/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2002-2009 Sam Leffler, Errno Consulting
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
/*
 * IEEE 802.11 station scanning support.
 */
#include "opt_wlan.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/endian.h>
#include <sys/malloc.h>
#include <sys/module.h>

#include <sys/socket.h>

#include <net/if.h>
#include <net/if_var.h>
#include <net/if_media.h>
#include <net/ethernet.h>

#include <net80211/ieee80211_var.h>
#include <net80211/ieee80211_input.h>
#include <net80211/ieee80211_regdomain.h>
#ifdef IEEE80211_SUPPORT_TDMA
#include <net80211/ieee80211_tdma.h>
#endif
#ifdef IEEE80211_SUPPORT_MESH
#include <net80211/ieee80211_mesh.h>
#endif
#include <net80211/ieee80211_ratectl.h>
#include <net80211/ieee80211_vht.h>

#include <net/bpf.h>

/*
 * Parameters for managing cache entries:
 *
 * o a station with STA_FAILS_MAX failures is not considered
 *   when picking a candidate
 * o a station that hasn't had an update in STA_PURGE_SCANS
 *   (background) scans is discarded
 * o after STA_FAILS_AGE seconds we clear the failure count
 */
#define STA_FAILS_MAX   2               /* assoc failures before ignored */
#define STA_FAILS_AGE   (2*60)          /* time before clearing fails (secs) */
#define STA_PURGE_SCANS 2               /* age for purging entries (scans) */

/* XXX tunable */
#define STA_RSSI_MIN    8               /* min acceptable rssi */
#define STA_RSSI_MAX    40              /* max rssi for comparison */

struct sta_entry {
        struct ieee80211_scan_entry base;
        TAILQ_ENTRY(sta_entry) se_list;
        LIST_ENTRY(sta_entry) se_hash;
        uint8_t         se_fails;               /* failure to associate count */
        uint8_t         se_seen;                /* seen during current scan */
        uint8_t         se_notseen;             /* not seen in previous scans */
        uint8_t         se_flags;
#define STA_DEMOTE11B   0x01                    /* match w/ demoted 11b chan */
        uint32_t        se_avgrssi;             /* LPF rssi state */
        unsigned long   se_lastupdate;          /* time of last update */
        unsigned long   se_lastfail;            /* time of last failure */
        unsigned long   se_lastassoc;           /* time of last association */
        u_int           se_scangen;             /* iterator scan gen# */
        u_int           se_countrygen;          /* gen# of last cc notify */
};

#define STA_HASHSIZE    32
/* simple hash is enough for variation of macaddr */
#define STA_HASH(addr)  \
        (((const uint8_t *)(addr))[IEEE80211_ADDR_LEN - 1] % STA_HASHSIZE)

#define MAX_IEEE_CHAN   256                     /* max acceptable IEEE chan # */
CTASSERT(MAX_IEEE_CHAN >= 256);

struct sta_table {
        ieee80211_scan_table_lock_t st_lock;    /* on scan table */
        TAILQ_HEAD(, sta_entry) st_entry;       /* all entries */
        LIST_HEAD(, sta_entry) st_hash[STA_HASHSIZE];
        ieee80211_scan_iter_lock_t st_scanlock;         /* on st_scaniter */
        u_int           st_scaniter;            /* gen# for iterator */
        u_int           st_scangen;             /* scan generation # */
        int             st_newscan;
        /* ap-related state */
        int             st_maxrssi[MAX_IEEE_CHAN];
};

static void sta_flush_table(struct sta_table *);
/*
 * match_bss returns a bitmask describing if an entry is suitable
 * for use.  If non-zero the entry was deemed not suitable and it's
 * contents explains why.  The following flags are or'd to this
 * mask and can be used to figure out why the entry was rejected.
 */
#define MATCH_CHANNEL           0x00001 /* channel mismatch */
#define MATCH_CAPINFO           0x00002 /* capabilities mismatch, e.g. no ess */
#define MATCH_PRIVACY           0x00004 /* privacy mismatch */
#define MATCH_RATE              0x00008 /* rate set mismatch */
#define MATCH_SSID              0x00010 /* ssid mismatch */
#define MATCH_BSSID             0x00020 /* bssid mismatch */
#define MATCH_FAILS             0x00040 /* too many failed auth attempts */
#define MATCH_NOTSEEN           0x00080 /* not seen in recent scans */
#define MATCH_RSSI              0x00100 /* rssi deemed too low to use */
#define MATCH_CC                0x00200 /* country code mismatch */
#ifdef IEEE80211_SUPPORT_TDMA
#define MATCH_TDMA_NOIE         0x00400 /* no TDMA ie */
#define MATCH_TDMA_NOTMASTER    0x00800 /* not TDMA master */
#define MATCH_TDMA_NOSLOT       0x01000 /* all TDMA slots occupied */
#define MATCH_TDMA_LOCAL        0x02000 /* local address */
#define MATCH_TDMA_VERSION      0x04000 /* protocol version mismatch */
#endif
#define MATCH_MESH_NOID         0x10000 /* no MESHID ie */
#define MATCH_MESHID            0x20000 /* meshid mismatch */
static int match_bss(struct ieee80211vap *,
        const struct ieee80211_scan_state *, struct sta_entry *, int);
static void adhoc_age(struct ieee80211_scan_state *);

static __inline int
isocmp(const uint8_t cc1[], const uint8_t cc2[])
{
     return (cc1[0] == cc2[0] && cc1[1] == cc2[1]);
}

/* number of references from net80211 layer */
static  int nrefs = 0;
/*
 * Module glue.
 */
IEEE80211_SCANNER_MODULE(sta, 1);

/*
 * Attach prior to any scanning work.
 */
static int
sta_attach(struct ieee80211_scan_state *ss)
{
        struct sta_table *st;

        st = (struct sta_table *) IEEE80211_MALLOC(sizeof(struct sta_table),
                M_80211_SCAN,
                IEEE80211_M_NOWAIT | IEEE80211_M_ZERO);
        if (st == NULL)
                return 0;
        IEEE80211_SCAN_TABLE_LOCK_INIT(st, "scantable");
        IEEE80211_SCAN_ITER_LOCK_INIT(st, "scangen");
        TAILQ_INIT(&st->st_entry);
        ss->ss_priv = st;
        nrefs++;                        /* NB: we assume caller locking */
        return 1;
}

/*
 * Cleanup any private state.
 */
static int
sta_detach(struct ieee80211_scan_state *ss)
{
        struct sta_table *st = ss->ss_priv;

        if (st != NULL) {
                sta_flush_table(st);
                IEEE80211_SCAN_TABLE_LOCK_DESTROY(st);
                IEEE80211_SCAN_ITER_LOCK_DESTROY(st);
                IEEE80211_FREE(st, M_80211_SCAN);
                KASSERT(nrefs > 0, ("imbalanced attach/detach"));
                nrefs--;                /* NB: we assume caller locking */
        }
        return 1;
}

/*
 * Flush all per-scan state.
 */
static int
sta_flush(struct ieee80211_scan_state *ss)
{
        struct sta_table *st = ss->ss_priv;

        IEEE80211_SCAN_TABLE_LOCK(st);
        sta_flush_table(st);
        IEEE80211_SCAN_TABLE_UNLOCK(st);
        ss->ss_last = 0;
        return 0;
}

/*
 * Flush all entries in the scan cache.
 */
static void
sta_flush_table(struct sta_table *st)
{
        struct sta_entry *se, *next;

        TAILQ_FOREACH_SAFE(se, &st->st_entry, se_list, next) {
                TAILQ_REMOVE(&st->st_entry, se, se_list);
                LIST_REMOVE(se, se_hash);
                ieee80211_ies_cleanup(&se->base.se_ies);
                IEEE80211_FREE(se, M_80211_SCAN);
        }
        memset(st->st_maxrssi, 0, sizeof(st->st_maxrssi));
}

