[dpdk-dev,2/2] doc: flow classify sample app guide
diff mbox

Message ID 1509008957-11812-3-git-send-email-bernard.iremonger@intel.com
State Superseded, archived
Headers show

Checks

Context Check Description
ci/checkpatch warning coding style issues
ci/Intel-compilation success Compilation OK

Commit Message

Bernard Iremonger Oct. 26, 2017, 9:09 a.m. UTC
This file documents the flow_classify sample application
which is used to demonstate use of the Flow Classify library,
librte_flow_classify.

Updated MAINTAINERS file

Signed-off-by: Bernard Iremonger <bernard.iremonger@intel.com>
---
 MAINTAINERS                                |   1 +
 doc/guides/sample_app_ug/flow_classify.rst | 592 +++++++++++++++++++++++++++++
 doc/guides/sample_app_ug/index.rst         |   1 +
 3 files changed, 594 insertions(+)
 create mode 100644 doc/guides/sample_app_ug/flow_classify.rst

Comments

Mcnamara, John Nov. 2, 2017, 5 p.m. UTC | #1
> -----Original Message-----
> From: Iremonger, Bernard
> Sent: Thursday, October 26, 2017 10:09 AM
> To: dev@dpdk.org; Mcnamara, John <john.mcnamara@intel.com>
> Cc: Iremonger, Bernard <bernard.iremonger@intel.com>
> Subject: [PATCH 2/2] doc: flow classify sample app guide
> 
> This file documents the flow_classify sample application which is used to
> demonstate use of the Flow Classify library, librte_flow_classify.
> 
> Updated MAINTAINERS file
> 
> Signed-off-by: Bernard Iremonger <bernard.iremonger@intel.com>

> +
> +Compiling the Application
> +-------------------------
> +
> +To compile the application export the path to the DPDK source tree and
> +go to the example directory:
> +


There is now a simple section for compilation that you can reference directly
like this:

http://dpdk.org/doc/guides/sample_app_ug/hello_world.html#compiling-the-application

Copy the example from one of the other sample app guides.


John
Bernard Iremonger Nov. 2, 2017, 5:32 p.m. UTC | #2
Hi John,

<snip>

> > Subject: [PATCH 2/2] doc: flow classify sample app guide
> >
> > This file documents the flow_classify sample application which is used
> > to demonstate use of the Flow Classify library, librte_flow_classify.
> >
> > Updated MAINTAINERS file
> >
> > Signed-off-by: Bernard Iremonger <bernard.iremonger@intel.com>
> 
> > +
> > +Compiling the Application
> > +-------------------------
> > +
> > +To compile the application export the path to the DPDK source tree
> > +and go to the example directory:
> > +
> 
> 
> There is now a simple section for compilation that you can reference directly
> like this:
> 
> http://dpdk.org/doc/guides/sample_app_ug/hello_world.html#compiling-
> the-application
> 
> Copy the example from one of the other sample app guides.

Will do.

> 
> 
> John

Regards,

Bernard.

Patch
diff mbox

diff --git a/MAINTAINERS b/MAINTAINERS
index 117d104..63ba5ab 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -719,6 +719,7 @@  F: lib/librte_flow_classify/
 F: test/test/test_flow_classify*
 F: examples/flow_classify/
 F: doc/guides/prog_guide/flow_classify_lib.rst
+F: doc/guides/sample_app_ug/flow_classify.rst
 
