 @@ rtap_dev_configure(struct rte_eth_dev *dev)
 	if (dev->data->nb_rx_queues != dev->data->nb_tx_queues)
 		return -EINVAL;
 
-	if (ioctl(pmd->keep_fd, TUNSETOFFLOAD, 0) != 0) {
+	/*
+	 * Set offload flags visible on the kernel network interface.
+	 * This controls whether kernel will use checksum offload etc.
+	 * Note: kernel transmit is DPDK receive.
+	 */
+	const struct rte_eth_rxmode *rx_mode = &dev->data->dev_conf.rxmode;
+	unsigned int offload = 0;
+	if (rx_mode->offloads & RTE_ETH_RX_OFFLOAD_CHECKSUM) {
+		offload |= TUN_F_CSUM;
+
+		if (rx_mode->offloads & RTE_ETH_RX_OFFLOAD_TCP_LRO)
+			offload |= TUN_F_TSO4 | TUN_F_TSO6 | TUN_F_TSO_ECN;
+	}
+
+	if (ioctl(pmd->keep_fd, TUNSETOFFLOAD, offload) != 0) {
 		PMD_LOG(ERR, "ioctl(TUNSETOFFLOAD) failed: %s", strerror(errno));
 		return -1;
 	}
@@ -336,6 +360,10 @@ rtap_dev_info(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
 	dev_info->min_rx_bufsize = RTAP_MIN_RX_BUFSIZE;
 	dev_info->max_rx_queues = RTAP_MAX_QUEUES;
 	dev_info->max_tx_queues = RTAP_MAX_QUEUES;
+	dev_info->rx_queue_offload_capa = RTAP_RX_OFFLOAD;
+	dev_info->rx_offload_capa = dev_info->rx_queue_offload_capa;
+	dev_info->tx_queue_offload_capa = RTAP_TX_OFFLOAD;
+	dev_info->tx_offload_capa = dev_info->tx_queue_offload_capa;
 
 	dev_info->default_rxportconf = (struct rte_eth_dev_portconf) {
 		.burst_size = RTAP_DEFAULT_BURST,
-- 
2.51.0