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<table class="head">
<tr>
<td class="head-ltitle">IEEE80211_OUTPUT(9)</td>
<td class="head-vol">Kernel Developer's Manual</td>
<td class="head-rtitle">IEEE80211_OUTPUT(9)</td>
</tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp"><code class="Nm">ieee80211_output</code> —
<span class="Nd">software 802.11 stack output functions</span></p>
</section>
<section class="Sh">
<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1>
<p class="Pp"><code class="In">#include
<<a class="In">net80211/ieee80211_var.h</a>></code></p>
<p class="Pp"><var class="Ft">int</var>
<br/>
<code class="Fn">M_WME_GETAC</code>(<var class="Fa" style="white-space: nowrap;">struct
mbuf *</var>);</p>
<p class="Pp"><var class="Ft">int</var>
<br/>
<code class="Fn">M_SEQNO_GET</code>(<var class="Fa" style="white-space: nowrap;">struct
mbuf *</var>);</p>
<p class="Pp"><var class="Ft">struct ieee80211_key *</var>
<br/>
<code class="Fn">ieee80211_crypto_encap</code>(<var class="Fa" style="white-space: nowrap;">struct
ieee80211_node *</var>, <var class="Fa" style="white-space: nowrap;">struct
mbuf *</var>);</p>
<p class="Pp"><var class="Ft">void</var>
<br/>
<code class="Fn">ieee80211_process_callback</code>(<var class="Fa">struct
ieee80211_node *</var>, <var class="Fa">struct mbuf *</var>,
<var class="Fa">int</var>);</p>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp">The <code class="Nm">net80211</code> layer that supports 802.11
device drivers handles most of the work required to transmit frames. Drivers
usually receive fully-encapsulated 802.11 frames that have been classified
and assigned a transmit priority; all that is left is to do crypto
encapsulation, prepare any hardware-specific state, and push the packet out
to the device. Outbound frames are either generated by the
<code class="Nm">net80211</code> layer (e.g. management frames) or are
passed down from upper layers through the <a class="Xr">ifnet(9)</a>
transmit queue. Data frames passed down for transmit flow through
<code class="Nm">net80211</code> which handles aggregation, 802.11
encapsulation, and then dispatches the frames to the driver through it's
transmit queue.</p>
<p class="Pp">There are two control paths by which frames reach a driver for
transmit. Data packets are queued to the device's
<var class="Vt">if_snd</var> queue and the driver's
<var class="Vt">if_start</var> method is called. Other frames are passed
down using the <var class="Vt">ic_raw_xmit</var> method without queueing
(unless done by the driver). The raw transmit path may include data frames
from user applications that inject them through <a class="Xr">bpf(4)</a> and
NullData frames generated by <code class="Nm">net80211</code> to probe for
idle stations (when operating as an access point).</p>
<p class="Pp"><code class="Nm">net80211</code> handles all state-related
bookkeeping and management for the handling of data frames. Data frames are
only transmit for a vap in the <code class="Dv">IEEE80211_S_RUN</code>
state; there is no need, for example, to check for frames sent down when CAC
or CSA is active. Similarly, <code class="Nm">net80211</code> handles
activities such as background scanning and power save mode, frames will not
be sent to a driver unless it is operating on the BSS channel with
“full power”.</p>
<p class="Pp" id="ieee80211_free_node">All frames passed to a driver for
transmit hold a reference to a node table entry in the
<var class="Vt">m_pkthdr.rcvif</var> field. The node is associated with the
frame destination. Typically it is the receiver's entry but in some
situations it may be a placeholder entry or the “next hop
station” (such as in a mesh network). In all cases the reference must
be reclaimed with
<a class="permalink" href="#ieee80211_free_node"><code class="Fn">ieee80211_free_node</code></a>()
when the transmit work is completed. The rule to remember is:
<code class="Nm">net80211</code> passes responsibility for the
<var class="Vt">mbuf</var> and “node reference” to the driver
with each frame it hands off for transmit.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="PACKET_CLASSIFICATION"><a class="permalink" href="#PACKET_CLASSIFICATION">PACKET
CLASSIFICATION</a></h1>
<p class="Pp">All frames passed by <code class="Nm">net80211</code> for transmit
are assigned a priority based on any vlan tag assigned to the receiving
station and/or any Diffserv setting in an IP or IPv6 header. If both vlan
and Diffserv priority are present the higher of the two is used. If WME/WMM
is being used then any ACM policy (in station mode) is also enforced. The
resulting AC is attached to the mbuf and may be read back using the
<a class="permalink" href="#M_WME_GETAC"><code class="Fn" id="M_WME_GETAC">M_WME_GETAC</code></a>()
macro.</p>
<p class="Pp">PAE/EAPOL frames are tagged with an
<code class="Dv">M_EAPOL</code> mbuf flag; drivers should transmit them with
care, usually by using the transmit rate for management frames.
Multicast/broadcast frames are marked with the
<code class="Dv">M_MCAST</code> mbuf flag. Frames coming out of a station's
power save queue and that have more frames immediately following are marked
with the <code class="Dv">M_MORE_DATA</code> mbuf flag. Such frames will be
queued consecutively in the driver's <var class="Vt">if_snd</var> queue and
drivers should preserve the ordering when passing them to the device.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="FRAGMENTED_FRAMES"><a class="permalink" href="#FRAGMENTED_FRAMES">FRAGMENTED
FRAMES</a></h1>
<p class="Pp">The <code class="Nm">net80211</code> layer will fragment data
frames according to the setting of <var class="Vt">iv_fragthreshold</var> if
a driver marks the <code class="Dv">IEEE80211_C_TXFRAG</code> capability.
Fragmented frames are placed in the devices transmit queue with the
fragments chained together with <var class="Vt">m_nextpkt</var>. Each frame
is marked with the <code class="Dv">M_FRAG</code> mbuf flag, and the first
and last are marked with <code class="Dv">M_FIRSTFRAG</code> and
<code class="Dv">M_LASTFRAG</code>, respectively. Drivers are expected to
process all fragments or none.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="TRANSMIT_CALLBACKS"><a class="permalink" href="#TRANSMIT_CALLBACKS">TRANSMIT
CALLBACKS</a></h1>
<p class="Pp">Frames sent by <code class="Nm">net80211</code> may be tagged with
the <code class="Dv">M_TXCB</code> mbuf flag to indicate a callback should
be done when their transmission completes. The callback is done using
<a class="permalink" href="#ieee80211_process_callback"><code class="Fn" id="ieee80211_process_callback">ieee80211_process_callback</code></a>()
with the last parameter set to a non-zero value if an error occurred and
zero otherwise. Note <code class="Nm">net80211</code> understands that
drivers may be incapable of determining status; a device may not report if
an ACK frame is received and/or a device may queue transmit requests in its
hardware and only report status on whether the frame was successfully
queued.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
ALSO</a></h1>
<p class="Pp"><a class="Xr">bpf(4)</a>, <a class="Xr">ieee80211(9)</a>,
<a class="Xr">ifnet(9)</a></p>
</section>
</div>
<table class="foot">
<tr>
<td class="foot-date">March 29, 2010</td>
<td class="foot-os">FreeBSD 15.0</td>
</tr>
</table>
|