 Distributor
 M: Bruce Richardson <bruce.richardson@intel.com>
diff --git a/doc/guides/sample_app_ug/flow_classify.rst b/doc/guides/sample_app_ug/flow_classify.rst
new file mode 100644
index 0000000..b2f5e4f
--- /dev/null
+++ b/doc/guides/sample_app_ug/flow_classify.rst
@@ -0,0 +1,592 @@ 
+..  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.
+
+Flow Classify Sample Application
+================================
+
+The Flow Classify sample application is based on the simple *skeleton* example
+of a forwarding application.
+
+It is intended as a demonstration of the basic components of a DPDK forwarding
+application which uses the Flow Classify library API's.
+
+Please refer to the
+:doc:`../prog_guide/flow_classify_lib`
+for more information.
+
+Compiling the Application
+-------------------------
+
+To compile the application export the path to the DPDK source tree and go to
+the example directory:
+
+.. code-block:: console
+
+    export RTE_SDK=/path/to/rte_sdk
+
+    cd ${RTE_SDK}/examples/flow_classify
+
+Set the target, for example:
+
+.. code-block:: console
+
+    export RTE_TARGET=x86_64-native-linuxapp-gcc
+
+See the *DPDK Getting Started* Guide for possible ``RTE_TARGET`` values.
+
+Build the application as follows:
+
+.. code-block:: console
+
+    make clean
+
+    make
+
+Running the Application
+-----------------------
+
+To run the example in a ``linuxapp`` environment:
+
+.. code-block:: console
+
+    ./build/flow_classify -c 4 -n 4 -- --rule_ipv4="../ipv4_rules_file.txt"
+
+Refer to *DPDK Getting Started Guide* for general information on running
+applications and the Environment Abstraction Layer (EAL) options.
+
+Sample ipv4_rules_file.txt
+--------------------------
+
+.. code-block:: console
+
+    #file format:
+    #src_ip/masklen dst_ip/masklen src_port : mask dst_port : mask proto/mask priority
+    #
+    2.2.2.3/24 2.2.2.7/24 32 : 0xffff 33 : 0xffff 17/0xff 0
+    9.9.9.3/24 9.9.9.7/24 32 : 0xffff 33 : 0xffff 17/0xff 1
+    9.9.9.3/24 9.9.9.7/24 32 : 0xffff 33 : 0xffff 6/0xff 2
+    9.9.8.3/24 9.9.8.7/24 32 : 0xffff 33 : 0xffff 6/0xff 3
+    6.7.8.9/24 2.3.4.5/24 32 : 0x0000 33 : 0x0000 132/0xff 4
+
+Explanation
+-----------
+
+The following sections provide an explanation of the main components of the
+code.
+
+All DPDK library functions used in the sample code are prefixed with ``rte_``
+and are explained in detail in the *DPDK API Documentation*.
+
+ACL field definitions for the IPv4 5 tuple rule
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following field definitions are used when creating the ACL table during
+initialisation of the ``Flow Classify`` application..
+
+.. code-block:: c
+
+     enum {
+         PROTO_FIELD_IPV4,
+         SRC_FIELD_IPV4,
+         DST_FIELD_IPV4,
+         SRCP_FIELD_IPV4,
+         DSTP_FIELD_IPV4,
+         NUM_FIELDS_IPV4
+    };
+
+    enum {
+        PROTO_INPUT_IPV4,
+        SRC_INPUT_IPV4,
+        DST_INPUT_IPV4,
+        SRCP_DESTP_INPUT_IPV4
+    };
+
+    static struct rte_acl_field_def ipv4_defs[NUM_FIELDS_IPV4] = {
+        /* first input field - always one byte long. */
+        {
+            .type = RTE_ACL_FIELD_TYPE_BITMASK,
+            .size = sizeof(uint8_t),
+            .field_index = PROTO_FIELD_IPV4,
+            .input_index = PROTO_INPUT_IPV4,
+            .offset = sizeof(struct ether_hdr) +
+                offsetof(struct ipv4_hdr, next_proto_id),
+        },
+        /* next input field (IPv4 source address) - 4 consecutive bytes. */
+        {
+            /* rte_flow uses a bit mask for IPv4 addresses */
+            .type = RTE_ACL_FIELD_TYPE_BITMASK,
+            .size = sizeof(uint32_t),
+            .field_index = SRC_FIELD_IPV4,
+            .input_index = SRC_INPUT_IPV4,
+            .offset = sizeof(struct ether_hdr) +
+                offsetof(struct ipv4_hdr, src_addr),
