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hostapd: Add Automatic Channel Selection (ACS) support

Browse source 
This adds ACS support to hostapd. Currently only survey-based
algorithm is available.

To use ACS you need to enable CONFIG_ACS=y in .config and use
channel=0 (or channel=acs_survey) in hostapd.conf.

For more details see wiki page [1] or comments in src/ap/acs.c.

[1]: http://wireless.kernel.org/en/users/Documentation/acs

Signed-hostap: Michal Kazior <michal.kazior@tieto.com>
This commit is contained in:
Michal Kazior 2013-08-31 11:49:51 +03:00 committed by Jouni Malinen
parent 43ee470494
commit 50f4f2a066
12 changed files with 937 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

6
hostapd/Makefile
View file

@ -817,6 +817,12 @@ else
OBJS_c += ../src/utils/edit_simple.o
endif
ifdef CONFIG_ACS
CFLAGS += -DCONFIG_ACS
OBJS += ../src/ap/acs.o
LIBS += -lm
endif
ifdef CONFIG_NO_STDOUT_DEBUG
CFLAGS += -DCONFIG_NO_STDOUT_DEBUG
endif

20
hostapd/config_file.c
View file

@ -2311,7 +2311,15 @@ static int hostapd_config_fill(struct hostapd_config *conf,
errors++;
}
} else if (os_strcmp(buf, "channel") == 0) {
conf->channel = atoi(pos);
if (os_strcmp(pos, "acs_survey") == 0) {
#ifndef CONFIG_ACS
wpa_printf(MSG_ERROR, "Line %d: tries to enable ACS but CONFIG_ACS disabled",
line);
errors++;
#endif /* CONFIG_ACS */
conf->channel = 0;
} else
conf->channel = atoi(pos);
} else if (os_strcmp(buf, "beacon_int") == 0) {
int val = atoi(pos);
/* MIB defines range as 1..65535, but very small values
@ -2326,6 +2334,16 @@ static int hostapd_config_fill(struct hostapd_config *conf,
errors++;
} else
conf->beacon_int = val;
#ifdef CONFIG_ACS
} else if (os_strcmp(buf, "acs_num_scans") == 0) {
int val = atoi(pos);
if (val <= 0 || val > 100) {
wpa_printf(MSG_ERROR, "Line %d: invalid acs_num_scans %d (expected 1..100)",
line, val);
errors++;
} else
conf->acs_num_scans = val;
#endif /* CONFIG_ACS */
} else if (os_strcmp(buf, "dtim_period") == 0) {
bss->dtim_period = atoi(pos);
if (bss->dtim_period < 1 || bss->dtim_period > 255) {

24
hostapd/defconfig
View file

@ -278,3 +278,27 @@ CONFIG_IPV6=y
# certain percentage of probe requests or auth/(re)assoc frames.
#
#CONFIG_TESTING_OPTIONS=y
# Automatic Channel Selection
# This will allow hostapd to pick the channel automatically when channel is set
# to "acs_survey" or "0". Eventually, other ACS algorithms can be added in
# similar way.
#
# Automatic selection is currently only done through initialization, later on
# we hope to do background checks to keep us moving to more ideal channels as
# time goes by. ACS is currently only supported through the nl80211 driver and
# your driver must have survey dump capability that is filled by the driver
# during scanning.
#
# You can customize the ACS survey algorithm with the hostapd.conf variable
# acs_num_scans.
#
# Supported ACS drivers:
# * ath9k
# * ath5k
# * ath10k
#
# For more details refer to:
# http://wireless.kernel.org/en/users/Documentation/acs
#
#CONFIG_ACS=y

20
hostapd/hostapd.conf
View file

@ -121,8 +121,28 @@ hw_mode=g
# (default: 0, i.e., not set)
# Please note that some drivers do not use this value from hostapd and the
# channel will need to be configured separately with iwconfig.
#
# If CONFIG_ACS build option is enabled, the channel can be selected
# automatically at run time by setting channel=acs_survey or channel=0, both of
# which will enable the ACS survey based algorithm.
channel=1
# ACS tuning - Automatic Channel Selection
# See: http://wireless.kernel.org/en/users/Documentation/acs
#
# You can customize the ACS survey algorithm with following variables:
#
# acs_num_scans requirement is 1..100 - number of scans to be performed that
# are used to trigger survey data gathering of an underlying device driver.
# Scans are passive and typically take a little over 100ms (depending on the
# driver) on each available channel for given hw_mode. Increasing this value
# means sacrificing startup time and gathering more data wrt channel
# interference that may help choosing a better channel. This can also help fine
# tune the ACS scan time in case a driver has different scan dwell times.
#
# Defaults:
#acs_num_scans=5
# Beacon interval in kus (1.024 ms) (default: 100; range 15..65535)
beacon_int=100