/*
 * Process a beacon or probe response frame; create an
 * entry in the scan cache or update any previous entry.
 */
static int
sta_add(struct ieee80211_scan_state *ss, 
        struct ieee80211_channel *curchan,
        const struct ieee80211_scanparams *sp,
        const struct ieee80211_frame *wh,
        int subtype, int rssi, int noise)
{
#define ISPROBE(_st)    ((_st) == IEEE80211_FC0_SUBTYPE_PROBE_RESP)
#define PICK1ST(_ss) \
        ((ss->ss_flags & (IEEE80211_SCAN_PICK1ST | IEEE80211_SCAN_GOTPICK)) == \
        IEEE80211_SCAN_PICK1ST)
        struct sta_table *st = ss->ss_priv;
        const uint8_t *macaddr = wh->i_addr2;
        struct ieee80211vap *vap = ss->ss_vap;
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_channel *c;
        struct sta_entry *se;
        struct ieee80211_scan_entry *ise;
        int hash;

        hash = STA_HASH(macaddr);

        IEEE80211_SCAN_TABLE_LOCK(st);
        LIST_FOREACH(se, &st->st_hash[hash], se_hash)
                if (IEEE80211_ADDR_EQ(se->base.se_macaddr, macaddr))
                        goto found;
        se = (struct sta_entry *) IEEE80211_MALLOC(sizeof(struct sta_entry),
                M_80211_SCAN, IEEE80211_M_NOWAIT | IEEE80211_M_ZERO);
        if (se == NULL) {
                IEEE80211_SCAN_TABLE_UNLOCK(st);
                return 0;
        }
        se->se_scangen = st->st_scaniter-1;
        se->se_avgrssi = IEEE80211_RSSI_DUMMY_MARKER;
        IEEE80211_ADDR_COPY(se->base.se_macaddr, macaddr);
        TAILQ_INSERT_TAIL(&st->st_entry, se, se_list);
        LIST_INSERT_HEAD(&st->st_hash[hash], se, se_hash);
found:
        ise = &se->base;
        /* XXX ap beaconing multiple ssid w/ same bssid */
        if (sp->ssid[1] != 0 &&
            (ISPROBE(subtype) || ise->se_ssid[1] == 0))
                memcpy(ise->se_ssid, sp->ssid, 2+sp->ssid[1]);
        KASSERT(sp->rates[1] <= IEEE80211_RATE_MAXSIZE,
                ("rate set too large: %u", sp->rates[1]));
        memcpy(ise->se_rates, sp->rates, 2+sp->rates[1]);
        if (sp->xrates != NULL) {
                /* XXX validate xrates[1] */
                KASSERT(sp->xrates[1] <= IEEE80211_RATE_MAXSIZE,
                        ("xrate set too large: %u", sp->xrates[1]));
                memcpy(ise->se_xrates, sp->xrates, 2+sp->xrates[1]);
        } else
                ise->se_xrates[1] = 0;
        IEEE80211_ADDR_COPY(ise->se_bssid, wh->i_addr3);
        if ((sp->status & IEEE80211_BPARSE_OFFCHAN) == 0) {
                /*
                 * Record rssi data using extended precision LPF filter.
                 *
                 * NB: use only on-channel data to insure we get a good
                 *     estimate of the signal we'll see when associated.
                 */
                IEEE80211_RSSI_LPF(se->se_avgrssi, rssi);
                ise->se_rssi = IEEE80211_RSSI_GET(se->se_avgrssi);
                ise->se_noise = noise;
        }
        memcpy(ise->se_tstamp.data, sp->tstamp, sizeof(ise->se_tstamp));
        ise->se_intval = sp->bintval;
        ise->se_capinfo = sp->capinfo;
#ifdef IEEE80211_SUPPORT_MESH
        if (sp->meshid != NULL && sp->meshid[1] != 0)
                memcpy(ise->se_meshid, sp->meshid, 2+sp->meshid[1]);
#endif
        /*
         * Beware of overriding se_chan for frames seen
         * off-channel; this can cause us to attempt an
         * association on the wrong channel.
         */
        if (sp->status & IEEE80211_BPARSE_OFFCHAN) {
                /*
                 * Off-channel, locate the home/bss channel for the sta
                 * using the value broadcast in the DSPARMS ie.  We know
                 * sp->chan has this value because it's used to calculate
                 * IEEE80211_BPARSE_OFFCHAN.
                 */
                c = ieee80211_find_channel_byieee(ic, sp->chan,
                    curchan->ic_flags);
                if (c != NULL) {
                        ise->se_chan = c;
                } else if (ise->se_chan == NULL) {
                        /* should not happen, pick something */
                        ise->se_chan = curchan;
                }
        } else
                ise->se_chan = curchan;

        /* VHT demotion */
        if (IEEE80211_IS_CHAN_VHT(ise->se_chan) && sp->vhtcap == NULL) {
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_11N,
                    "%s: demoting VHT->HT %d/0x%08x\n",
                    __func__, ise->se_chan->ic_freq, ise->se_chan->ic_flags);
                /* Demote legacy networks to a non-VHT channel. */
                c = ieee80211_find_channel(ic, ise->se_chan->ic_freq,
                    ise->se_chan->ic_flags & ~IEEE80211_CHAN_VHT);
                KASSERT(c != NULL,
                    ("no non-VHT channel %u", ise->se_chan->ic_ieee));
                ise->se_chan = c;
        }

        /* HT demotion */
        if (IEEE80211_IS_CHAN_HT(ise->se_chan) && sp->htcap == NULL) {
                /* Demote legacy networks to a non-HT channel. */
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_11N,
                    "%s: demoting HT->legacy %d/0x%08x\n",
                    __func__, ise->se_chan->ic_freq, ise->se_chan->ic_flags);
                c = ieee80211_find_channel(ic, ise->se_chan->ic_freq,
                    ise->se_chan->ic_flags & ~IEEE80211_CHAN_HT);
                KASSERT(c != NULL,
                    ("no legacy channel %u", ise->se_chan->ic_ieee));
                ise->se_chan = c;
        }

        ise->se_fhdwell = sp->fhdwell;
        ise->se_fhindex = sp->fhindex;
        ise->se_erp = sp->erp;
        ise->se_timoff = sp->timoff;
        if (sp->tim != NULL) {
                const struct ieee80211_tim_ie *tim =
                    (const struct ieee80211_tim_ie *) sp->tim;
                ise->se_dtimperiod = tim->tim_period;
        }
        if (sp->country != NULL) {
                const struct ieee80211_country_ie *cie =
                    (const struct ieee80211_country_ie *) sp->country;
                /*
                 * If 11d is enabled and we're attempting to join a bss
                 * that advertises it's country code then compare our
                 * current settings to what we fetched from the country ie.
                 * If our country code is unspecified or different then
                 * dispatch an event to user space that identifies the
                 * country code so our regdomain config can be changed.
                 */
                /* XXX only for STA mode? */
                if ((IEEE80211_IS_CHAN_11D(ise->se_chan) ||
                    (vap->iv_flags_ext & IEEE80211_FEXT_DOTD)) &&
                    (ic->ic_regdomain.country == CTRY_DEFAULT ||
                     !isocmp(cie->cc, ic->ic_regdomain.isocc))) {
                        /* only issue one notify event per scan */
                        if (se->se_countrygen != st->st_scangen) {
                                ieee80211_notify_country(vap, ise->se_bssid,
                                    cie->cc);
                                se->se_countrygen = st->st_scangen;
                        }
                }
                ise->se_cc[0] = cie->cc[0];
                ise->se_cc[1] = cie->cc[1];
        }
        /* NB: no need to setup ie ptrs; they are not (currently) used */
        (void) ieee80211_ies_init(&ise->se_ies, sp->ies, sp->ies_len);

