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download PDF document: ieee80211_sort_channels.9.pdf

IEEE80211_REGDOMAIN(9) FreeBSD Kernel Developer's Manual
NAME ieee80211_regdomain - 802.11 regulatory support
SYNOPSIS #include <net80211/ieee80211_var.h> #include <net80211/ieee80211_regdomain.h>
int ieee80211_init_channels(struct ieee80211com *, const struct ieee80211_regdomain *, const uint8_t bands[]);
void ieee80211_sort_channels(struct ieee80211_channel *, int nchans);
struct ieee80211_appie * ieee80211_alloc_countryie(struct ieee80211com *);
DESCRIPTION The net80211 software layer provides a support framework for drivers that includes comprehensive regulatory support. net80211 provides mechanisms that enforce regulatory policy by privileged user applications.
Drivers define a device's capabilities and can intercept and control regulatory changes requested through net80211. The initial regulatory state, including the channel list, must be filled in by the driver before calling ieee80211_ifattach(). The channel list should reflect the set of channels the device is calibrated for use on. This list may also be requested later through the ic_getradiocaps method in the ieee80211com structure. The ieee80211_init_channels() function is provided as a rudimentary fallback for drivers that do not (or cannot) fill in a proper channel list. Default regulatory state is supplied such as the regulatory SKU, ISO country code, location (e.g. indoor, outdoor), and a set of frequency bands the device is capable of operating on. net80211 populates the channel table in ic_channels with a default set of channels and capabilities. Note this mechanism should be used with care as any mismatch between the channel list created and the device's capabilities can result in runtime errors (e.g. a request to operate on a channel the device does not support). The SKU and country information are used for generating 802.11h protocol elements and related operation such as for 802.11d; mis-setup by a driver is not fatal, only potentially confusing.
Devices that do not have a fixed/default regulatory state can set the regulatory SKU to SKU_DEBUG and country code to CTRY_DEFAULT and leave proper setup to user applications. If default settings are known they can be installed and/or an event can be dispatched to user space using ieee80211_notify_country() so that devd(8) will do the appropriate setup work at system boot (or device insertion).
The channel table is sorted to optimize lookups using the ieee80211_sort_channels() routine. This should be done whenever the channel table contents are modified.
The ieee80211_alloc_countryie() function allocates an information element as specified by 802.11h. Because this is expensive to generate it is cached in ic_countryie and generated only when regulatory state changes. Drivers that call ieee80211_alloc_countryie() directly should not help with this caching; doing so may confuse the net80211 layer. transmit power cap for a channel is too high the driver can either reject the request or (better) reduce the cap to be compliant. Requests that include unacceptable channels should cause the request to be rejected as otherwise a mismatch may be created between application state and the state managed by net80211. The exact rules by which to operate are still being codified.
SEE ALSO regdomain(5), ifconfig(8), ieee80211(9)
FreeBSD 14.0-RELEASE-p11 August 4, 2009 FreeBSD 14.0-RELEASE-p11