[PATCH v3 2/5] gso: add TCP/IPv4 GSO support

[Jiayu Hu <jiayu.hu@intel.com>]

This patch adds GSO support for TCP/IPv4 packets. Supported packets
may include a single VLAN tag. TCP/IPv4 GSO assumes that all input
packets have correct checksums, and doesn't update checksums for output
packets (the responsibility for this lies with the application).
Additionally, TCP/IPv4 GSO doesn't process IP fragmented packets.

TCP/IPv4 GSO uses two chained MBUFs, one direct MBUF and one indrect
MBUF, to organize an output packet. Note that we refer to these two
chained MBUFs as a two-segment MBUF. The direct MBUF stores the packet
header, while the indirect mbuf simply points to a location within the
original packet's payload. Consequently, use of the GSO library requires
multi-segment MBUF support in the TX functions of the NIC driver.

If a packet is GSOed, TCP/IPv4 GSO reduces its MBUF refcnt by 1. As a
result, when all of its GSOed segments are freed, the packet is freed
automatically.

Signed-off-by: Jiayu Hu <jiayu.hu@intel.com>
Signed-off-by: Mark Kavanagh <mark.b.kavanagh@intel.com>
---
 lib/librte_eal/common/include/rte_log.h |   1 +
 lib/librte_gso/Makefile                 |   2 +
 lib/librte_gso/gso_common.c             | 202 ++++++++++++++++++++++++++++++++
 lib/librte_gso/gso_common.h             | 113 ++++++++++++++++++
 lib/librte_gso/gso_tcp4.c               |  83 +++++++++++++
 lib/librte_gso/gso_tcp4.h               |  76 ++++++++++++
 lib/librte_gso/rte_gso.c                |  41 ++++++-
 7 files changed, 515 insertions(+), 3 deletions(-)
 create mode 100644 lib/librte_gso/gso_common.c
 create mode 100644 lib/librte_gso/gso_common.h
 create mode 100644 lib/librte_gso/gso_tcp4.c
 create mode 100644 lib/librte_gso/gso_tcp4.h

diff --git a/lib/librte_eal/common/include/rte_log.h b/lib/librte_eal/common/include/rte_log.h
index ec8dba7..2fa1199 100644
--- a/lib/librte_eal/common/include/rte_log.h
+++ b/lib/librte_eal/common/include/rte_log.h
@@ -87,6 +87,7 @@ extern struct rte_logs rte_logs;
 #define RTE_LOGTYPE_CRYPTODEV 17 /**< Log related to cryptodev. */
 #define RTE_LOGTYPE_EFD       18 /**< Log related to EFD. */
 #define RTE_LOGTYPE_EVENTDEV  19 /**< Log related to eventdev. */
+#define RTE_LOGTYPE_GSO       20 /**< Log related to GSO. */
 
 /* these log types can be used in an application */
 #define RTE_LOGTYPE_USER1     24 /**< User-defined log type 1. */
diff --git a/lib/librte_gso/Makefile b/lib/librte_gso/Makefile
index aeaacbc..2be64d1 100644
--- a/lib/librte_gso/Makefile
+++ b/lib/librte_gso/Makefile
@@ -42,6 +42,8 @@ LIBABIVER := 1
 
 #source files
 SRCS-$(CONFIG_RTE_LIBRTE_GSO) += rte_gso.c
+SRCS-$(CONFIG_RTE_LIBRTE_GSO) += gso_common.c
+SRCS-$(CONFIG_RTE_LIBRTE_GSO) += gso_tcp4.c
 