770
src/ap/acs.c Normal file
View file

@ -0,0 +1,770 @@
/*
* ACS - Automatic Channel Selection module
* Copyright (c) 2011, Atheros Communications
* Copyright (c) 2013, Qualcomm Atheros, Inc.
*
* This software may be distributed under the terms of the BSD license.
* See README for more details.
*/
#include "utils/includes.h"
#include <math.h>
#include "utils/common.h"
#include "utils/list.h"
#include "common/ieee802_11_defs.h"
#include "drivers/driver.h"
#include "hostapd.h"
#include "ap_drv_ops.h"
#include "ap_config.h"
#include "hw_features.h"
#include "acs.h"
/*
* Automatic Channel Selection
* ===========================
*
* More info at
* ------------
* http://wireless.kernel.org/en/users/Documentation/acs
*
* How to use
* ----------
* - make sure you have CONFIG_ACS=y in hostapd's .config
* - use channel=0 or channel=acs to enable ACS
*
* How does it work
* ----------------
* 1. passive scans are used to collect survey data
* (it is assumed that scan trigger collection of survey data in driver)
* 2. interference factor is calculated for each channel
* 3. ideal channel is picked depending on channel width by using adjacent
* channel interference factors
*
* Known limitations
* -----------------
* - Current implementation depends heavily on the amount of time willing to
* spend gathering survey data during hostapd startup. Short traffic bursts
* may be missed and a suboptimal channel may be picked.
* - Ideal channel may end up overlapping a channel with 40 MHz intolerant BSS
*
* Todo / Ideas
* ------------
* - implement other interference computation methods
* - BSS/RSSI based
* - spectral scan based
* (should be possibly to hook this up with current ACS scans)
* - add wpa_supplicant support (for P2P)
* - collect a histogram of interference over time allowing more educated
* guess about an ideal channel (perhaps CSA could be used to migrate AP to a
* new "better" channel while running)
* - include neighboring BSS scan to avoid conflicts with 40 MHz intolerant BSSs
* when choosing the ideal channel
*
* Survey interference factor implementation details
* -------------------------------------------------
* Generic interference_factor in struct hostapd_channel_data is used.
*
* The survey interference factor is defined as the ratio of the
* observed busy time over the time we spent on the channel,
* this value is then amplified by the observed noise floor on
* the channel in comparison to the lowest noise floor observed
* on the entire band.
*
* This corresponds to:
* ---
* (busy time - tx time) / (active time - tx time) * 2^(chan_nf + band_min_nf)
* ---
*
* The coefficient of 2 reflects the way power in "far-field"
* radiation decreases as the square of distance from the antenna [1].
* What this does is it decreases the observed busy time ratio if the
* noise observed was low but increases it if the noise was high,
* proportionally to the way "far field" radiation changes over
* distance.
*
* If channel busy time is not available the fallback is to use channel RX time.
*
* Since noise floor is in dBm it is necessary to convert it into Watts so that
* combined channel interference (e.g., HT40, which uses two channels) can be
* calculated easily.
* ---
* (busy time - tx time) / (active time - tx time) *
* 2^(10^(chan_nf/10) + 10^(band_min_nf/10))
* ---
*
* However to account for cases where busy/rx time is 0 (channel load is then
* 0%) channel noise floor signal power is combined into the equation so a
* channel with lower noise floor is preferred. The equation becomes:
* ---
* 10^(chan_nf/5) + (busy time - tx time) / (active time - tx time) *
* 2^(10^(chan_nf/10) + 10^(band_min_nf/10))
* ---
*
* All this "interference factor" is purely subjective and only time
* will tell how usable this is. By using the minimum noise floor we
* remove any possible issues due to card calibration. The computation
* of the interference factor then is dependent on what the card itself
* picks up as the minimum noise, not an actual real possible card
