table of contents
IEEE80211_OUTPUT(9) | Kernel Developer's Manual | IEEE80211_OUTPUT(9) |
NAME¶
ieee80211_output — software 802.11 stack output functionsSYNOPSIS¶
#include <net80211/ieee80211_var.h> intM_WME_GETAC(struct mbuf *); int
M_SEQNO_GET(struct mbuf *); struct ieee80211_key *
ieee80211_crypto_encap(struct ieee80211_node *, struct mbuf *); void
ieee80211_process_callback(struct ieee80211_node *, struct mbuf *, int);
DESCRIPTION¶
The net80211 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 net80211 layer (e.g. management frames) or are passed down from upper layers through the ifnet(9) transmit queue. Data frames passed down for transmit flow through net80211 which handles aggregation, 802.11 encapsulation, and then dispatches the frames to the driver through it's transmit queue. There are two control paths by which frames reach a driver for transmit. Data packets are queued to the device's if_snd queue and the driver's if_start method is called. Other frames are passed down using the ic_raw_xmit method without queueing (unless done by the driver). The raw transmit path may include data frames from user applications that inject them through bpf(4) and NullData frames generated by net80211 to probe for idle stations (when operating as an access point). net80211 handles all state-related bookkeeping and management for the handling of data frames. Data frames are only transmit for a vap in theIEEE80211_S_RUN
state; there is no need, for
example, to check for frames sent down when CAC or CSA is active. Similarly,
net80211 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”.
All frames passed to a driver for transmit hold a reference to a node table
entry in the m_pkthdr.rcvif 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 ieee80211_free_node() when the transmit work
is completed. The rule to remember is: net80211 passes
responsibility for the mbuf and “node
reference” to the driver with each frame it hands off for transmit.
PACKET CLASSIFICATION¶
All frames passed by net80211 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 M_WME_GETAC() macro. PAE/EAPOL frames are tagged with anM_EAPOL
mbuf flag;
drivers should transmit them with care, usually by using the transmit rate for
management frames. Multicast/broadcast frames are marked with the
M_MCAST
mbuf flag. Frames coming out of a station's
power save queue and that have more frames immediately following are marked
with the M_MORE_DATA
mbuf flag. Such frames will be
queued consecutively in the driver's if_snd queue and
drivers should preserve the ordering when passing them to the device.
FRAGMENTED FRAMES¶
The net80211 layer will fragment data frames according to the setting of iv_fragthreshold if a driver marks theIEEE80211_C_TXFRAG
capability. Fragmented frames are
placed in the devices transmit queue with the fragments chained together with
m_nextpkt. Each frame is marked with the
M_FRAG
mbuf flag, and the first and last are marked
with M_FIRSTFRAG
and
M_LASTFRAG
, respectively. Drivers are expected to
process all fragments or none.
TRANSMIT CALLBACKS¶
Frames sent by net80211 may be tagged with theM_TXCB
mbuf flag to indicate a callback should be done
when their transmission completes. The callback is done using
ieee80211_process_callback() with the last parameter set to
a non-zero value if an error occurred and zero otherwise. Note
net80211 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.
SEE ALSO¶
bpf(4), ieee80211(9), ifnet(9)March 29, 2010 | Debian |