        /* clear failure count after STA_FAIL_AGE passes */
        if (se->se_fails && (ticks - se->se_lastfail) > STA_FAILS_AGE*hz) {
                se->se_fails = 0;
                IEEE80211_NOTE_MAC(vap, IEEE80211_MSG_SCAN, macaddr,
                    "%s: fails %u", __func__, se->se_fails);
        }

        se->se_lastupdate = ticks;              /* update time */
        se->se_seen = 1;
        se->se_notseen = 0;

        KASSERT(sizeof(sp->bchan) == 1, ("bchan size"));
        if (rssi > st->st_maxrssi[sp->bchan])
                st->st_maxrssi[sp->bchan] = rssi;

        IEEE80211_SCAN_TABLE_UNLOCK(st);

        /*
         * If looking for a quick choice and nothing's
         * been found check here.
         */
        if (PICK1ST(ss) && match_bss(vap, ss, se, IEEE80211_MSG_SCAN) == 0)
                ss->ss_flags |= IEEE80211_SCAN_GOTPICK;

        return 1;
#undef PICK1ST
#undef ISPROBE
}

/*
 * Check if a channel is excluded by user request.
 */
static int
isexcluded(struct ieee80211vap *vap, const struct ieee80211_channel *c)
{
        return (isclr(vap->iv_ic->ic_chan_active, c->ic_ieee) ||
            (vap->iv_des_chan != IEEE80211_CHAN_ANYC &&
             c->ic_freq != vap->iv_des_chan->ic_freq));
}

static struct ieee80211_channel *
find11gchannel(struct ieee80211com *ic, int i, int freq)
{
        struct ieee80211_channel *c;
        int j;

        /*
         * The normal ordering in the channel list is b channel
         * immediately followed by g so optimize the search for
         * this.  We'll still do a full search just in case.
         */
        for (j = i+1; j < ic->ic_nchans; j++) {
                c = &ic->ic_channels[j];
                if (c->ic_freq == freq && IEEE80211_IS_CHAN_G(c))
                        return c;
        }
        for (j = 0; j < i; j++) {
                c = &ic->ic_channels[j];
                if (c->ic_freq == freq && IEEE80211_IS_CHAN_G(c))
                        return c;
        }
        return NULL;
}

static const u_int chanflags[IEEE80211_MODE_MAX] = {
        [IEEE80211_MODE_AUTO]     = IEEE80211_CHAN_B,
        [IEEE80211_MODE_11A]      = IEEE80211_CHAN_A,
        [IEEE80211_MODE_11B]      = IEEE80211_CHAN_B,
        [IEEE80211_MODE_11G]      = IEEE80211_CHAN_G,
        [IEEE80211_MODE_FH]       = IEEE80211_CHAN_FHSS,
        /* check base channel */
        [IEEE80211_MODE_TURBO_A]  = IEEE80211_CHAN_A,
        [IEEE80211_MODE_TURBO_G]  = IEEE80211_CHAN_G,
        [IEEE80211_MODE_STURBO_A] = IEEE80211_CHAN_ST,
        [IEEE80211_MODE_HALF]     = IEEE80211_CHAN_HALF,
        [IEEE80211_MODE_QUARTER]  = IEEE80211_CHAN_QUARTER,
        /* check legacy */
        [IEEE80211_MODE_11NA]     = IEEE80211_CHAN_A,
        [IEEE80211_MODE_11NG]     = IEEE80211_CHAN_G,
        [IEEE80211_MODE_VHT_5GHZ] = IEEE80211_CHAN_A,
        [IEEE80211_MODE_VHT_2GHZ] = IEEE80211_CHAN_G,
};

static void
add_channels(struct ieee80211vap *vap,
        struct ieee80211_scan_state *ss,
        enum ieee80211_phymode mode, const uint16_t freq[], int nfreq)
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_channel *c, *cg;
        u_int modeflags;
        int i;

        KASSERT(mode < nitems(chanflags), ("Unexpected mode %u", mode));
        modeflags = chanflags[mode];
        for (i = 0; i < nfreq; i++) {
                if (ss->ss_last >= IEEE80211_SCAN_MAX)
                        break;

                c = ieee80211_find_channel(ic, freq[i], modeflags);
                if (c == NULL || isexcluded(vap, c))
                        continue;
                if (mode == IEEE80211_MODE_AUTO) {
                        KASSERT(IEEE80211_IS_CHAN_B(c),
                            ("%s: wrong channel for 'auto' mode %u / %u\n",
                            __func__, c->ic_freq, c->ic_flags));

                        /*
                         * XXX special-case 11b/g channels so we select
                         *     the g channel if both are present.
                         */
                        if ((cg = find11gchannel(ic, i, c->ic_freq)) != NULL)
                                c = cg;
                }
                ss->ss_chans[ss->ss_last++] = c;
        }
}

struct scanlist {
        uint16_t        mode;
        uint16_t        count;
        const uint16_t  *list;
};

static int
checktable(const struct scanlist *scan, const struct ieee80211_channel *c)
{
        int i;

        for (; scan->list != NULL; scan++) {
                for (i = 0; i < scan->count; i++)
                        if (scan->list[i] == c->ic_freq) 
                                return 1;
        }
        return 0;
}

static int
onscanlist(const struct ieee80211_scan_state *ss,
        const struct ieee80211_channel *c)
{
        int i;

        for (i = 0; i < ss->ss_last; i++)
                if (ss->ss_chans[i] == c)
                        return 1;
        return 0;
}

static void
sweepchannels(struct ieee80211_scan_state *ss, struct ieee80211vap *vap,
        const struct scanlist table[])
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_channel *c;
        int i;

        for (i = 0; i < ic->ic_nchans; i++) {
                if (ss->ss_last >= IEEE80211_SCAN_MAX)
                        break;

                c = &ic->ic_channels[i];
                /*
                 * Ignore dynamic turbo channels; we scan them
                 * in normal mode (i.e. not boosted).  Likewise
                 * for HT/VHT channels, they get scanned using
                 * legacy rates.
                 */
                if (IEEE80211_IS_CHAN_DTURBO(c) || IEEE80211_IS_CHAN_HT(c) ||
                    IEEE80211_IS_CHAN_VHT(c))
                        continue;

                /*
                 * If a desired mode was specified, scan only 
                 * channels that satisfy that constraint.
                 */
                if (vap->iv_des_mode != IEEE80211_MODE_AUTO &&
                    vap->iv_des_mode != ieee80211_chan2mode(c))
                        continue;

                /*
                 * Skip channels excluded by user request.
                 */
                if (isexcluded(vap, c))
                        continue;

                /*
                 * Add the channel unless it is listed in the
                 * fixed scan order tables.  This insures we
                 * don't sweep back in channels we filtered out
                 * above.
                 */
                if (checktable(table, c))
                        continue;

                /* Add channel to scanning list. */
                ss->ss_chans[ss->ss_last++] = c;
        }
        /*
         * Explicitly add any desired channel if:
         * - not already on the scan list
         * - allowed by any desired mode constraint
         * - there is space in the scan list
         * This allows the channel to be used when the filtering
         * mechanisms would otherwise elide it (e.g HT, turbo).
         */
        c = vap->iv_des_chan;
        if (c != IEEE80211_CHAN_ANYC &&
            !onscanlist(ss, c) &&
            (vap->iv_des_mode == IEEE80211_MODE_AUTO ||
             vap->iv_des_mode == ieee80211_chan2mode(c)) &&
            ss->ss_last < IEEE80211_SCAN_MAX)
                ss->ss_chans[ss->ss_last++] = c;
}

static void
makescanlist(struct ieee80211_scan_state *ss, struct ieee80211vap *vap,
        const struct scanlist table[])
{
        const struct scanlist *scan;
        enum ieee80211_phymode mode;

        ss->ss_last = 0;
        /*
         * Use the table of ordered channels to construct the list
         * of channels for scanning.  Any channels in the ordered
         * list not in the master list will be discarded.
         */
        for (scan = table; scan->list != NULL; scan++) {
                mode = scan->mode;

                switch (mode) {
                case IEEE80211_MODE_11B:
                        if (vap->iv_des_mode == IEEE80211_MODE_11B)
                                break;