* noise value.
*
* Total interference computation details
* --------------------------------------
* The above channel interference factor is calculated with no respect to
* target operational bandwidth.
*
* To find an ideal channel the above data is combined by taking into account
* the target operational bandwidth and selected band. E.g., on 2.4 GHz channels
* overlap with 20 MHz bandwidth, but there is no overlap for 20 MHz bandwidth
* on 5 GHz.
*
* Each valid and possible channel spec (i.e., channel + width) is taken and its
* interference factor is computed by summing up interferences of each channel
* it overlaps. The one with least total interference is picked up.
*
* Note: This implies base channel interference factor must be non-negative
* allowing easy summing up.
*
* Example ACS analysis printout
* -----------------------------
*
* ACS: Trying survey-based ACS
* ACS: Survey analysis for channel 1 (2412 MHz)
* ACS: 1: min_nf=-113 interference_factor=0.0802469 nf=-113 time=162 busy=0 rx=13
* ACS: 2: min_nf=-113 interference_factor=0.0745342 nf=-113 time=161 busy=0 rx=12
* ACS: 3: min_nf=-113 interference_factor=0.0679012 nf=-113 time=162 busy=0 rx=11
* ACS: 4: min_nf=-113 interference_factor=0.0310559 nf=-113 time=161 busy=0 rx=5
* ACS: 5: min_nf=-113 interference_factor=0.0248447 nf=-113 time=161 busy=0 rx=4
* ACS: * interference factor average: 0.0557166
* ACS: Survey analysis for channel 2 (2417 MHz)
* ACS: 1: min_nf=-113 interference_factor=0.0185185 nf=-113 time=162 busy=0 rx=3
* ACS: 2: min_nf=-113 interference_factor=0.0246914 nf=-113 time=162 busy=0 rx=4
* ACS: 3: min_nf=-113 interference_factor=0.037037 nf=-113 time=162 busy=0 rx=6
* ACS: 4: min_nf=-113 interference_factor=0.149068 nf=-113 time=161 busy=0 rx=24
* ACS: 5: min_nf=-113 interference_factor=0.0248447 nf=-113 time=161 busy=0 rx=4
* ACS: * interference factor average: 0.050832
* ACS: Survey analysis for channel 3 (2422 MHz)
* ACS: 1: min_nf=-113 interference_factor=2.51189e-23 nf=-113 time=162 busy=0 rx=0
* ACS: 2: min_nf=-113 interference_factor=0.0185185 nf=-113 time=162 busy=0 rx=3
* ACS: 3: min_nf=-113 interference_factor=0.0186335 nf=-113 time=161 busy=0 rx=3
* ACS: 4: min_nf=-113 interference_factor=0.0186335 nf=-113 time=161 busy=0 rx=3
* ACS: 5: min_nf=-113 interference_factor=0.0186335 nf=-113 time=161 busy=0 rx=3
* ACS: * interference factor average: 0.0148838
* ACS: Survey analysis for channel 4 (2427 MHz)
* ACS: 1: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=162 busy=0 rx=0
* ACS: 2: min_nf=-114 interference_factor=0.0555556 nf=-114 time=162 busy=0 rx=9
* ACS: 3: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=161 busy=0 rx=0
* ACS: 4: min_nf=-114 interference_factor=0.0186335 nf=-114 time=161 busy=0 rx=3
* ACS: 5: min_nf=-114 interference_factor=0.00621118 nf=-114 time=161 busy=0 rx=1
* ACS: * interference factor average: 0.0160801
* ACS: Survey analysis for channel 5 (2432 MHz)
* ACS: 1: min_nf=-114 interference_factor=0.409938 nf=-113 time=161 busy=0 rx=66
* ACS: 2: min_nf=-114 interference_factor=0.0432099 nf=-113 time=162 busy=0 rx=7
* ACS: 3: min_nf=-114 interference_factor=0.0124224 nf=-113 time=161 busy=0 rx=2
* ACS: 4: min_nf=-114 interference_factor=0.677019 nf=-113 time=161 busy=0 rx=109
* ACS: 5: min_nf=-114 interference_factor=0.0186335 nf=-114 time=161 busy=0 rx=3
* ACS: * interference factor average: 0.232244
* ACS: Survey analysis for channel 6 (2437 MHz)
* ACS: 1: min_nf=-113 interference_factor=0.552795 nf=-113 time=161 busy=0 rx=89
* ACS: 2: min_nf=-113 interference_factor=0.0807453 nf=-112 time=161 busy=0 rx=13
* ACS: 3: min_nf=-113 interference_factor=0.0310559 nf=-113 time=161 busy=0 rx=5
* ACS: 4: min_nf=-113 interference_factor=0.434783 nf=-112 time=161 busy=0 rx=70
* ACS: 5: min_nf=-113 interference_factor=0.0621118 nf=-113 time=161 busy=0 rx=10
* ACS: * interference factor average: 0.232298
* ACS: Survey analysis for channel 7 (2442 MHz)
* ACS: 1: min_nf=-113 interference_factor=0.440994 nf=-112 time=161 busy=0 rx=71