 # install this header file
 SYMLINK-$(CONFIG_RTE_LIBRTE_GSO)-include += rte_gso.h
diff --git a/lib/librte_gso/gso_common.c b/lib/librte_gso/gso_common.c
new file mode 100644
index 0000000..7c32e03
--- /dev/null
+++ b/lib/librte_gso/gso_common.c
@@ -0,0 +1,202 @@
+/*-
+ *   BSD LICENSE
+ *
+ *   Copyright(c) 2017 Intel Corporation. All rights reserved.
+ *   All rights reserved.
+ *
+ *   Redistribution and use in source and binary forms, with or without
+ *   modification, are permitted provided that the following conditions
+ *   are met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in
+ *       the documentation and/or other materials provided with the
+ *       distribution.
+ *     * Neither the name of Intel Corporation nor the names of its
+ *       contributors may be used to endorse or promote products derived
+ *       from this software without specific prior written permission.
+ *
+ *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ *   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ *   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ *   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ *   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <stdbool.h>
+#include <errno.h>
+
+#include <rte_memcpy.h>
+#include <rte_mempool.h>
+#include <rte_ether.h>
+#include <rte_ip.h>
+#include <rte_tcp.h>
+
+#include "gso_common.h"
+
+static inline void
+hdr_segment_init(struct rte_mbuf *hdr_segment, struct rte_mbuf *pkt,
+		uint16_t pkt_hdr_offset)
+{
+	/* Copy MBUF metadata */
+	hdr_segment->nb_segs = 1;
+	hdr_segment->port = pkt->port;
+	hdr_segment->ol_flags = pkt->ol_flags;
+	hdr_segment->packet_type = pkt->packet_type;
+	hdr_segment->pkt_len = pkt_hdr_offset;
+	hdr_segment->data_len = pkt_hdr_offset;
+	hdr_segment->tx_offload = pkt->tx_offload;
+
+	/* Copy the packet header */
+	rte_memcpy(rte_pktmbuf_mtod(hdr_segment, char *),
+			rte_pktmbuf_mtod(pkt, char *),
+			pkt_hdr_offset);
+}
+
+static inline void
+free_gso_segment(struct rte_mbuf **pkts, uint16_t nb_pkts)
+{
+	uint16_t i;
+
+	for (i = 0; i < nb_pkts; i++)
+		rte_pktmbuf_free(pkts[i]);
+}
+
+int
+gso_do_segment(struct rte_mbuf *pkt,
+		uint16_t pkt_hdr_offset,
+		uint16_t pyld_unit_size,
+		struct rte_mempool *direct_pool,
+		struct rte_mempool *indirect_pool,
+		struct rte_mbuf **pkts_out,
+		uint16_t nb_pkts_out)
+{
+	struct rte_mbuf *pkt_in;
+	struct rte_mbuf *hdr_segment, *pyld_segment, *prev_segment;
+	uint16_t pkt_in_data_pos, segment_bytes_remaining;
+	uint16_t pyld_len, nb_segs;
+	bool more_in_pkt, more_out_segs;
+
+	pkt_in = pkt;
+	nb_segs = 0;
+	more_in_pkt = 1;
+	pkt_in_data_pos = pkt_hdr_offset;
+
+	while (more_in_pkt) {
+		if (unlikely(nb_segs >= nb_pkts_out)) {
+			free_gso_segment(pkts_out, nb_segs);
+			return -EINVAL;
+		}
+
+		/* Allocate a direct MBUF */
+		hdr_segment = rte_pktmbuf_alloc(direct_pool);
+		if (unlikely(hdr_segment == NULL)) {
+			free_gso_segment(pkts_out, nb_segs);
+			return -ENOMEM;
+		}
+		/* Fill the packet header */
+		hdr_segment_init(hdr_segment, pkt, pkt_hdr_offset);
+
+		prev_segment = hdr_segment;
+		segment_bytes_remaining = pyld_unit_size;
+		more_out_segs = 1;
+
+		while (more_out_segs && more_in_pkt) {
+			/* Allocate an indirect MBUF */
+			pyld_segment = rte_pktmbuf_alloc(indirect_pool);
+			if (unlikely(pyld_segment == NULL)) {
+				rte_pktmbuf_free(hdr_segment);
+				free_gso_segment(pkts_out, nb_segs);
+				return -ENOMEM;
+			}
+			/* Attach to current MBUF segment of pkt */
+			rte_pktmbuf_attach(pyld_segment, pkt_in);
+
+			prev_segment->next = pyld_segment;
+			prev_segment = pyld_segment;
+
+			pyld_len = segment_bytes_remaining;
+			if (pyld_len + pkt_in_data_pos > pkt_in->data_len)