                        /*
                         * The scan table marks 2.4Ghz channels as b
                         * so if the desired mode is 11g / 11ng / 11acg,
                         * then use the 11b channel list but upgrade the mode.
                         *
                         * NB: 11b -> AUTO lets add_channels upgrade an
                         * 11b channel to 11g if available.
                         */
                        if (vap->iv_des_mode == IEEE80211_MODE_AUTO ||
                            vap->iv_des_mode == IEEE80211_MODE_11G ||
                            vap->iv_des_mode == IEEE80211_MODE_11NG ||
                            vap->iv_des_mode == IEEE80211_MODE_VHT_2GHZ) {
                                mode = vap->iv_des_mode;
                                break;
                        }

                        continue;
                case IEEE80211_MODE_11A:
                        /* Use 11a channel list for 11na / 11ac modes */
                        if (vap->iv_des_mode == IEEE80211_MODE_11NA ||
                            vap->iv_des_mode == IEEE80211_MODE_VHT_5GHZ) {
                                mode = vap->iv_des_mode;
                                break;
                        }

                        /* FALLTHROUGH */
                default:
                        /*
                         * If a desired mode was specified, scan only
                         * channels that satisfy that constraint.
                         */
                        if (vap->iv_des_mode != IEEE80211_MODE_AUTO &&
                            vap->iv_des_mode != mode)
                                continue;
                }

#ifdef IEEE80211_F_XR
                /* XR does not operate on turbo channels */
                if ((vap->iv_flags & IEEE80211_F_XR) &&
                    (mode == IEEE80211_MODE_TURBO_A ||
                     mode == IEEE80211_MODE_TURBO_G ||
                     mode == IEEE80211_MODE_STURBO_A))
                        continue;
#endif
                /*
                 * Add the list of the channels; any that are not
                 * in the master channel list will be discarded.
                 */
                add_channels(vap, ss, mode, scan->list, scan->count);
        }

        /*
         * Add the channels from the ic that are not present
         * in the table.
         */
        sweepchannels(ss, vap, table);
}

static const uint16_t rcl1[] =          /* 8 FCC channel: 52, 56, 60, 64, 36, 40, 44, 48 */
{ 5260, 5280, 5300, 5320, 5180, 5200, 5220, 5240 };
static const uint16_t rcl2[] =          /* 4 MKK channels: 34, 38, 42, 46 */
{ 5170, 5190, 5210, 5230 };
static const uint16_t rcl3[] =          /* 2.4Ghz ch: 1,6,11,7,13 */
{ 2412, 2437, 2462, 2442, 2472 };
static const uint16_t rcl4[] =          /* 5 FCC channel: 149, 153, 161, 165 */
{ 5745, 5765, 5785, 5805, 5825 };
static const uint16_t rcl7[] =          /* 11 ETSI channel: 100,104,108,112,116,120,124,128,132,136,140 */
{ 5500, 5520, 5540, 5560, 5580, 5600, 5620, 5640, 5660, 5680, 5700 };
static const uint16_t rcl8[] =          /* 2.4Ghz ch: 2,3,4,5,8,9,10,12 */
{ 2417, 2422, 2427, 2432, 2447, 2452, 2457, 2467 };
static const uint16_t rcl9[] =          /* 2.4Ghz ch: 14 */
{ 2484 };
static const uint16_t rcl10[] = /* Added Korean channels 2312-2372 */
{ 2312, 2317, 2322, 2327, 2332, 2337, 2342, 2347, 2352, 2357, 2362, 2367, 2372 };
static const uint16_t rcl11[] = /* Added Japan channels in 4.9/5.0 spectrum */
{ 5040, 5060, 5080, 4920, 4940, 4960, 4980 };
#ifdef ATH_TURBO_SCAN
static const uint16_t rcl5[] =          /* 3 static turbo channels */
{ 5210, 5250, 5290 };
static const uint16_t rcl6[] =          /* 2 static turbo channels */
{ 5760, 5800 };
static const uint16_t rcl6x[] = /* 4 FCC3 turbo channels */
{ 5540, 5580, 5620, 5660 };
static const uint16_t rcl12[] = /* 2.4Ghz Turbo channel 6 */
{ 2437 };
static const uint16_t rcl13[] = /* dynamic Turbo channels */
{ 5200, 5240, 5280, 5765, 5805 };
#endif /* ATH_TURBO_SCAN */

#define X(a)    .count = sizeof(a)/sizeof(a[0]), .list = a

static const struct scanlist staScanTable[] = {
        { IEEE80211_MODE_11B,           X(rcl3) },
        { IEEE80211_MODE_11A,           X(rcl1) },
        { IEEE80211_MODE_11A,           X(rcl2) },
        { IEEE80211_MODE_11B,           X(rcl8) },
        { IEEE80211_MODE_11B,           X(rcl9) },
        { IEEE80211_MODE_11A,           X(rcl4) },
#ifdef ATH_TURBO_SCAN
        { IEEE80211_MODE_STURBO_A,      X(rcl5) },
        { IEEE80211_MODE_STURBO_A,      X(rcl6) },
        { IEEE80211_MODE_TURBO_A,       X(rcl6x) },
        { IEEE80211_MODE_TURBO_A,       X(rcl13) },
#endif /* ATH_TURBO_SCAN */
        { IEEE80211_MODE_11A,           X(rcl7) },
        { IEEE80211_MODE_11B,           X(rcl10) },
        { IEEE80211_MODE_11A,           X(rcl11) },
#ifdef ATH_TURBO_SCAN
        { IEEE80211_MODE_TURBO_G,       X(rcl12) },
#endif /* ATH_TURBO_SCAN */
        { .list = NULL }
};

/*
 * Start a station-mode scan by populating the channel list.
 */
static int
sta_start(struct ieee80211_scan_state *ss, struct ieee80211vap *vap)
{
        struct sta_table *st = ss->ss_priv;

        makescanlist(ss, vap, staScanTable);

        if (ss->ss_mindwell == 0)
                ss->ss_mindwell = msecs_to_ticks(20);   /* 20ms */
        if (ss->ss_maxdwell == 0)
                ss->ss_maxdwell = msecs_to_ticks(200);  /* 200ms */

        st->st_scangen++;
        st->st_newscan = 1;

        return 0;
}

/*
 * Restart a scan, typically a bg scan but can
 * also be a fg scan that came up empty.
 */
static int
sta_restart(struct ieee80211_scan_state *ss, struct ieee80211vap *vap)
{
        struct sta_table *st = ss->ss_priv;

        st->st_newscan = 1;
        return 0;
}

/*
 * Cancel an ongoing scan.
 */
static int
sta_cancel(struct ieee80211_scan_state *ss, struct ieee80211vap *vap)
{
        return 0;
}