+        },
+        /* next input field (IPv4 destination address) - 4 consecutive bytes. */
+        {
+            /* rte_flow uses a bit mask for IPv4 addresses */
+            .type = RTE_ACL_FIELD_TYPE_BITMASK,
+            .size = sizeof(uint32_t),
+            .field_index = DST_FIELD_IPV4,
+            .input_index = DST_INPUT_IPV4,
+            .offset = sizeof(struct ether_hdr) +
+                offsetof(struct ipv4_hdr, dst_addr),
+        },
+        /*
+         * Next 2 fields (src & dst ports) form 4 consecutive bytes.
+         * They share the same input index.
+         */
+	{
+            /* rte_flow uses a bit mask for protocol ports */
+            .type = RTE_ACL_FIELD_TYPE_BITMASK,
+            .size = sizeof(uint16_t),
+            .field_index = SRCP_FIELD_IPV4,
+            .input_index = SRCP_DESTP_INPUT_IPV4,
+            .offset = sizeof(struct ether_hdr) +
+                sizeof(struct ipv4_hdr) +
+                offsetof(struct tcp_hdr, src_port),
+        },
+        {
+             /* rte_flow uses a bit mask for protocol ports */
+             .type = RTE_ACL_FIELD_TYPE_BITMASK,
+             .size = sizeof(uint16_t),
+             .field_index = DSTP_FIELD_IPV4,
+             .input_index = SRCP_DESTP_INPUT_IPV4,
+             .offset = sizeof(struct ether_hdr) +
+                 sizeof(struct ipv4_hdr) +
+                 offsetof(struct tcp_hdr, dst_port),
+        },
+    };
+
+The Main Function
+~~~~~~~~~~~~~~~~~
+
+The ``main()`` function performs the initialization and calls the execution
+threads for each lcore.
+
+The first task is to initialize the Environment Abstraction Layer (EAL).
+The ``argc`` and ``argv`` arguments are provided to the ``rte_eal_init()``
+function. The value returned is the number of parsed arguments:
+
+.. code-block:: c
+
+    int ret = rte_eal_init(argc, argv);
+    if (ret < 0)
+        rte_exit(EXIT_FAILURE, "Error with EAL initialization\n");
+
+It then parses the flow_classify application arguments
+
+.. code-block:: c
+
+    ret = parse_args(argc, argv);
+    if (ret < 0)
+        rte_exit(EXIT_FAILURE, "Invalid flow_classify parameters\n");
+
+The ``main()`` function also allocates a mempool to hold the mbufs
+(Message Buffers) used by the application:
+
+.. code-block:: c
+
+    mbuf_pool = rte_mempool_create("MBUF_POOL",
+                                   NUM_MBUFS * nb_ports,
+                                   MBUF_SIZE,
+                                   MBUF_CACHE_SIZE,
+                                   sizeof(struct rte_pktmbuf_pool_private),
+                                   rte_pktmbuf_pool_init, NULL,
+                                   rte_pktmbuf_init, NULL,
+                                   rte_socket_id(),
+                                   0);
+
+mbufs are the packet buffer structure used by DPDK. They are explained in
+detail in the "Mbuf Library" section of the *DPDK Programmer's Guide*.
+
+The ``main()`` function also initializes all the ports using the user defined
+``port_init()`` function which is explained in the next section:
+
+.. code-block:: c
+
+    for (portid = 0; portid < nb_ports; portid++) {
+        if (port_init(portid, mbuf_pool) != 0) {
+            rte_exit(EXIT_FAILURE,
+                     "Cannot init port %" PRIu8 "\n", portid);
+        }
+    }
+
+The ``main()`` function creates the ``flow classifier object`` and adds an ``ACL
+table`` to the flow classifer.
+
+.. code-block:: c
+
+    struct flow_classifier {
+        struct rte_flow_classifier *cls;
+        uint32_t table_id[RTE_FLOW_CLASSIFY_TABLE_MAX];
+    };
+
+    struct flow_classifier_acl {
+        struct flow_classifier cls;
+    } __rte_cache_aligned;
+
+    /* Memory allocation */
+    size = RTE_CACHE_LINE_ROUNDUP(sizeof(struct flow_classifier_acl));