* ACS: 2: min_nf=-113 interference_factor=0.385093 nf=-113 time=161 busy=0 rx=62
* ACS: 3: min_nf=-113 interference_factor=0.0372671 nf=-113 time=161 busy=0 rx=6
* ACS: 4: min_nf=-113 interference_factor=0.0372671 nf=-113 time=161 busy=0 rx=6
* ACS: 5: min_nf=-113 interference_factor=0.0745342 nf=-113 time=161 busy=0 rx=12
* ACS: * interference factor average: 0.195031
* ACS: Survey analysis for channel 8 (2447 MHz)
* ACS: 1: min_nf=-114 interference_factor=0.0496894 nf=-112 time=161 busy=0 rx=8
* ACS: 2: min_nf=-114 interference_factor=0.0496894 nf=-114 time=161 busy=0 rx=8
* ACS: 3: min_nf=-114 interference_factor=0.0372671 nf=-113 time=161 busy=0 rx=6
* ACS: 4: min_nf=-114 interference_factor=0.12963 nf=-113 time=162 busy=0 rx=21
* ACS: 5: min_nf=-114 interference_factor=0.166667 nf=-114 time=162 busy=0 rx=27
* ACS: * interference factor average: 0.0865885
* ACS: Survey analysis for channel 9 (2452 MHz)
* ACS: 1: min_nf=-114 interference_factor=0.0124224 nf=-114 time=161 busy=0 rx=2
* ACS: 2: min_nf=-114 interference_factor=0.0310559 nf=-114 time=161 busy=0 rx=5
* ACS: 3: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=161 busy=0 rx=0
* ACS: 4: min_nf=-114 interference_factor=0.00617284 nf=-114 time=162 busy=0 rx=1
* ACS: 5: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=162 busy=0 rx=0
* ACS: * interference factor average: 0.00993022
* ACS: Survey analysis for channel 10 (2457 MHz)
* ACS: 1: min_nf=-114 interference_factor=0.00621118 nf=-114 time=161 busy=0 rx=1
* ACS: 2: min_nf=-114 interference_factor=0.00621118 nf=-114 time=161 busy=0 rx=1
* ACS: 3: min_nf=-114 interference_factor=0.00621118 nf=-114 time=161 busy=0 rx=1
* ACS: 4: min_nf=-114 interference_factor=0.0493827 nf=-114 time=162 busy=0 rx=8
* ACS: 5: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=162 busy=0 rx=0
* ACS: * interference factor average: 0.0136033
* ACS: Survey analysis for channel 11 (2462 MHz)
* ACS: 1: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=161 busy=0 rx=0
* ACS: 2: min_nf=-114 interference_factor=2.51189e-23 nf=-113 time=161 busy=0 rx=0
* ACS: 3: min_nf=-114 interference_factor=2.51189e-23 nf=-113 time=161 busy=0 rx=0
* ACS: 4: min_nf=-114 interference_factor=0.0432099 nf=-114 time=162 busy=0 rx=7
* ACS: 5: min_nf=-114 interference_factor=0.0925926 nf=-114 time=162 busy=0 rx=15
* ACS: * interference factor average: 0.0271605
* ACS: Survey analysis for channel 12 (2467 MHz)
* ACS: 1: min_nf=-114 interference_factor=0.0621118 nf=-113 time=161 busy=0 rx=10
* ACS: 2: min_nf=-114 interference_factor=0.00621118 nf=-114 time=161 busy=0 rx=1
* ACS: 3: min_nf=-114 interference_factor=2.51189e-23 nf=-113 time=162 busy=0 rx=0
* ACS: 4: min_nf=-114 interference_factor=2.51189e-23 nf=-113 time=162 busy=0 rx=0
* ACS: 5: min_nf=-114 interference_factor=0.00617284 nf=-113 time=162 busy=0 rx=1
* ACS: * interference factor average: 0.0148992
* ACS: Survey analysis for channel 13 (2472 MHz)
* ACS: 1: min_nf=-114 interference_factor=0.0745342 nf=-114 time=161 busy=0 rx=12
* ACS: 2: min_nf=-114 interference_factor=0.0555556 nf=-114 time=162 busy=0 rx=9
* ACS: 3: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=162 busy=0 rx=0
* ACS: 4: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=162 busy=0 rx=0
* ACS: 5: min_nf=-114 interference_factor=1.58489e-23 nf=-114 time=162 busy=0 rx=0
* ACS: * interference factor average: 0.0260179
* ACS: Survey analysis for selected bandwidth 20MHz
* ACS: * channel 1: total interference = 0.121432
* ACS: * channel 2: total interference = 0.137512
* ACS: * channel 3: total interference = 0.369757
* ACS: * channel 4: total interference = 0.546338
* ACS: * channel 5: total interference = 0.690538
* ACS: * channel 6: total interference = 0.762242
* ACS: * channel 7: total interference = 0.756092
* ACS: * channel 8: total interference = 0.537451
* ACS: * channel 9: total interference = 0.332313
* ACS: * channel 10: total interference = 0.152182
* ACS: * channel 11: total interference = 0.0916111