/*
 * Demote any supplied 11g channel to 11b.  There should
 * always be an 11b channel but we check anyway...
 */
static struct ieee80211_channel *
demote11b(struct ieee80211vap *vap, struct ieee80211_channel *chan)
{
        struct ieee80211_channel *c;

        if (IEEE80211_IS_CHAN_ANYG(chan) &&
            vap->iv_des_mode == IEEE80211_MODE_AUTO) {
                c = ieee80211_find_channel(vap->iv_ic, chan->ic_freq,
                    (chan->ic_flags &~ (IEEE80211_CHAN_PUREG | IEEE80211_CHAN_G)) |
                    IEEE80211_CHAN_B);
                if (c != NULL)
                        chan = c;
        }
        return chan;
}

static int
maxrate(const struct ieee80211_scan_entry *se)
{
        const struct ieee80211_ie_htcap *htcap =
            (const struct ieee80211_ie_htcap *) se->se_ies.htcap_ie;
        int rmax, r, i, txstream;
        uint16_t caps;
        uint8_t txparams;

        rmax = 0;
        if (htcap != NULL) {
                /*
                 * HT station; inspect supported MCS and then adjust
                 * rate by channel width.
                 */
                txparams = htcap->hc_mcsset[12];
                if (txparams & 0x3) {
                        /*
                         * TX MCS parameters defined and not equal to RX,
                         * extract the number of spartial streams and
                         * map it to the highest MCS rate.
                         */
                        txstream = ((txparams & 0xc) >> 2) + 1;
                        i = txstream * 8 - 1;
                } else
                        for (i = 31; i >= 0 && isclr(htcap->hc_mcsset, i); i--);
                if (i >= 0) {
                        caps = le16dec(&htcap->hc_cap);
                        if ((caps & IEEE80211_HTCAP_CHWIDTH40) &&
                            (caps & IEEE80211_HTCAP_SHORTGI40))
                                rmax = ieee80211_htrates[i].ht40_rate_400ns;
                        else if (caps & IEEE80211_HTCAP_CHWIDTH40)
                                rmax = ieee80211_htrates[i].ht40_rate_800ns;
                        else if (caps & IEEE80211_HTCAP_SHORTGI20)
                                rmax = ieee80211_htrates[i].ht20_rate_400ns;
                        else
                                rmax = ieee80211_htrates[i].ht20_rate_800ns;
                }
        }
        for (i = 0; i < se->se_rates[1]; i++) {
                r = se->se_rates[2+i] & IEEE80211_RATE_VAL;
                if (r > rmax)
                        rmax = r;
        }
        for (i = 0; i < se->se_xrates[1]; i++) {
                r = se->se_xrates[2+i] & IEEE80211_RATE_VAL;
                if (r > rmax)
                        rmax = r;
        }
        return rmax;
}

/*
 * Compare the capabilities of two entries and decide which is
 * more desirable (return >0 if a is considered better).  Note
 * that we assume compatibility/usability has already been checked
 * so we don't need to (e.g. validate whether privacy is supported).
 * Used to select the best scan candidate for association in a BSS.
 *
 * TODO: should we take 11n, 11ac into account when selecting the
 * best?  Right now it just compares frequency band and RSSI.
 */
static int
sta_compare(const struct sta_entry *a, const struct sta_entry *b)
{
#define PREFER(_a,_b,_what) do {                        \
        if (((_a) ^ (_b)) & (_what))                    \
                return ((_a) & (_what)) ? 1 : -1;       \
} while (0)
        int maxa, maxb;
        int8_t rssia, rssib;
        int weight;

        /* privacy support */
        PREFER(a->base.se_capinfo, b->base.se_capinfo,
                IEEE80211_CAPINFO_PRIVACY);

        /* compare count of previous failures */
        weight = b->se_fails - a->se_fails;
        if (abs(weight) > 1)
                return weight;

        /*
         * Compare rssi.  If the two are considered equivalent
         * then fallback to other criteria.  We threshold the
         * comparisons to avoid selecting an ap purely by rssi
         * when both values may be good but one ap is otherwise
         * more desirable (e.g. an 11b-only ap with stronger
         * signal than an 11g ap).
         */
        rssia = MIN(a->base.se_rssi, STA_RSSI_MAX);
        rssib = MIN(b->base.se_rssi, STA_RSSI_MAX);
        if (abs(rssib - rssia) < 5) {
                /* best/max rate preferred if signal level close enough XXX */
                maxa = maxrate(&a->base);
                maxb = maxrate(&b->base);
                if (maxa != maxb)
                        return maxa - maxb;
                /* XXX use freq for channel preference */
                /* for now just prefer 5Ghz band to all other bands */
                PREFER(IEEE80211_IS_CHAN_5GHZ(a->base.se_chan),
                       IEEE80211_IS_CHAN_5GHZ(b->base.se_chan), 1);
        }
        /* all things being equal, use signal level */
        return a->base.se_rssi - b->base.se_rssi;
#undef PREFER
}

/*
 * Check rate set suitability and return the best supported rate.
 * XXX inspect MCS for HT
 */
static int
check_rate(struct ieee80211vap *vap, const struct ieee80211_channel *chan,
    const struct ieee80211_scan_entry *se)
{
        const struct ieee80211_rateset *srs;
        int i, j, nrs, r, okrate, badrate, fixedrate, ucastrate;
        const uint8_t *rs;

        okrate = badrate = 0;

        srs = ieee80211_get_suprates(vap->iv_ic, chan);
        nrs = se->se_rates[1];
        rs = se->se_rates+2;
        /* XXX MCS */
        ucastrate = vap->iv_txparms[ieee80211_chan2mode(chan)].ucastrate;
        fixedrate = IEEE80211_FIXED_RATE_NONE;
again:
        for (i = 0; i < nrs; i++) {
                r = IEEE80211_RV(rs[i]);
                badrate = r;
                /*
                 * Check any fixed rate is included. 
                 */
                if (r == ucastrate)
                        fixedrate = r;
                /*
                 * Check against our supported rates.
                 */
                for (j = 0; j < srs->rs_nrates; j++)
                        if (r == IEEE80211_RV(srs->rs_rates[j])) {
                                if (r > okrate)         /* NB: track max */
                                        okrate = r;
                                break;
                        }

                if (j == srs->rs_nrates && (rs[i] & IEEE80211_RATE_BASIC)) {
                        /*
                         * Don't try joining a BSS, if we don't support
                         * one of its basic rates.
                         */
                        okrate = 0;
                        goto back;
                }
        }
        if (rs == se->se_rates+2) {
                /* scan xrates too; sort of an algol68-style for loop */
                nrs = se->se_xrates[1];
                rs = se->se_xrates+2;
                goto again;
        }

back:
        if (okrate == 0 || ucastrate != fixedrate)
                return badrate | IEEE80211_RATE_BASIC;
        else
                return IEEE80211_RV(okrate);
}

static __inline int
match_id(const uint8_t *ie, const uint8_t *val, int len)
{
        return (ie[1] == len && memcmp(ie+2, val, len) == 0);
}

static int
match_ssid(const uint8_t *ie,
        int nssid, const struct ieee80211_scan_ssid ssids[])
{
        int i;

        for (i = 0; i < nssid; i++) {
                if (match_id(ie, ssids[i].ssid, ssids[i].len))
                        return 1;
        }
        return 0;
}

#ifdef IEEE80211_SUPPORT_TDMA
static int
tdma_isfull(const struct ieee80211_tdma_param *tdma)
{
        int slot, slotcnt;

        slotcnt = tdma->tdma_slotcnt;
        for (slot = slotcnt-1; slot >= 0; slot--)
                if (isclr(tdma->tdma_inuse, slot))
                        return 0;
        return 1;
}
#endif /* IEEE80211_SUPPORT_TDMA */

/*
 * Test a scan candidate for suitability/compatibility.
 */
static int
match_bss(struct ieee80211vap *vap,
        const struct ieee80211_scan_state *ss, struct sta_entry *se0,
        int debug)
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_scan_entry *se = &se0->base;
        uint8_t rate;
        int fail;

        fail = 0;
        if (isclr(ic->ic_chan_active, ieee80211_chan2ieee(ic, se->se_chan)))
                fail |= MATCH_CHANNEL;
        /*
         * NB: normally the desired mode is used to construct
         * the channel list, but it's possible for the scan
         * cache to include entries for stations outside this
         * list so we check the desired mode here to weed them
         * out.
         */
        if (vap->iv_des_mode != IEEE80211_MODE_AUTO &&
            (se->se_chan->ic_flags & IEEE80211_CHAN_ALLTURBO) !=
            chanflags[vap->iv_des_mode])
                fail |= MATCH_CHANNEL;
        if (vap->iv_opmode == IEEE80211_M_IBSS) {
                if ((se->se_capinfo & IEEE80211_CAPINFO_IBSS) == 0)
                        fail |= MATCH_CAPINFO;
#ifdef IEEE80211_SUPPORT_TDMA
        } else if (vap->iv_opmode == IEEE80211_M_AHDEMO) {
                /*
                 * Adhoc demo network setup shouldn't really be scanning
                 * but just in case skip stations operating in IBSS or
                 * BSS mode.
                 */
                if (se->se_capinfo & (IEEE80211_CAPINFO_IBSS|IEEE80211_CAPINFO_ESS))
                        fail |= MATCH_CAPINFO;
                /*
                 * TDMA operation cannot coexist with a normal 802.11 network;
                 * skip if IBSS or ESS capabilities are marked and require
                 * the beacon have a TDMA ie present.
                 */
                if (vap->iv_caps & IEEE80211_C_TDMA) {
                        const struct ieee80211_tdma_param *tdma =
                            (const struct ieee80211_tdma_param *)se->se_ies.tdma_ie;
                        const struct ieee80211_tdma_state *ts = vap->iv_tdma;