+				pyld_len = pkt_in->data_len - pkt_in_data_pos;
+
+			pyld_segment->data_off = pkt_in_data_pos +
+				pkt_in->data_off;
+			pyld_segment->data_len = pyld_len;
+
+			/* Update header segment */
+			hdr_segment->pkt_len += pyld_len;
+			hdr_segment->nb_segs++;
+
+			pkt_in_data_pos += pyld_len;
+			segment_bytes_remaining -= pyld_len;
+
+			/* Finish processing a MBUF segment of pkt */
+			if (pkt_in_data_pos == pkt_in->data_len) {
+				pkt_in = pkt_in->next;
+				pkt_in_data_pos = 0;
+				if (pkt_in == NULL)
+					more_in_pkt = 0;
+			}
+
+			/* Finish generating a GSO segment */
+			if (segment_bytes_remaining == 0)
+				more_out_segs = 0;
+		}
+		pkts_out[nb_segs++] = hdr_segment;
+	}
+	return nb_segs;
+}
+
+static inline void
+update_inner_tcp4_header(struct rte_mbuf *pkt, uint8_t ipid_delta,
+		struct rte_mbuf **segs, uint16_t nb_segs)
+{
+	struct tcp_hdr *tcp_hdr;
+	struct ipv4_hdr *ipv4_hdr;
+	struct rte_mbuf *seg;
+	uint32_t sent_seq;
+	uint16_t inner_l2_offset;
+	uint16_t id, i;
+
+	inner_l2_offset = pkt->outer_l2_len + pkt->outer_l3_len + pkt->l2_len;
+	ipv4_hdr = (struct ipv4_hdr *)(rte_pktmbuf_mtod(pkt, char *) +
+			inner_l2_offset);
+	tcp_hdr = (struct tcp_hdr *)((char *)ipv4_hdr + pkt->l3_len);
+	id = rte_be_to_cpu_16(ipv4_hdr->packet_id);
+	sent_seq = rte_be_to_cpu_32(tcp_hdr->sent_seq);
+
+	for (i = 0; i < nb_segs; i++) {
+		seg = segs[i];
+		/* Update the inner IPv4 header */
+		ipv4_hdr = (struct ipv4_hdr *)(rte_pktmbuf_mtod(seg, char *) +
+				inner_l2_offset);
+		ipv4_hdr->total_length = rte_cpu_to_be_16(seg->pkt_len -
+				inner_l2_offset);
+		ipv4_hdr->packet_id = rte_cpu_to_be_16(id);
+		id += ipid_delta;
+
+		/* Update the inner TCP header */
+		tcp_hdr = (struct tcp_hdr *)((char *)ipv4_hdr + seg->l3_len);
+		tcp_hdr->sent_seq = rte_cpu_to_be_32(sent_seq);
+		if (likely(i < nb_segs - 1))
+			tcp_hdr->tcp_flags &= (~(TCP_HDR_PSH_MASK |
+						TCP_HDR_FIN_MASK));
+		sent_seq += (seg->pkt_len - seg->data_len);
+	}
+}
+
+void
+gso_update_pkt_headers(struct rte_mbuf *pkt, uint8_t ipid_delta,
+		struct rte_mbuf **segs, uint16_t nb_segs)
+{
+	if (is_ipv4_tcp(pkt->packet_type))
+		update_inner_tcp4_header(pkt, ipid_delta, segs, nb_segs);
+}
diff --git a/lib/librte_gso/gso_common.h b/lib/librte_gso/gso_common.h
new file mode 100644
index 0000000..3c76520
--- /dev/null
+++ b/lib/librte_gso/gso_common.h
@@ -0,0 +1,113 @@
+/*-
+ *   BSD LICENSE
+ *
+ *   Copyright(c) 2017 Intel Corporation. All rights reserved.
+ *   All rights reserved.
+ *
+ *   Redistribution and use in source and binary forms, with or without
+ *   modification, are permitted provided that the following conditions
+ *   are met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in
+ *       the documentation and/or other materials provided with the
+ *       distribution.
+ *     * Neither the name of Intel Corporation nor the names of its
+ *       contributors may be used to endorse or promote products derived
+ *       from this software without specific prior written permission.
+ *
+ *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ *   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ *   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ *   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ *   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _GSO_COMMON_H_
+#define _GSO_COMMON_H_
+
+#include <stdint.h>
+#include <rte_mbuf.h>
+
+#define IPV4_HDR_DF_SHIFT 14
+#define IPV4_HDR_DF_MASK (1 << IPV4_HDR_DF_SHIFT)
+
+#define TCP_HDR_PSH_MASK ((uint8_t)0x08)
+#define TCP_HDR_FIN_MASK ((uint8_t)0x01)
+
+#define ETHER_TCP_PKT (RTE_PTYPE_L2_ETHER | RTE_PTYPE_L4_TCP)