* ACS: * channel 12: total interference = 0.0816809
* ACS: * channel 13: total interference = 0.0680776
* ACS: Ideal channel is 13 (2472 MHz) with total interference factor of 0.0680776
*
* [1] http://en.wikipedia.org/wiki/Near_and_far_field
*/
static int acs_request_scan(struct hostapd_iface *iface);
static void acs_clean_chan_surveys(struct hostapd_channel_data *chan)
{
struct freq_survey *survey, *tmp;
if (dl_list_empty(&chan->survey_list))
return;
dl_list_for_each_safe(survey, tmp, &chan->survey_list,
struct freq_survey, list) {
dl_list_del(&survey->list);
os_free(survey);
}
}
static void acs_cleanup(struct hostapd_iface *iface)
{
int i;
struct hostapd_channel_data *chan;
for (i = 0; i < iface->current_mode->num_channels; i++) {
chan = &iface->current_mode->channels[i];
if (chan->flag & HOSTAPD_CHAN_SURVEY_LIST_INITIALIZED)
acs_clean_chan_surveys(chan);
dl_list_init(&chan->survey_list);
chan->flag |= HOSTAPD_CHAN_SURVEY_LIST_INITIALIZED;
chan->min_nf = 0;
}
iface->chans_surveyed = 0;
iface->acs_num_completed_scans = 0;
}
void acs_fail(struct hostapd_iface *iface)
{
wpa_printf(MSG_ERROR, "ACS: Failed to start");
acs_cleanup(iface);
}
static long double
acs_survey_interference_factor(struct freq_survey *survey, s8 min_nf)
{
long double factor, busy, total;
if (survey->filled & SURVEY_HAS_CHAN_TIME_BUSY)
busy = survey->channel_time_busy;
else if (survey->filled & SURVEY_HAS_CHAN_TIME_RX)
busy = survey->channel_time_rx;
else {
/* This shouldn't really happen as survey data is checked in
* acs_sanity_check() */
wpa_printf(MSG_ERROR, "ACS: Survey data missing");
return 0;
}
total = survey->channel_time;
if (survey->filled & SURVEY_HAS_CHAN_TIME_TX) {
busy -= survey->channel_time_tx;
total -= survey->channel_time_tx;
}
/* TODO: figure out the best multiplier for noise floor base */
factor = pow(10, survey->nf / 5.0L) +
(busy / total) *
pow(2, pow(10, (long double) survey->nf / 10.0L) -
pow(10, (long double) min_nf / 10.0L));
return factor;
}
static void
acs_survey_chan_interference_factor(struct hostapd_iface *iface,
struct hostapd_channel_data *chan)
{
struct freq_survey *survey;
unsigned int i = 0;
long double int_factor = 0;
if (dl_list_empty(&chan->survey_list))
return;
if (chan->flag & HOSTAPD_CHAN_DISABLED)
return;
chan->interference_factor = 0;
dl_list_for_each(survey, &chan->survey_list, struct freq_survey, list)
{
int_factor = acs_survey_interference_factor(survey,
iface->lowest_nf);
chan->interference_factor += int_factor;
wpa_printf(MSG_DEBUG, "ACS: %d: min_nf=%d interference_factor=%Lg nf=%d time=%lu busy=%lu rx=%lu",
++i, chan->min_nf, int_factor,
survey->nf, (unsigned long) survey->channel_time,
(unsigned long) survey->channel_time_busy,
(unsigned long) survey->channel_time_rx);
}
chan->interference_factor = chan->interference_factor /
dl_list_len(&chan->survey_list);
}
static int acs_usable_chan(struct hostapd_channel_data *chan)
{
if (dl_list_empty(&chan->survey_list))
return 0;
if (chan->flag & HOSTAPD_CHAN_DISABLED)
return 0;
return 1;
}
static int acs_usable_ht40_chan(struct hostapd_channel_data *chan)
{
const int allowed[] = { 36, 44, 52, 60, 100, 108, 116, 124, 132, 149,
157, 184, 192 };
unsigned int i;
for (i = 0; i < sizeof(allowed) / sizeof(allowed[0]); i++)
if (chan->chan == allowed[i])
return 1;
return 0;
}
static int acs_survey_is_sufficient(struct freq_survey *survey)
{
if (!(survey->filled & SURVEY_HAS_NF)) {
wpa_printf(MSG_ERROR, "ACS: Survey is missing noise floor");
return 0;
}
if (!(survey->filled & SURVEY_HAS_CHAN_TIME)) {
wpa_printf(MSG_ERROR, "ACS: Survey is missing channel time");
return 0;
}
if (!(survey->filled & SURVEY_HAS_CHAN_TIME_BUSY) &&
!(survey->filled & SURVEY_HAS_CHAN_TIME_RX)) {
wpa_printf(MSG_ERROR, "ACS: Survey is missing RX and busy time (at least one is required)");
return 0;
}
return 1;
}
static int acs_surveys_are_sufficient(struct hostapd_iface *iface)
{
int i;
struct hostapd_channel_data *chan;
struct freq_survey *survey;
for (i = 0; i < iface->current_mode->num_channels; i++) {
