Manual Reference Pages - IEEE80211_OUTPUT (9)
- software 802.11 stack output functions
M_WME_GETAC struct mbuf *
M_SEQNO_GET struct mbuf *
struct ieee80211_key *
ieee80211_crypto_encap struct ieee80211_node * struct mbuf *
struct ieee80211_node *
struct mbuf *
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
prepare any hardware-specific state,
push the packet out to the device.
Outbound frames are either generated by the
layer (e.g. management frames) or are passed down
from upper layers through the
Data frames passed down for transmit flow through
which handles aggregation, 802.11 encapsulation, and then
dispatches the frames to the driver through its transmit queue.
There are two control paths by which frames reach a driver for transmit.
Data packets are queued to the devices
queue and the drivers
method is called.
Other frames are passed down using the
method without queueing (unless done by the driver).
The raw transmit path may include data frames from user applications
that inject them through
and NullData frames generated by
to probe for idle stations (when operating as an access point).
handles all state-related bookkeeping and management for the handling
of data frames.
Data frames are only transmit for a vap in the
state; there is no need, for example, to check for frames sent down
when CAC or CSA is active.
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
All frames passed to a driver for transmit hold a reference to a
node table entry in the
The node is associated with the frame destination.
Typically it is the receivers 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
when the transmit work is completed.
The rule to remember is:
passes responsibility for the
to the driver with each frame it hands off for transmit.
All frames passed by
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
The resulting AC is attached to the mbuf and may be read back using the
PAE/EAPOL frames are tagged with an
mbuf flag; drivers should transmit them with care, usually by
using the transmit rate for management frames.
Multicast/broadcast frames are marked with the
Frames coming out of a stations power save queue and that have
more frames immediately following are marked with the
Such frames will be queued consecutively in the drivers
queue and drivers should preserve the ordering when passing
them to the device.
layer will fragment data frames according to the setting of
if a driver marks the
Fragmented frames are placed
in the devices transmit queue with the fragments chained together with
.Vt m_nextpkt .
Each frame is marked with the
mbuf flag, and the first and last are marked with
Drivers are expected to process all fragments or none.
Frames sent by
may be tagged with the
mbuf flag to indicate a callback should be done
when their transmission completes.
The callback is done using
with the last parameter set to a non-zero value if an error occurred
and zero otherwise.
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.
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