+    cls_app = rte_zmalloc(NULL, size, RTE_CACHE_LINE_SIZE);
+    if (cls_app == NULL)
+        rte_exit(EXIT_FAILURE, "Cannot allocate classifier memory\n");
+
+    cls_params.name = "flow_classifier";
+    cls_params.socket_id = socket_id;
+    cls_params.type = RTE_FLOW_CLASSIFY_TABLE_TYPE_ACL;
+
+    cls_app->cls = rte_flow_classifier_create(&cls_params);
+    if (cls_app->cls == NULL) {
+        rte_free(cls_app);
+        rte_exit(EXIT_FAILURE, "Cannot create classifier\n");
+    }
+
+    /* initialise ACL table params */
+    table_acl_params.name = "table_acl_ipv4_5tuple";
+    table_acl_params.n_rule_fields = RTE_DIM(ipv4_defs);
+    table_acl_params.n_rules = FLOW_CLASSIFY_MAX_RULE_NUM;
+    memcpy(table_acl_params.field_format, ipv4_defs, sizeof(ipv4_defs));
+
+    /* initialise table create params */
+    cls_table_params.ops = &rte_table_acl_ops,
+    cls_table_params.arg_create = &table_acl_params,
+    cls_table_params.table_metadata_size = 0;
+
+    ret = rte_flow_classify_table_create(cls_app->cls, &cls_table_params,
+                  &cls->table_id[0]);
+    if (ret) {
+        rte_flow_classifier_free(cls_app->cls);
+        rte_free(cls);
+        rte_exit(EXIT_FAILURE, "Failed to create classifier table\n");
+    }
+
+It then reads the ipv4_rules_file.txt file and initialises the parameters for
+the ``rte_flow_classify_table_entry_add`` API.
+This API adds a rule to the ACL table.
+
+.. code-block:: c
+
+    if (add_rules(parm_config.rule_ipv4_name)) {
+        rte_flow_classifier_free(cls_app->cls);
+        rte_free(cls_app);
+        rte_exit(EXIT_FAILURE, "Failed to add rules\n");
+    }
+
+Once the initialization is complete, the application is ready to launch a
+function on an lcore. In this example ``lcore_main()`` is called on a single
+lcore.
+
+.. code-block:: c
+
+    lcore_main(cls_app);
+
+The ``lcore_main()`` function is explained below.
+
+The Port Initialization  Function
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The main functional part of the port initialization used in the Basic
+Forwarding application is shown below:
+
+.. code-block:: c
+
+    static inline int
+    port_init(uint8_t port, struct rte_mempool *mbuf_pool)
+    {
+        struct rte_eth_conf port_conf = port_conf_default;
+        const uint16_t rx_rings = 1, tx_rings = 1;
+        struct ether_addr addr;
+        int retval;
+        uint16_t q;
+
+        if (port >= rte_eth_dev_count())
+            return -1;
+
+        /* Configure the Ethernet device. */
+        retval = rte_eth_dev_configure(port, rx_rings, tx_rings, &port_conf);
+        if (retval != 0)
+            return retval;
+
+        /* Allocate and set up 1 RX queue per Ethernet port. */
+        for (q = 0; q < rx_rings; q++) {
+            retval = rte_eth_rx_queue_setup(port, q, RX_RING_SIZE,
+                    rte_eth_dev_socket_id(port), NULL, mbuf_pool);
+            if (retval < 0)
+                return retval;
+        }
+
+        /* Allocate and set up 1 TX queue per Ethernet port. */
+        for (q = 0; q < tx_rings; q++) {
+            retval = rte_eth_tx_queue_setup(port, q, TX_RING_SIZE,
+                    rte_eth_dev_socket_id(port), NULL);
+            if (retval < 0)
+                return retval;
+        }
+
+        /* Start the Ethernet port. */
+        retval = rte_eth_dev_start(port);
+        if (retval < 0)
+            return retval;
+
+        /* Display the port MAC address. */
+        rte_eth_macaddr_get(port, &addr);
+        printf("Port %u MAC: %02" PRIx8 " %02" PRIx8 " %02" PRIx8
+               " %02" PRIx8 " %02" PRIx8 " %02" PRIx8 "\n",
+               port,
+               addr.addr_bytes[0], addr.addr_bytes[1],
+               addr.addr_bytes[2], addr.addr_bytes[3],
+               addr.addr_bytes[4], addr.addr_bytes[5]);