chan = &iface->current_mode->channels[i];
if (chan->flag & HOSTAPD_CHAN_DISABLED)
continue;
dl_list_for_each(survey, &chan->survey_list,
struct freq_survey, list)
{
if (!acs_survey_is_sufficient(survey)) {
wpa_printf(MSG_ERROR, "ACS: Channel %d has insufficient survey data",
chan->chan);
return 0;
}
}
}
return 1;
}
static void acs_survey_all_chans_intereference_factor(
struct hostapd_iface *iface)
{
int i;
struct hostapd_channel_data *chan;
for (i = 0; i < iface->current_mode->num_channels; i++) {
chan = &iface->current_mode->channels[i];
if (!acs_usable_chan(chan))
continue;
wpa_printf(MSG_DEBUG, "ACS: Survey analysis for channel %d (%d MHz)",
chan->chan, chan->freq);
acs_survey_chan_interference_factor(iface, chan);
wpa_printf(MSG_DEBUG, "ACS: * interference factor average: %Lg",
chan->interference_factor);
}
}
static struct hostapd_channel_data *acs_find_chan(struct hostapd_iface *iface,
int freq)
{
struct hostapd_channel_data *chan;
int i;
for (i = 0; i < iface->current_mode->num_channels; i++) {
chan = &iface->current_mode->channels[i];
if (!acs_usable_chan(chan))
continue;
if (chan->freq == freq)
return chan;
}
return NULL;
}
/*
* At this point it's assumed chan->interface_factor has been computed.
* This function should be reusable regardless of interference computation
* option (survey, BSS, spectral, ...). chan->interference factor must be
* summable (i.e., must be always greater than zero).
*/
static struct hostapd_channel_data *
acs_find_ideal_chan(struct hostapd_iface *iface)
{
struct hostapd_channel_data *chan, *adj_chan, *ideal_chan = NULL;
long double factor, ideal_factor = 0;
int i, j;
int n_chans = 1;
/* TODO: HT40- support */
if (iface->conf->ieee80211n &&
iface->conf->secondary_channel == -1) {
wpa_printf(MSG_ERROR, "ACS: HT40- is not supported yet. Please try HT40+");
return NULL;
}
if (iface->conf->ieee80211n &&
iface->conf->secondary_channel)
n_chans = 2;
if (iface->conf->ieee80211ac &&
iface->conf->vht_oper_chwidth == 1)
n_chans = 4;
/* TODO: VHT80+80, VHT160. Update acs_adjust_vht_center_freq() too. */
wpa_printf(MSG_DEBUG, "ACS: Survey analysis for selected bandwidth %d MHz",
n_chans == 1 ? 20 :
n_chans == 2 ? 40 :
n_chans == 4 ? 80 :
-1);
for (i = 0; i < iface->current_mode->num_channels; i++) {
chan = &iface->current_mode->channels[i];
if (!acs_usable_chan(chan))
continue;
/* HT40 on 5 GHz has a limited set of primary channels as per
* 11n Annex J */
if (iface->current_mode->mode == HOSTAPD_MODE_IEEE80211A &&
iface->conf->ieee80211n &&
iface->conf->secondary_channel &&
!acs_usable_ht40_chan(chan)) {
wpa_printf(MSG_DEBUG, "ACS: Channel %d: not allowed as primary channel for HT40",
chan->chan);
continue;
}
factor = chan->interference_factor;
for (j = 1; j < n_chans; j++) {
adj_chan = acs_find_chan(iface, chan->freq + (j * 20));
if (!adj_chan)
break;
factor += adj_chan->interference_factor;
}
if (j != n_chans) {
wpa_printf(MSG_DEBUG, "ACS: Channel %d: not enough bandwidth",
chan->chan);
continue;
}
/* 2.4 GHz has overlapping 20 MHz channels. Include adjacent
* channel interference factor. */
if (iface->current_mode->mode == HOSTAPD_MODE_IEEE80211B ||
iface->current_mode->mode == HOSTAPD_MODE_IEEE80211G) {
for (j = 0; j < n_chans; j++) {
/* TODO: perhaps a multiplier should be used
* here? */
adj_chan = acs_find_chan(iface, chan->freq +
(j * 20) - 5);
if (adj_chan)
factor += adj_chan->interference_factor;
adj_chan = acs_find_chan(iface, chan->freq +
(j * 20) - 10);
if (adj_chan)
factor += adj_chan->interference_factor;
adj_chan = acs_find_chan(iface, chan->freq +
(j * 20) + 5);
if (adj_chan)
factor += adj_chan->interference_factor;
adj_chan = acs_find_chan(iface, chan->freq +
(j * 20) + 10);
if (adj_chan)
factor += adj_chan->interference_factor;
}
}
wpa_printf(MSG_DEBUG, "ACS: * channel %d: total interference = %Lg",
chan->chan, factor);
if (!ideal_chan || factor < ideal_factor) {
ideal_factor = factor;
ideal_chan = chan;
}
}
if (ideal_chan)