                        if (tdma == NULL)
                                fail |= MATCH_TDMA_NOIE;
                        else if (tdma->tdma_version != ts->tdma_version)
                                fail |= MATCH_TDMA_VERSION;
                        else if (tdma->tdma_slot != 0)
                                fail |= MATCH_TDMA_NOTMASTER;
                        else if (tdma_isfull(tdma))
                                fail |= MATCH_TDMA_NOSLOT;
#if 0
                        else if (ieee80211_local_address(se->se_macaddr))
                                fail |= MATCH_TDMA_LOCAL;
#endif
                }
#endif /* IEEE80211_SUPPORT_TDMA */
#ifdef IEEE80211_SUPPORT_MESH
        } else if (vap->iv_opmode == IEEE80211_M_MBSS) {
                const struct ieee80211_mesh_state *ms = vap->iv_mesh;
                /*
                 * Mesh nodes have IBSS & ESS bits in capinfo turned off
                 * and two special ie's that must be present.
                 */
                if (se->se_capinfo & (IEEE80211_CAPINFO_IBSS|IEEE80211_CAPINFO_ESS))
                        fail |= MATCH_CAPINFO;
                else if (se->se_meshid[0] != IEEE80211_ELEMID_MESHID)
                        fail |= MATCH_MESH_NOID;
                else if (ms->ms_idlen != 0 &&
                    match_id(se->se_meshid, ms->ms_id, ms->ms_idlen))
                        fail |= MATCH_MESHID;
#endif
        } else {
                if ((se->se_capinfo & IEEE80211_CAPINFO_ESS) == 0)
                        fail |= MATCH_CAPINFO;
                /*
                 * If 11d is enabled and we're attempting to join a bss
                 * that advertises it's country code then compare our
                 * current settings to what we fetched from the country ie.
                 * If our country code is unspecified or different then do
                 * not attempt to join the bss.  We should have already
                 * dispatched an event to user space that identifies the
                 * new country code so our regdomain config should match.
                 */
                if ((IEEE80211_IS_CHAN_11D(se->se_chan) ||
                    (vap->iv_flags_ext & IEEE80211_FEXT_DOTD)) &&
                    se->se_cc[0] != 0 &&
                    (ic->ic_regdomain.country == CTRY_DEFAULT ||
                     !isocmp(se->se_cc, ic->ic_regdomain.isocc)))
                        fail |= MATCH_CC;
        }
        if (vap->iv_flags & IEEE80211_F_PRIVACY) {
                if ((se->se_capinfo & IEEE80211_CAPINFO_PRIVACY) == 0)
                        fail |= MATCH_PRIVACY;
        } else {
                /* XXX does this mean privacy is supported or required? */
                if (se->se_capinfo & IEEE80211_CAPINFO_PRIVACY)
                        fail |= MATCH_PRIVACY;
        }
        se0->se_flags &= ~STA_DEMOTE11B;
        rate = check_rate(vap, se->se_chan, se);
        if (rate & IEEE80211_RATE_BASIC) {
                fail |= MATCH_RATE;
                /*
                 * An 11b-only ap will give a rate mismatch if there is an
                 * OFDM fixed tx rate for 11g.  Try downgrading the channel
                 * in the scan list to 11b and retry the rate check.
                 */
                if (IEEE80211_IS_CHAN_ANYG(se->se_chan)) {
                        rate = check_rate(vap, demote11b(vap, se->se_chan), se);
                        if ((rate & IEEE80211_RATE_BASIC) == 0) {
                                fail &= ~MATCH_RATE;
                                se0->se_flags |= STA_DEMOTE11B;
                        }
                }
        } else if (rate < 2*24) {
                /*
                 * This is an 11b-only ap.  Check the desired mode in
                 * case that needs to be honored (mode 11g filters out
                 * 11b-only ap's).  Otherwise force any 11g channel used
                 * in scanning to be demoted.
                 *
                 * NB: we cheat a bit here by looking at the max rate;
                 *     we could/should check the rates.
                 */
                if (!(vap->iv_des_mode == IEEE80211_MODE_AUTO ||
                      vap->iv_des_mode == IEEE80211_MODE_11B))
                        fail |= MATCH_RATE;
                else
                        se0->se_flags |= STA_DEMOTE11B;
        }
        if (ss->ss_nssid != 0 &&
            !match_ssid(se->se_ssid, ss->ss_nssid, ss->ss_ssid))
                fail |= MATCH_SSID;
        if ((vap->iv_flags & IEEE80211_F_DESBSSID) &&
            !IEEE80211_ADDR_EQ(vap->iv_des_bssid, se->se_bssid))
                fail |= MATCH_BSSID;
        if (se0->se_fails >= STA_FAILS_MAX)
                fail |= MATCH_FAILS;
        if (se0->se_notseen >= STA_PURGE_SCANS)
                fail |= MATCH_NOTSEEN;
        if (se->se_rssi < STA_RSSI_MIN)
                fail |= MATCH_RSSI;
#ifdef IEEE80211_DEBUG
        if (ieee80211_msg(vap, debug)) {
                net80211_printf(" %c %s",
                    fail & MATCH_FAILS ? '=' :
                    fail & MATCH_NOTSEEN ? '^' :
                    fail & MATCH_CC ? '$' :
#ifdef IEEE80211_SUPPORT_TDMA
                    fail & MATCH_TDMA_NOIE ? '&' :
                    fail & MATCH_TDMA_VERSION ? 'v' :
                    fail & MATCH_TDMA_NOTMASTER ? 's' :
                    fail & MATCH_TDMA_NOSLOT ? 'f' :
                    fail & MATCH_TDMA_LOCAL ? 'l' :
#endif
                    fail & MATCH_MESH_NOID ? 'm' :
                    fail ? '-' : '+', ether_sprintf(se->se_macaddr));
                net80211_printf(" %s%c", ether_sprintf(se->se_bssid),
                    fail & MATCH_BSSID ? '!' : ' ');
                net80211_printf(" %3d%c", ieee80211_chan2ieee(ic, se->se_chan),
                        fail & MATCH_CHANNEL ? '!' : ' ');
                net80211_printf(" %+4d%c", se->se_rssi, fail & MATCH_RSSI ? '!' : ' ');
                net80211_printf(" %2dM%c", (rate & IEEE80211_RATE_VAL) / 2,
                    fail & MATCH_RATE ? '!' : ' ');
                net80211_printf(" %4s%c",
                    (se->se_capinfo & IEEE80211_CAPINFO_ESS) ? "ess" :
                    (se->se_capinfo & IEEE80211_CAPINFO_IBSS) ? "ibss" : "",
                    fail & MATCH_CAPINFO ? '!' : ' ');
                net80211_printf(" %3s%c ",
                    (se->se_capinfo & IEEE80211_CAPINFO_PRIVACY) ?
                    "wep" : "no",
                    fail & MATCH_PRIVACY ? '!' : ' ');
                ieee80211_print_essid(se->se_ssid+2, se->se_ssid[1]);
                net80211_printf("%s\n", fail & (MATCH_SSID | MATCH_MESHID) ? "!" : "");
        }
#endif
        return fail;
}

static void
sta_update_notseen(struct sta_table *st)
{
        struct sta_entry *se;