+
+        /* Enable RX in promiscuous mode for the Ethernet device. */
+        rte_eth_promiscuous_enable(port);
+
+        return 0;
+    }
+
+The Ethernet ports are configured with default settings using the
+``rte_eth_dev_configure()`` function and the ``port_conf_default`` struct.
+
+.. code-block:: c
+
+    static const struct rte_eth_conf port_conf_default = {
+        .rxmode = { .max_rx_pkt_len = ETHER_MAX_LEN }
+    };
+
+For this example the ports are set up with 1 RX and 1 TX queue using the
+``rte_eth_rx_queue_setup()`` and ``rte_eth_tx_queue_setup()`` functions.
+
+The Ethernet port is then started:
+
+.. code-block:: c
+
+    retval  = rte_eth_dev_start(port);
+
+
+Finally the RX port is set in promiscuous mode:
+
+.. code-block:: c
+
+    rte_eth_promiscuous_enable(port);
+
+The Add Rules function
+~~~~~~~~~~~~~~~~~~~~~~
+
+The ``add_rules`` function reads the ``ipv4_rules_file.txt`` file and calls the
+``add_classify_rule`` function which calls the
+``rte_flow_classify_table_entry_add`` API.
+
+.. code-block:: c
+
+    static int
+    add_rules(const char *rule_path)
+    {
+        FILE *fh;
+        char buff[LINE_MAX];
+        unsigned int i = 0;
+        unsigned int total_num = 0;
+        struct rte_eth_ntuple_filter ntuple_filter;
+
+        fh = fopen(rule_path, "rb");
+        if (fh == NULL)
+            rte_exit(EXIT_FAILURE, "%s: Open %s failed\n", __func__,
+                     rule_path);
+
+        fseek(fh, 0, SEEK_SET);
+
+        i = 0;
+        while (fgets(buff, LINE_MAX, fh) != NULL) {
+            i++;
+
+            if (is_bypass_line(buff))
+                continue;
+
+            if (total_num >= FLOW_CLASSIFY_MAX_RULE_NUM - 1) {
+                printf("\nINFO: classify rule capacity %d reached\n",
+                       total_num);
+                break;
+            }
+
+            if (parse_ipv4_5tuple_rule(buff, &ntuple_filter) != 0)
+                rte_exit(EXIT_FAILURE,
+                         "%s Line %u: parse rules error\n",
+                         rule_path, i);
+
+            if (add_classify_rule(&ntuple_filter) != 0)
+                rte_exit(EXIT_FAILURE, "add rule error\n");
+
+            total_num++;
+	}
+
+	fclose(fh);
+	return 0;
+    }
+
+
+The Lcore Main function
+~~~~~~~~~~~~~~~~~~~~~~~
+
+As we saw above the ``main()`` function calls an application function on the
+available lcores.
+The ``lcore_main`` function calls the ``rte_flow_classifier_query`` API.
+For the Basic Forwarding application the ``lcore_main`` function looks like the
+following:
+
+.. code-block:: c
+
+    /* flow classify data */
+    static int num_classify_rules;
+    static struct rte_flow_classify_rule *rules[MAX_NUM_CLASSIFY];
+    static struct rte_flow_classify_ipv4_5tuple_stats ntuple_stats;
+    static struct rte_flow_classify_stats classify_stats = {
+            .stats = (void *)&ntuple_stats
+    };
+
+    static __attribute__((noreturn)) void
+    lcore_main(cls_app)
+    {
+        const uint8_t nb_ports = rte_eth_dev_count();
+        uint8_t port;
+
+        /*
+         * Check that the port is on the same NUMA node as the polling thread
+         * for best performance.
+         */
+        for (port = 0; port < nb_ports; port++)
+            if (rte_eth_dev_socket_id(port) > 0 &&
+                rte_eth_dev_socket_id(port) != (int)rte_socket_id()) {
+                printf("\n\n");
+                printf("WARNING: port %u is on remote NUMA node\n",
+                       port);
+                printf("to polling thread.\n");
+                printf("Performance will not be optimal.\n");
+
+                printf("\nCore %u forwarding packets. \n",
+                       rte_lcore_id());
+                printf("[Ctrl+C to quit]\n
+            }
+
+        /* Run until the application is quit or killed. */