+#define ETHER_VLAN_TCP_PKT (RTE_PTYPE_L2_ETHER_VLAN | RTE_PTYPE_L4_TCP)
+static inline uint8_t is_ipv4_tcp(uint32_t ptype)
+{
+	switch (ptype & (~RTE_PTYPE_L3_MASK)) {
+	case ETHER_VLAN_TCP_PKT:
+	case ETHER_TCP_PKT:
+		return RTE_ETH_IS_IPV4_HDR(ptype);
+	default:
+		return 0;
+	}
+}
+
+/**
+ * Internal function which updates relevant packet headers, following
+ * segmentation. This is required to update, for example, the IPv4
+ * 'total_length' field, to reflect the reduced length of the now-
+ * segmented packet.
+ *
+ * @param pkt
+ *  The original packet.
+ * @param ipid_delta
+ *  The increasing uint of IP ids.
+ * @param segs
+ *  Pointer array used for storing mbuf addresses for GSO segments.
+ * @param nb_segs
+ *  The number of GSO segments placed in segs.
+ */
+void gso_update_pkt_headers(struct rte_mbuf *pkt, uint8_t ipid_delta,
+		struct rte_mbuf **segs, uint16_t nb_segs);
+
+/**
+ * Internal function which divides the input packet into small segments.
+ * Each of the newly-created segments is organized as a two-segment MBUF,
+ * where the first segment is a standard mbuf, which stores a copy of
+ * packet header, and the second is an indirect mbuf which points to a
+ * section of data in the input packet.
+ *
+ * @param pkt
+ *  Packet to segment.
+ * @param pkt_hdr_offset
+ *  Packet header offset, measured in bytes.
+ * @param pyld_unit_size
+ *  The max payload length of a GSO segment.
+ * @param direct_pool
+ *  MBUF pool used for allocating direct buffers for output segments.
+ * @param indirect_pool
+ *  MBUF pool used for allocating indirect buffers for output segments.
+ * @param pkts_out
+ *  Pointer array used to keep the mbuf addresses of output segments. If
+ *  the memory space in pkts_out is insufficient, gso_do_segment() fails
+ *  and returns -EINVAL.
+ * @param nb_pkts_out
+ *  The max number of items that pkts_out can keep.
+ *
+ * @return
+ *  - The number of segments created in the event of success.
+ *  - Return -ENOMEM if run out of memory in MBUF pools.
+ *  - Return -EINVAL for invalid parameters.
+ */
+int gso_do_segment(struct rte_mbuf *pkt,
+		uint16_t pkt_hdr_offset,
+		uint16_t pyld_unit_size,
+		struct rte_mempool *direct_pool,
+		struct rte_mempool *indirect_pool,
+		struct rte_mbuf **pkts_out,
+		uint16_t nb_pkts_out);
+#endif
diff --git a/lib/librte_gso/gso_tcp4.c b/lib/librte_gso/gso_tcp4.c
new file mode 100644
index 0000000..8d4bfb2
--- /dev/null
+++ b/lib/librte_gso/gso_tcp4.c
@@ -0,0 +1,83 @@
+/*-
+ *   BSD LICENSE
+ *
+ *   Copyright(c) 2017 Intel Corporation. All rights reserved.
+ *   All rights reserved.
+ *
+ *   Redistribution and use in source and binary forms, with or without
+ *   modification, are permitted provided that the following conditions
+ *   are met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in
+ *       the documentation and/or other materials provided with the
+ *       distribution.
+ *     * Neither the name of Intel Corporation nor the names of its
+ *       contributors may be used to endorse or promote products derived
+ *       from this software without specific prior written permission.
+ *
+ *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ *   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ *   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ *   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ *   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+
+#include <rte_ether.h>
+#include <rte_ip.h>
+
+#include "gso_common.h"
+#include "gso_tcp4.h"
+
+int
+gso_tcp4_segment(struct rte_mbuf *pkt,
+		uint16_t gso_size,
+		uint8_t ipid_delta,
+		struct rte_mempool *direct_pool,
+		struct rte_mempool *indirect_pool,