        IEEE80211_SCAN_TABLE_LOCK(st);
        TAILQ_FOREACH(se, &st->st_entry, se_list) {
                /*
                 * If seen the reset and don't bump the count;
                 * otherwise bump the ``not seen'' count.  Note
                 * that this insures that stations for which we
                 * see frames while not scanning but not during
                 * this scan will not be penalized.
                 */
                if (se->se_seen)
                        se->se_seen = 0;
                else
                        se->se_notseen++;
        }
        IEEE80211_SCAN_TABLE_UNLOCK(st);
}

static void
sta_dec_fails(struct sta_table *st)
{
        struct sta_entry *se;

        IEEE80211_SCAN_TABLE_LOCK(st);
        TAILQ_FOREACH(se, &st->st_entry, se_list)
                if (se->se_fails)
                        se->se_fails--;
        IEEE80211_SCAN_TABLE_UNLOCK(st);
}

static struct sta_entry *
select_bss(struct ieee80211_scan_state *ss, struct ieee80211vap *vap, int debug)
{
        struct sta_table *st = ss->ss_priv;
        struct sta_entry *se, *selbs = NULL;

        IEEE80211_DPRINTF(vap, debug, " %s\n",
            "macaddr          bssid         chan  rssi  rate flag  wep  essid");
        IEEE80211_SCAN_TABLE_LOCK(st);
        TAILQ_FOREACH(se, &st->st_entry, se_list) {
                ieee80211_ies_expand(&se->base.se_ies);
                if (match_bss(vap, ss, se, debug) == 0) {
                        if (selbs == NULL)
                                selbs = se;
                        else if (sta_compare(se, selbs) > 0)
                                selbs = se;
                }
        }
        IEEE80211_SCAN_TABLE_UNLOCK(st);

        return selbs;
}

/*
 * Pick an ap or ibss network to join or find a channel
 * to use to start an ibss network.
 */
static int
sta_pick_bss(struct ieee80211_scan_state *ss, struct ieee80211vap *vap)
{
        struct sta_table *st = ss->ss_priv;
        struct sta_entry *selbs;
        struct ieee80211_channel *chan;

        KASSERT(vap->iv_opmode == IEEE80211_M_STA,
                ("wrong mode %u", vap->iv_opmode));

        if (st->st_newscan) {
                sta_update_notseen(st);
                st->st_newscan = 0;
        }
        if (ss->ss_flags & IEEE80211_SCAN_NOPICK) {
                /*
                 * Manual/background scan, don't select+join the
                 * bss, just return.  The scanning framework will
                 * handle notification that this has completed.
                 */
                ss->ss_flags &= ~IEEE80211_SCAN_NOPICK;
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                    "%s: nopick; return 1\n", __func__);
                return 1;
        }
        /*
         * Automatic sequencing; look for a candidate and
         * if found join the network.
         */
        /* NB: unlocked read should be ok */
        if (TAILQ_FIRST(&st->st_entry) == NULL) {
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                        "%s: no scan candidate, join=%d, return 0\n",
                        __func__,
                        !! (ss->ss_flags & IEEE80211_SCAN_NOJOIN));
                if (ss->ss_flags & IEEE80211_SCAN_NOJOIN)
                        return 0;
notfound:
                /*
                 * If nothing suitable was found decrement
                 * the failure counts so entries will be
                 * reconsidered the next time around.  We
                 * really want to do this only for sta's
                 * where we've previously had some success.
                 */
                sta_dec_fails(st);
                st->st_newscan = 1;
                return 0;                       /* restart scan */
        }
        selbs = select_bss(ss, vap, IEEE80211_MSG_SCAN);
        if (ss->ss_flags & IEEE80211_SCAN_NOJOIN)
                return (selbs != NULL);
        if (selbs == NULL)
                goto notfound;
        chan = selbs->base.se_chan;
        if (selbs->se_flags & STA_DEMOTE11B)
                chan = demote11b(vap, chan);
        if (!ieee80211_sta_join(vap, chan, &selbs->base))
                goto notfound;
        IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
            "%s: terminate scan; return 1\n", __func__);
        return 1;                               /* terminate scan */
}

/*
 * Lookup an entry in the scan cache.  We assume we're
 * called from the bottom half or such that we don't need
 * to block the bottom half so that it's safe to return
 * a reference to an entry w/o holding the lock on the table.
 */
static struct sta_entry *
sta_lookup(struct sta_table *st, const uint8_t macaddr[IEEE80211_ADDR_LEN])
{
        struct sta_entry *se;
        int hash = STA_HASH(macaddr);

        IEEE80211_SCAN_TABLE_LOCK(st);
        LIST_FOREACH(se, &st->st_hash[hash], se_hash)
                if (IEEE80211_ADDR_EQ(se->base.se_macaddr, macaddr))
                        break;
        IEEE80211_SCAN_TABLE_UNLOCK(st);

        return se;              /* NB: unlocked */
}

static void
sta_roam_check(struct ieee80211_scan_state *ss, struct ieee80211vap *vap)
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_node *ni = vap->iv_bss;
        struct sta_table *st = ss->ss_priv;
        enum ieee80211_phymode mode;
        struct sta_entry *se, *selbs;
        uint8_t roamRate, curRate, ucastRate;
        int8_t roamRssi, curRssi;

        se = sta_lookup(st, ni->ni_macaddr);
        if (se == NULL) {
                /* XXX something is wrong */
                return;
        }

        mode = ieee80211_chan2mode(ic->ic_bsschan);
        roamRate = vap->iv_roamparms[mode].rate;
        roamRssi = vap->iv_roamparms[mode].rssi;
        KASSERT(roamRate != 0 && roamRssi != 0, ("iv_roamparms are not"
            "initialized for %s mode!", ieee80211_phymode_name[mode]));

        ucastRate = vap->iv_txparms[mode].ucastrate;
        /* NB: the most up to date rssi is in the node, not the scan cache */
        curRssi = ic->ic_node_getrssi(ni);
        if (ucastRate == IEEE80211_FIXED_RATE_NONE) {
                curRate = ieee80211_node_get_txrate_dot11rate(ni);
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_ROAM,
                    "%s: currssi %d currate %u roamrssi %d roamrate %u\n",
                    __func__, curRssi, curRate, roamRssi, roamRate);
        } else {
                curRate = roamRate;     /* NB: insure compare below fails */
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_ROAM,
                    "%s: currssi %d roamrssi %d\n", __func__, curRssi, roamRssi);
        }
        /*
         * Check if a new ap should be used and switch.
         * XXX deauth current ap
         */
        if (curRate < roamRate || curRssi < roamRssi) {
                if (ieee80211_time_after(ticks, ic->ic_lastscan + vap->iv_scanvalid)) {
                        /*
                         * Scan cache contents are too old; force a scan now
                         * if possible so we have current state to make a
                         * decision with.  We don't kick off a bg scan if
                         * we're using dynamic turbo and boosted or if the
                         * channel is busy.
                         * XXX force immediate switch on scan complete
                         */
                        if (!IEEE80211_IS_CHAN_DTURBO(ic->ic_curchan) &&
                            ((vap->iv_flags_ext & IEEE80211_FEXT_SCAN_OFFLOAD) ||
                             ieee80211_time_after(ticks, ic->ic_lastdata + vap->iv_bgscanidle)))
                                ieee80211_bg_scan(vap, 0);
                        return;
                }
                se->base.se_rssi = curRssi;
                selbs = select_bss(ss, vap, IEEE80211_MSG_ROAM);
                if (selbs != NULL && selbs != se) {
                        struct ieee80211_channel *chan;