+        for (;;) {
+            /*
+             * Receive packets on a port and forward them on the paired
+             * port. The mapping is 0 -> 1, 1 -> 0, 2 -> 3, 3 -> 2, etc.
+             */
+            for (port = 0; port < nb_ports; port++) {
+
+                /* Get burst of RX packets, from first port of pair. */
+                struct rte_mbuf *bufs[BURST_SIZE];
+                const uint16_t nb_rx = rte_eth_rx_burst(port, 0,
+                        bufs, BURST_SIZE);
+
+                if (unlikely(nb_rx == 0))
+                    continue;
+
+                for (i = 0; i < MAX_NUM_CLASSIFY; i++) {
+                    if (rules[i]) {
+                        ret = rte_flow_classifier_query(
+                            cls_app->cls,
+                            cls_app->table_id[0],
+                            bufs, nb_rx, rules[i],
+                            &classify_stats);
+                        if (ret)
+                            printf(
+                                "rule [%d] query failed ret [%d]\n\n",
+                                i, ret);
+                        else {
+                            printf(
+                                "rule[%d] count=%"PRIu64"\n",
+                                i, ntuple_stats.counter1);
+
+                            printf("proto = %d\n",
+                                ntuple_stats.ipv4_5tuple.proto);
+                        }
+                     }
+                 }
+
+                /* Send burst of TX packets, to second port of pair. */
+                const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
+                        bufs, nb_rx);
+
+                /* Free any unsent packets. */
+                if (unlikely(nb_tx < nb_rx)) {
+                    uint16_t buf;
+                    for (buf = nb_tx; buf < nb_rx; buf++)
+                        rte_pktmbuf_free(bufs[buf]);
+                }
+            }
+        }
+    }
+
+The main work of the application is done within the loop:
+
+.. code-block:: c
+
+        for (;;) {
+            for (port = 0; port < nb_ports; port++) {
+
+                /* Get burst of RX packets, from first port of pair. */
+                struct rte_mbuf *bufs[BURST_SIZE];
+                const uint16_t nb_rx = rte_eth_rx_burst(port, 0,
+                        bufs, BURST_SIZE);
+
+                if (unlikely(nb_rx == 0))
+                    continue;
+
+                /* Send burst of TX packets, to second port of pair. */
+                const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
+                        bufs, nb_rx);
+
+                /* Free any unsent packets. */
+                if (unlikely(nb_tx < nb_rx)) {
+                    uint16_t buf;
+                    for (buf = nb_tx; buf < nb_rx; buf++)
+                        rte_pktmbuf_free(bufs[buf]);
+                }
+            }
+        }
+
+Packets are received in bursts on the RX ports and transmitted in bursts on
+the TX ports. The ports are grouped in pairs with a simple mapping scheme
+using the an XOR on the port number::
+
+    0 -> 1
+    1 -> 0
+
+    2 -> 3
+    3 -> 2
+
+    etc.
+
+The ``rte_eth_tx_burst()`` function frees the memory buffers of packets that
+are transmitted. If packets fail to transmit, ``(nb_tx < nb_rx)``, then they
+must be freed explicitly using ``rte_pktmbuf_free()``.
+
+The forwarding loop can be interrupted and the application closed using
+``Ctrl-C``.
diff --git a/doc/guides/sample_app_ug/index.rst b/doc/guides/sample_app_ug/index.rst
index 0c17ebb..6e66046 100644
--- a/doc/guides/sample_app_ug/index.rst
+++ b/doc/guides/sample_app_ug/index.rst
@@ -78,6 +78,7 @@  Sample Applications User Guides
     ptpclient
     performance_thread
     ipsec_secgw
+    flow_classify
 
 **Figures**