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<h1 id="mqueue">Mqueue</h1>
<p>Mqueue (Mbuf event queue) is a set of API built on top of the mbuf and event queue code. A typical networking stack operation is to put a packet on a queue and post an event to the task handling that queue. Mqueue was designed to provide a common API so that individual packages would not each have to create similar code.</p>
<p>The mqueue data structure consists of a queue head pointer (a "stailq" queue; a singly linked list with head structure having a pointer to the start and end of the list) and an os event structure. Packets (packet header mbufs) are added to the queue using the <em>omp_next</em> pointer in the <code>os_mbuf_pkthdr</code> structure of the mbuf. The event is used to post to the task an event of type OS_EVENT_T_MQUEUE_DATA. </p>
<p><br> </p>
<h3 id="using-mqueue">Using Mqueue</h3>
<p>The following code sample will demonstrate how to use an mqueue. This is a simple example where packets are put on a "receive queue" and a task processes that "receive queue" by incrementing the total number of packet received and then freeing the packet. Not shown in the code example is a call my_task_rx_data_func. Presumably, some other code will call this API. </p>
<p><br></p>
<div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #A90D91">uint32_t</span> <span style="color: #000000">pkts_rxd</span>;
<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">os_mqueue</span> <span style="color: #000000">rxpkt_q</span>;
<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">os_eventq</span> <span style="color: #000000">my_task_evq</span>;
<span style="color: #A90D91">void</span>
<span style="color: #000000">process_rx_data_queue</span>(<span style="color: #A90D91">void</span>)
{
<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">os_mbuf</span> <span style="color: #000000">*om</span>;
<span style="color: #177500">/* Drain all packets off queue and process them */</span>
<span style="color: #A90D91">while</span> ((<span style="color: #000000">om</span> <span style="color: #000000">=</span> <span style="color: #000000">os_mqueue_get</span>(<span style="color: #000000">&amp;rxpkt_q</span>)) <span style="color: #000000">!=</span> <span style="color: #A90D91">NULL</span>) {
<span style="color: #000000">++pkts_rxd</span>;
<span style="color: #000000">os_mbuf_free_chain</span>(<span style="color: #000000">om</span>);
}
}
<span style="color: #A90D91">int</span>
<span style="color: #000000">my_task_rx_data_func</span>(<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">os_mbuf</span> <span style="color: #000000">*om</span>)
{
<span style="color: #A90D91">int</span> <span style="color: #000000">rc</span>;
<span style="color: #000000">rc</span> <span style="color: #000000">=</span> <span style="color: #000000">os_mqueue_put</span>(<span style="color: #000000">&amp;rxpkt_q</span>, <span style="color: #000000">&amp;my_task_evq</span>, <span style="color: #000000">om</span>);
<span style="color: #A90D91">if</span> (<span style="color: #000000">rc</span> <span style="color: #000000">!=</span> <span style="color: #1C01CE">0</span>) {
<span style="color: #A90D91">return</span> <span style="color: #1C01CE">-1</span>;
}
<span style="color: #A90D91">return</span> <span style="color: #1C01CE">0</span>;
}
<span style="color: #A90D91">void</span>
<span style="color: #000000">my_task_handler</span>(<span style="color: #A90D91">void</span> <span style="color: #000000">*arg</span>)
{
<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">os_event</span> <span style="color: #000000">*ev</span>;
<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">os_callout_func</span> <span style="color: #000000">*cf</span>;
<span style="color: #A90D91">int</span> <span style="color: #000000">rc</span>;
<span style="color: #177500">/* Initialize eventq */</span>
<span style="color: #000000">os_eventq_init</span>(<span style="color: #000000">&amp;my_task_evq</span>);
<span style="color: #177500">/* Initialize mqueue */</span>
<span style="color: #000000">os_mqueue_init</span>(<span style="color: #000000">&amp;rxpkt_q</span>, <span style="color: #A90D91">NULL</span>);
<span style="color: #A90D91">while</span> (<span style="color: #1C01CE">1</span>) {
<span style="color: #000000">ev</span> <span style="color: #000000">=</span> <span style="color: #000000">os_eventq_get</span>(<span style="color: #000000">&amp;my_task_evq</span>);
<span style="color: #A90D91">switch</span> (<span style="color: #000000">ev-&gt;ev_type</span>) {
<span style="color: #A90D91">case</span> <span style="color: #000000">OS_EVENT_T_MQUEUE_DATA</span>:
<span style="color: #000000">process_rx_data_queue</span>();
<span style="color: #A90D91">break</span>;
<span style="color: #A90D91">default</span><span style="color: #000000">:</span>
<span style="color: #000000">assert</span>(<span style="color: #1C01CE">0</span>);
<span style="color: #A90D91">break</span>;
}
}
}
</code></pre></div>
<h3 id="data-structures">Data Structures</h3>
<div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #A90D91">struct</span> <span style="color: #3F6E75">os_mqueue</span> {
<span style="color: #000000">STAILQ_HEAD</span>(, <span style="color: #000000">os_mbuf_pkthdr</span>) <span style="color: #000000">mq_head</span>;
<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">os_event</span> <span style="color: #000000">mq_ev</span>;
};
</code></pre></div>
<p><br></p>
<h3 id="list-of-functions">List of Functions</h3>
<p>The functions available in Mqueue are:</p>
<table>
<thead>
<tr>
<th><strong>Function</strong></th>
<th><strong>Description</strong></th>
</tr>
</thead>
<tbody>
<tr>
<td><a href="../os_mqueue_init/">os_mqueue_init</a></td>
<td>Initializes an mqueue.</td>
</tr>
<tr>
<td><a href="../os_mqueue_get/">os_mqueue_get</a></td>
<td>Retrieves a packet off an Mqueue.</td>
</tr>
<tr>
<td><a href="../os_mqueue_put/">os_mqueue_put</a></td>
<td>Adds a packet (i.e. packet header mbuf) to an mqueue.</td>
</tr>
</tbody>
</table>
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