wpa_printf(MSG_DEBUG, "ACS: Ideal channel is %d (%d MHz) with total interference factor of %Lg",
ideal_chan->chan, ideal_chan->freq, ideal_factor);
return ideal_chan;
}
static void acs_adjust_vht_center_freq(struct hostapd_iface *iface)
{
wpa_printf(MSG_DEBUG, "ACS: Adjusting VHT center frequency");
switch (iface->conf->vht_oper_chwidth) {
case VHT_CHANWIDTH_USE_HT:
iface->conf->vht_oper_centr_freq_seg0_idx =
iface->conf->channel + 2;
break;
case VHT_CHANWIDTH_80MHZ:
iface->conf->vht_oper_centr_freq_seg0_idx =
iface->conf->channel + 6;
break;
default:
/* TODO: How can this be calculated? Adjust
* acs_find_ideal_chan() */
wpa_printf(MSG_INFO, "ACS: Only VHT20/40/80 is supported now");
break;
}
}
static int acs_study_survey_based(struct hostapd_iface *iface)
{
wpa_printf(MSG_DEBUG, "ACS: Trying survey-based ACS");
if (!iface->chans_surveyed) {
wpa_printf(MSG_ERROR, "ACS: Unable to collect survey data");
return -1;
}
if (!acs_surveys_are_sufficient(iface)) {
wpa_printf(MSG_ERROR, "ACS: Surveys have insufficient data");
return -1;
}
acs_survey_all_chans_intereference_factor(iface);
return 0;
}
static int acs_study_options(struct hostapd_iface *iface)
{
int err;
err = acs_study_survey_based(iface);
if (err == 0)
return 0;
/* TODO: If no surveys are available/sufficient this is a good
* place to fallback to BSS-based ACS */
return -1;
}
static void acs_study(struct hostapd_iface *iface)
{
struct hostapd_channel_data *ideal_chan;
int err;
err = acs_study_options(iface);
if (err < 0) {
wpa_printf(MSG_ERROR, "ACS: All study options have failed");
goto fail;
}
ideal_chan = acs_find_ideal_chan(iface);
if (!ideal_chan) {
wpa_printf(MSG_ERROR, "ACS: Failed to compute ideal channel");
goto fail;
}
iface->conf->channel = ideal_chan->chan;
if (iface->conf->ieee80211ac)
acs_adjust_vht_center_freq(iface);
/*
* hostapd_setup_interface_complete() will return -1 on failure,
* 0 on success and 0 is HOSTAPD_CHAN_VALID :)
*/
switch (hostapd_acs_completed(iface)) {
case HOSTAPD_CHAN_VALID:
acs_cleanup(iface);
return;
case HOSTAPD_CHAN_INVALID:
case HOSTAPD_CHAN_ACS:
default:
/* This can possibly happen if channel parameters (secondary
* channel, center frequencies) are misconfigured */
wpa_printf(MSG_ERROR, "ACS: Possibly channel configuration is invalid, please report this along with your config file.");
goto fail;
}
fail:
acs_fail(iface);
}
static void acs_scan_complete(struct hostapd_iface *iface)
{
int err;
iface->scan_cb = NULL;
wpa_printf(MSG_DEBUG, "ACS: Using survey based algorithm (acs_num_scans=%d)",
iface->conf->acs_num_scans);
err = hostapd_drv_get_survey(iface->bss[0], 0);
if (err) {
wpa_printf(MSG_ERROR, "ACS: Failed to get survey data");
acs_fail(iface);
}
if (++iface->acs_num_completed_scans < iface->conf->acs_num_scans) {
err = acs_request_scan(iface);
if (err) {
wpa_printf(MSG_ERROR, "ACS: Failed to request scan");
acs_fail(iface);
return;
}
return;
}
acs_study(iface);
}
static int acs_request_scan(struct hostapd_iface *iface)
{
struct wpa_driver_scan_params params;
struct hostapd_channel_data *chan;
int i, *freq;
os_memset(&params, 0, sizeof(params));
params.freqs = os_calloc(iface->current_mode->num_channels + 1,
sizeof(params.freqs[0]));
if (params.freqs == NULL)
return -1;
freq = params.freqs;
for (i = 0; i < iface->current_mode->num_channels; i++) {
chan = &iface->current_mode->channels[i];
if (chan->flag & HOSTAPD_CHAN_DISABLED)
continue;
*freq++ = chan->freq;
}
*freq = 0;
iface->scan_cb = acs_scan_complete;
wpa_printf(MSG_DEBUG, "ACS: Scanning %d / %d",
iface->acs_num_completed_scans + 1,
iface->conf->acs_num_scans);
if (hostapd_driver_scan(iface->bss[0], &params) < 0) {
wpa_printf(MSG_ERROR, "ACS: Failed to request initial scan");
acs_cleanup(iface);
return -1;
}
os_free(params.freqs);
return 0;
}
enum hostapd_chan_status acs_init(struct hostapd_iface *iface)
{
int err;
wpa_printf(MSG_INFO, "ACS: Automatic channel selection started, this may take a bit");
acs_cleanup(iface);
err = acs_request_scan(iface);
if (err < 0)
return HOSTAPD_CHAN_INVALID;
return HOSTAPD_CHAN_ACS;
}