+		struct rte_mbuf **pkts_out,
+		uint16_t nb_pkts_out)
+{
+	struct ipv4_hdr *ipv4_hdr;
+	uint16_t tcp_dl;
+	uint16_t pyld_unit_size;
+	uint16_t hdr_offset;
+	int ret = 1;
+
+	ipv4_hdr = (struct ipv4_hdr *)(rte_pktmbuf_mtod(pkt, char *) +
+			pkt->l2_len);
+	/* Don't process the fragmented packet */
+	if (unlikely((ipv4_hdr->fragment_offset & rte_cpu_to_be_16(
+						IPV4_HDR_DF_MASK)) == 0)) {
+		pkts_out[0] = pkt;
+		return ret;
+	}
+
+	tcp_dl = rte_be_to_cpu_16(ipv4_hdr->total_length) - pkt->l3_len -
+		pkt->l4_len;
+	/* Don't process the packet without data */
+	if (unlikely(tcp_dl == 0)) {
+		pkts_out[0] = pkt;
+		return ret;
+	}
+
+	hdr_offset = pkt->l2_len + pkt->l3_len + pkt->l4_len;
+	pyld_unit_size = gso_size - hdr_offset - ETHER_CRC_LEN;
+
+	/* Segment the payload */
+	ret = gso_do_segment(pkt, hdr_offset, pyld_unit_size, direct_pool,
+			indirect_pool, pkts_out, nb_pkts_out);
+	if (ret > 1)
+		gso_update_pkt_headers(pkt, ipid_delta, pkts_out, ret);
+
+	return ret;
+}
diff --git a/lib/librte_gso/gso_tcp4.h b/lib/librte_gso/gso_tcp4.h
new file mode 100644
index 0000000..9c07984
--- /dev/null
+++ b/lib/librte_gso/gso_tcp4.h
@@ -0,0 +1,76 @@
+/*-
+ *   BSD LICENSE
+ *
+ *   Copyright(c) 2017 Intel Corporation. All rights reserved.
+ *   All rights reserved.
+ *
+ *   Redistribution and use in source and binary forms, with or without
+ *   modification, are permitted provided that the following conditions
+ *   are met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in
+ *       the documentation and/or other materials provided with the
+ *       distribution.
+ *     * Neither the name of Intel Corporation nor the names of its
+ *       contributors may be used to endorse or promote products derived
+ *       from this software without specific prior written permission.
+ *
+ *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ *   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ *   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ *   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ *   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _GSO_TCP4_H_
+#define _GSO_TCP4_H_
+
+#include <stdint.h>
+#include <rte_mbuf.h>
+
+/**
+ * Segment an IPv4/TCP packet. This function assumes the input packet has
+ * correct checksums and doesn't update checksums for GSO segment.
+ * Furthermore, it doesn't process IP fragment packets.
+ *
+ * @param pkt
+ *  The packet mbuf to segment.
+ * @param gso_size
+ *  The max length of a GSO segment, measured in bytes.
+ * @param ipid_delta
+ *  The increasing uint of IP ids.
+ * @param direct_pool
+ *  MBUF pool used for allocating direct buffers for output segments.
+ * @param indirect_pool
+ *  MBUF pool used for allocating indirect buffers for output segments.
+ * @param pkts_out
+ *  Pointer array used to store the MBUF addresses of output GSO
+ *  segments, when gso_tcp4_segment() successes. If the memory space in
+ *  pkts_out is insufficient, gso_tcp4_segment() fails and returns
+ *  -EINVAL.
+ * @param nb_pkts_out
+ *  The max number of items that 'pkts_out' can keep.
+ *
+ * @return
+ *   - The number of GSO segments filled in pkts_out on success.
+ *   - Return -ENOMEM if run out of memory in MBUF pools.
+ *   - Return -EINVAL for invalid parameters.
+ */
+int gso_tcp4_segment(struct rte_mbuf *pkt,
+		uint16_t gso_size,
+		uint8_t ip_delta,
+		struct rte_mempool *direct_pool,
+		struct rte_mempool *indirect_pool,
+		struct rte_mbuf **pkts_out,
+		uint16_t nb_pkts_out);
+
+#endif
diff --git a/lib/librte_gso/rte_gso.c b/lib/librte_gso/rte_gso.c
index dda50ee..95f6ea6 100644
--- a/lib/librte_gso/rte_gso.c
+++ b/lib/librte_gso/rte_gso.c
@@ -33,18 +33,53 @@
 
