ethtool: add SET for TCP_DATA_SPLIT ringparam

Follow up commit 9690ae60 ("ethtool: add header/data split
indication") and add the set part of Ethtool's header split, i.e.
ability to enable/disable header split via the Ethtool Netlink
interface. This might be helpful to optimize the setup for particular
workloads, for example, to avoid XDP frags, and so on.
A driver should advertise ``ETHTOOL_RING_USE_TCP_DATA_SPLIT`` in its
ops->supported_ring_params to allow doing that. "Unknown" passed from
the userspace when the header split is supported means the driver is
free to choose the preferred state.
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Link: https://lore.kernel.org/r/20231212142752.935000-2-aleksander.lobakin@intel.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/ethtool.h

@@ -95,6 +95,7 @@ struct kernel_ethtool_ringparam {
  * @ETHTOOL_RING_USE_TX_PUSH: capture for setting tx_push
  * @ETHTOOL_RING_USE_RX_PUSH: capture for setting rx_push
  * @ETHTOOL_RING_USE_TX_PUSH_BUF_LEN: capture for setting tx_push_buf_len
+ * @ETHTOOL_RING_USE_TCP_DATA_SPLIT: capture for setting tcp_data_split
  */
 enum ethtool_supported_ring_param {
 	ETHTOOL_RING_USE_RX_BUF_LEN		= BIT(0),
@@ -102,6 +103,7 @@ enum ethtool_supported_ring_param {
 	ETHTOOL_RING_USE_TX_PUSH		= BIT(2),
 	ETHTOOL_RING_USE_RX_PUSH		= BIT(3),
 	ETHTOOL_RING_USE_TX_PUSH_BUF_LEN	= BIT(4),
+	ETHTOOL_RING_USE_TCP_DATA_SPLIT		= BIT(5),
 };
 
 #define __ETH_RSS_HASH_BIT(bit)	((u32)1 << (bit))

net/ethtool/rings.c

@@ -124,6 +124,8 @@ const struct nla_policy ethnl_rings_set_policy[] = {
 	[ETHTOOL_A_RINGS_RX_JUMBO]		= { .type = NLA_U32 },
 	[ETHTOOL_A_RINGS_TX]			= { .type = NLA_U32 },
 	[ETHTOOL_A_RINGS_RX_BUF_LEN]            = NLA_POLICY_MIN(NLA_U32, 1),
+	[ETHTOOL_A_RINGS_TCP_DATA_SPLIT]	=
+		NLA_POLICY_MAX(NLA_U8, ETHTOOL_TCP_DATA_SPLIT_ENABLED),
 	[ETHTOOL_A_RINGS_CQE_SIZE]		= NLA_POLICY_MIN(NLA_U32, 1),
 	[ETHTOOL_A_RINGS_TX_PUSH]		= NLA_POLICY_MAX(NLA_U8, 1),
 	[ETHTOOL_A_RINGS_RX_PUSH]		= NLA_POLICY_MAX(NLA_U8, 1),
@@ -145,6 +147,14 @@ ethnl_set_rings_validate(struct ethnl_req_info *req_info,
 		return -EOPNOTSUPP;
 	}
 
+	if (tb[ETHTOOL_A_RINGS_TCP_DATA_SPLIT] &&
+	    !(ops->supported_ring_params & ETHTOOL_RING_USE_TCP_DATA_SPLIT)) {
+		NL_SET_ERR_MSG_ATTR(info->extack,
+				    tb[ETHTOOL_A_RINGS_TCP_DATA_SPLIT],
+				    "setting TCP data split is not supported");
+		return -EOPNOTSUPP;
+	}
+
 	if (tb[ETHTOOL_A_RINGS_CQE_SIZE] &&
 	    !(ops->supported_ring_params & ETHTOOL_RING_USE_CQE_SIZE)) {
 		NL_SET_ERR_MSG_ATTR(info->extack,
@@ -202,6 +212,8 @@ ethnl_set_rings(struct ethnl_req_info *req_info, struct genl_info *info)
 	ethnl_update_u32(&ringparam.tx_pending, tb[ETHTOOL_A_RINGS_TX], &mod);
 	ethnl_update_u32(&kernel_ringparam.rx_buf_len,
 			 tb[ETHTOOL_A_RINGS_RX_BUF_LEN], &mod);
+	ethnl_update_u8(&kernel_ringparam.tcp_data_split,
+			tb[ETHTOOL_A_RINGS_TCP_DATA_SPLIT], &mod);
 	ethnl_update_u32(&kernel_ringparam.cqe_size,
 			 tb[ETHTOOL_A_RINGS_CQE_SIZE], &mod);
 	ethnl_update_u8(&kernel_ringparam.tx_push,