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From: Gadre Nayan <gadrenayan@gmail.com>
Date: Mon, 18 Jul 2016 21:12:21 +0530
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To: users@dpdk.org
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Subject: [dpdk-users] Tracking pipeline ports.
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Hi,

I wanted to understand the purpose of the f_track function.

In the IP_pipeline example there are 2 instances where the f_track is used.

1. pipeline_firewall:
static int pipeline_firewall_track(void *pipeline, __rte_unused
uint32_t port_in,
        uint32_t *port_out)
{
        struct pipeline *p = (struct pipeline *) pipeline;

        /* Check input arguments */
        if ((p == NULL) ||
                (port_in >= p->n_ports_in) ||
                (port_out == NULL))
                return -1;

        if (p->n_ports_in == 1) {
                *port_out = 0;
                return 0;
        }

        return -1;
}

2. Passthrough:

static int
pipeline_passthrough_track(void *pipeline, uint32_t port_in, uint32_t *port_out)
{
        struct pipeline *p = (struct pipeline *) pipeline;

        /* Check input arguments */
        if ((p == NULL) ||
                (port_in >= p->n_ports_in) ||
                (port_out == NULL))
                return -1;

        *port_out = port_in / p->n_ports_in;
        return 0;
}

1. What is a actual use of this function ?
Quoting the documentation:
"In some cases, it is useful for a pipeline instance to get
application level information related to pipeline connectivity, such
as to identify the output link (e.g. physical NIC port) where one of
its output ports connected, either directly or indirectly by
traversing other pipeline instances."

2. The 1st condition check remains same in both. But in pass-through
port_out is assigned some value. what does this mean ?