 #include <errno.h>
 
+#include <rte_log.h>
+
 #include "rte_gso.h"
+#include "gso_common.h"
+#include "gso_tcp4.h"
 
 int
 rte_gso_segment(struct rte_mbuf *pkt,
-		struct rte_gso_ctx gso_ctx __rte_unused,
+		struct rte_gso_ctx gso_ctx,
 		struct rte_mbuf **pkts_out,
 		uint16_t nb_pkts_out)
 {
+	struct rte_mempool *direct_pool, *indirect_pool;
+	struct rte_mbuf *pkt_seg;
+	uint16_t gso_size;
+	uint8_t ipid_delta;
+	int ret = 1;
+
 	if (pkt == NULL || pkts_out == NULL || nb_pkts_out < 1)
 		return -EINVAL;
 
-	pkts_out[0] = pkt;
+	if (gso_ctx.gso_size >= pkt->pkt_len ||
+			(pkt->packet_type & gso_ctx.gso_types) !=
+			pkt->packet_type) {
+		pkts_out[0] = pkt;
+		return ret;
+	}
+
+	direct_pool = gso_ctx.direct_pool;
+	indirect_pool = gso_ctx.indirect_pool;
+	gso_size = gso_ctx.gso_size;
+	ipid_delta = gso_ctx.ipid_flag == RTE_GSO_IPID_INCREASE;
+
+	if (is_ipv4_tcp(pkt->packet_type)) {
+		ret = gso_tcp4_segment(pkt, gso_size, ipid_delta,
+				direct_pool, indirect_pool,
+				pkts_out, nb_pkts_out);
+	} else
+		RTE_LOG(WARNING, GSO, "Unsupported packet type\n");
+
+	if (ret > 1) {
+		pkt_seg = pkt;
+		while (pkt_seg) {
+			rte_mbuf_refcnt_update(pkt_seg, -1);
+			pkt_seg = pkt_seg->next;
+		}
+	}
 
-	return 1;
+	return ret;
 }
-- 
2.7.4