28
src/ap/acs.h Normal file
View file

@ -0,0 +1,28 @@
/*
* ACS - Automatic Channel Selection module
* Copyright (c) 2011, Atheros Communications
* Copyright (c) 2013, Qualcomm Atheros, Inc.
*
* This software may be distributed under the terms of the BSD license.
* See README for more details.
*/
#ifndef ACS_H
#define ACS_H
#ifdef CONFIG_ACS
enum hostapd_chan_status acs_init(struct hostapd_iface *iface);
int hostapd_acs_completed(struct hostapd_iface *iface);
#else /* CONFIG_ACS */
static inline enum hostapd_chan_status acs_init(struct hostapd_iface *iface)
{
wpa_printf(MSG_ERROR, "ACS was disabled on your build, rebuild hostapd with CONFIG_ACS=y or set channel");
return HOSTAPD_CHAN_INVALID;
}
#endif /* CONFIG_ACS */
#endif /* ACS_H */

4
src/ap/ap_config.c
View file

@ -171,6 +171,10 @@ struct hostapd_config * hostapd_config_defaults(void)
conf->corrupt_gtk_rekey_mic_probability = 0.0d;
#endif /* CONFIG_TESTING_OPTIONS */
#ifdef CONFIG_ACS
conf->acs_num_scans = 5;
#endif /* CONFIG_ACS */
return conf;
}

4
src/ap/ap_config.h
View file

@ -532,6 +532,10 @@ struct hostapd_config {
double ignore_reassoc_probability;
double corrupt_gtk_rekey_mic_probability;
#endif /* CONFIG_TESTING_OPTIONS */
#ifdef CONFIG_ACS
unsigned int acs_num_scans;
#endif /* CONFIG_ACS */
};

4
src/ap/hostapd.c
View file

@ -919,6 +919,10 @@ static int setup_interface(struct hostapd_iface *iface)
"channel. (%d)", ret);
return -1;
}
if (ret == 1) {
wpa_printf(MSG_DEBUG, "Interface initialization will be completed in a callback (ACS)");
return 0;
}
ret = hostapd_check_ht_capab(iface);
if (ret < 0)
return -1;

4
src/ap/hostapd.h
View file

@ -310,6 +310,10 @@ struct hostapd_iface {
/* lowest observed noise floor in dBm */
s8 lowest_nf;
#ifdef CONFIG_ACS
unsigned int acs_num_completed_scans;
#endif /* CONFIG_ACS */
void (*scan_cb)(struct hostapd_iface *iface);
};

48
src/ap/hw_features.c
View file

@ -24,6 +24,7 @@
#include "hostapd.h"
#include "ap_config.h"
#include "ap_drv_ops.h"
#include "acs.h"
#include "hw_features.h"
@ -686,10 +687,18 @@ hostapd_check_chans(struct hostapd_iface *iface)
}
/*
* The user set channel=0 which is used to trigger ACS,
* which we do not yet support.
* The user set channel=0 or channel=acs_survey
* which is used to trigger ACS.
*/
return HOSTAPD_CHAN_INVALID;
switch (acs_init(iface)) {
case HOSTAPD_CHAN_ACS:
return HOSTAPD_CHAN_ACS;
case HOSTAPD_CHAN_VALID:
case HOSTAPD_CHAN_INVALID:
default:
return HOSTAPD_CHAN_INVALID;
}
}
@ -709,6 +718,36 @@ static void hostapd_notify_bad_chans(struct hostapd_iface *iface)
}
int hostapd_acs_completed(struct hostapd_iface *iface)
{
int ret;
switch (hostapd_check_chans(iface)) {
case HOSTAPD_CHAN_VALID:
break;
case HOSTAPD_CHAN_ACS:
wpa_printf(MSG_ERROR, "ACS error - reported complete, but no result available");
hostapd_notify_bad_chans(iface);
return -1;
case HOSTAPD_CHAN_INVALID:
default:
wpa_printf(MSG_ERROR, "ACS picked unusable channels");
hostapd_notify_bad_chans(iface);
return -1;
}
ret = hostapd_check_ht_capab(iface);
if (ret < 0)
return -1;
if (ret == 1) {
wpa_printf(MSG_DEBUG, "Interface initialization will be completed in a callback");
return 0;
}
return hostapd_setup_interface_complete(iface, 0);
}
/**
* hostapd_select_hw_mode - Select the hardware mode
* @iface: Pointer to interface data.
@ -747,7 +786,8 @@ int hostapd_select_hw_mode(struct hostapd_iface *iface)
switch (hostapd_check_chans(iface)) {
case HOSTAPD_CHAN_VALID:
return 0;
case HOSTAPD_CHAN_ACS: /* ACS not supported yet */
case HOSTAPD_CHAN_ACS: /* ACS will run and later complete */
return 1;
case HOSTAPD_CHAN_INVALID:
default:
hostapd_notify_bad_chans(iface);

10
src/drivers/driver.h
View file

@ -29,6 +29,7 @@
#define HOSTAPD_CHAN_HT40PLUS 0x00000010
#define HOSTAPD_CHAN_HT40MINUS 0x00000020
#define HOSTAPD_CHAN_HT40 0x00000040
#define HOSTAPD_CHAN_SURVEY_LIST_INITIALIZED 0x00000080
#define HOSTAPD_CHAN_DFS_UNKNOWN 0x00000000
#define HOSTAPD_CHAN_DFS_USABLE 0x00000100
@ -70,6 +71,15 @@ struct hostapd_channel_data {
* surveyed channel data
*/
s8 min_nf;
#ifdef CONFIG_ACS
/**
* interference_factor - Computed interference factor on this
* channel (used internally in src/ap/acs.c; driver wrappers do not
* need to set this)
*/
long double interference_factor;
#endif /* CONFIG_ACS */
};
#define HOSTAPD_MODE_FLAG_HT_INFO_KNOWN BIT(0)