                        IEEE80211_DPRINTF(vap,
                            IEEE80211_MSG_ROAM | IEEE80211_MSG_DEBUG,
                            "%s: ROAM: curRate %u, roamRate %u, "
                            "curRssi %d, roamRssi %d\n", __func__,
                            curRate, roamRate, curRssi, roamRssi);

                        chan = selbs->base.se_chan;
                        if (selbs->se_flags & STA_DEMOTE11B)
                                chan = demote11b(vap, chan);
                        (void) ieee80211_sta_join(vap, chan, &selbs->base);
                }
        }
}

/*
 * Age entries in the scan cache.
 * XXX also do roaming since it's convenient
 */
static void
sta_age(struct ieee80211_scan_state *ss)
{
        struct ieee80211vap *vap = ss->ss_vap;

        adhoc_age(ss);
        /*
         * If rate control is enabled check periodically to see if
         * we should roam from our current connection to one that
         * might be better.  This only applies when we're operating
         * in sta mode and automatic roaming is set.
         * XXX defer if busy
         * XXX repeater station
         * XXX do when !bgscan?
         */
        KASSERT(vap->iv_opmode == IEEE80211_M_STA,
                ("wrong mode %u", vap->iv_opmode));
        if (vap->iv_roaming == IEEE80211_ROAMING_AUTO &&
            (vap->iv_flags & IEEE80211_F_BGSCAN) &&
            vap->iv_state >= IEEE80211_S_RUN)
                /* XXX vap is implicit */
                sta_roam_check(ss, vap);
}

/*
 * Iterate over the entries in the scan cache, invoking
 * the callback function on each one.
 */
static void
sta_iterate(struct ieee80211_scan_state *ss, 
        ieee80211_scan_iter_func *f, void *arg)
{
        struct sta_table *st = ss->ss_priv;
        struct sta_entry *se;
        u_int gen;

        IEEE80211_SCAN_ITER_LOCK(st);
        gen = st->st_scaniter++;
restart:
        IEEE80211_SCAN_TABLE_LOCK(st);
        TAILQ_FOREACH(se, &st->st_entry, se_list) {
                if (se->se_scangen != gen) {
                        se->se_scangen = gen;
                        /* update public state */
                        se->base.se_age = ticks - se->se_lastupdate;
                        IEEE80211_SCAN_TABLE_UNLOCK(st);
                        (*f)(arg, &se->base);
                        goto restart;
                }
        }
        IEEE80211_SCAN_TABLE_UNLOCK(st);

        IEEE80211_SCAN_ITER_UNLOCK(st);
}

static void
sta_assoc_fail(struct ieee80211_scan_state *ss,
        const uint8_t macaddr[IEEE80211_ADDR_LEN], int reason)
{
        struct sta_table *st = ss->ss_priv;
        struct sta_entry *se;

        se = sta_lookup(st, macaddr);
        if (se != NULL) {
                se->se_fails++;
                se->se_lastfail = ticks;
                IEEE80211_NOTE_MAC(ss->ss_vap, IEEE80211_MSG_SCAN,
                    macaddr, "%s: reason %u fails %u",
                    __func__, reason, se->se_fails);
        }
}

static void
sta_assoc_success(struct ieee80211_scan_state *ss,
        const uint8_t macaddr[IEEE80211_ADDR_LEN])
{
        struct sta_table *st = ss->ss_priv;
        struct sta_entry *se;

        se = sta_lookup(st, macaddr);
        if (se != NULL) {
#if 0
                se->se_fails = 0;
                IEEE80211_NOTE_MAC(ss->ss_vap, IEEE80211_MSG_SCAN,
                    macaddr, "%s: fails %u",
                    __func__, se->se_fails);
#endif
                se->se_lastassoc = ticks;
        }
}

static const struct ieee80211_scanner sta_default = {
        .scan_name              = "default",
        .scan_attach            = sta_attach,
        .scan_detach            = sta_detach,
        .scan_start             = sta_start,
        .scan_restart           = sta_restart,
        .scan_cancel            = sta_cancel,
        .scan_end               = sta_pick_bss,
        .scan_flush             = sta_flush,
        .scan_add               = sta_add,
        .scan_age               = sta_age,
        .scan_iterate           = sta_iterate,
        .scan_assoc_fail        = sta_assoc_fail,
        .scan_assoc_success     = sta_assoc_success,
};
IEEE80211_SCANNER_ALG(sta, IEEE80211_M_STA, sta_default);

/*
 * Adhoc mode-specific support.
 */

static const uint16_t adhocWorld[] =            /* 36, 40, 44, 48 */
{ 5180, 5200, 5220, 5240 };
static const uint16_t adhocFcc3[] =             /* 36, 40, 44, 48 145, 149, 153, 157, 161, 165 */
{ 5180, 5200, 5220, 5240, 5725, 5745, 5765, 5785, 5805, 5825 };
static const uint16_t adhocMkk[] =              /* 34, 38, 42, 46 */
{ 5170, 5190, 5210, 5230 };
static const uint16_t adhoc11b[] =              /* 10, 11 */
{ 2457, 2462 };

static const struct scanlist adhocScanTable[] = {
        { IEEE80211_MODE_11B,           X(adhoc11b) },
        { IEEE80211_MODE_11A,           X(adhocWorld) },
        { IEEE80211_MODE_11A,           X(adhocFcc3) },
        { IEEE80211_MODE_11B,           X(adhocMkk) },
        { .list = NULL }
};
#undef X

/*
 * Start an adhoc-mode scan by populating the channel list.
 */
static int
adhoc_start(struct ieee80211_scan_state *ss, struct ieee80211vap *vap)
{
        struct sta_table *st = ss->ss_priv;

        makescanlist(ss, vap, adhocScanTable);

        if (ss->ss_mindwell == 0)
                ss->ss_mindwell = msecs_to_ticks(200);  /* 200ms */
        if (ss->ss_maxdwell == 0)
                ss->ss_maxdwell = msecs_to_ticks(200);  /* 200ms */

        st->st_scangen++;
        st->st_newscan = 1;

        return 0;
}

/*
 * Select a channel to start an adhoc network on.
 * The channel list was populated with appropriate
 * channels so select one that looks least occupied.
 */
static struct ieee80211_channel *
adhoc_pick_channel(struct ieee80211_scan_state *ss, int flags)
{
        struct sta_table *st = ss->ss_priv;
        struct sta_entry *se;
        struct ieee80211_channel *c, *bestchan;
        int i, bestrssi, maxrssi;

        bestchan = NULL;
        bestrssi = -1;

        IEEE80211_SCAN_TABLE_LOCK(st);
        for (i = 0; i < ss->ss_last; i++) {
                c = ss->ss_chans[i];
                /* never consider a channel with radar */
                if (IEEE80211_IS_CHAN_RADAR(c))
                        continue;
                /* skip channels disallowed by regulatory settings */
                if (IEEE80211_IS_CHAN_NOADHOC(c))
                        continue;
                /* check channel attributes for band compatibility */
                if (flags != 0 && (c->ic_flags & flags) != flags)
                        continue;
                maxrssi = 0;
                TAILQ_FOREACH(se, &st->st_entry, se_list) {
                        if (se->base.se_chan != c)
                                continue;
                        if (se->base.se_rssi > maxrssi)
                                maxrssi = se->base.se_rssi;
                }
                if (bestchan == NULL || maxrssi < bestrssi)
                        bestchan = c;
        }
        IEEE80211_SCAN_TABLE_UNLOCK(st);

        return bestchan;
}

/*
 * Pick an ibss network to join or find a channel
 * to use to start an ibss network.
 */
static int
adhoc_pick_bss(struct ieee80211_scan_state *ss, struct ieee80211vap *vap)
{
        struct sta_table *st = ss->ss_priv;
        struct sta_entry *selbs;
        struct ieee80211_channel *chan;
        struct ieee80211com *ic = vap->iv_ic;

        KASSERT(vap->iv_opmode == IEEE80211_M_IBSS ||
                vap->iv_opmode == IEEE80211_M_AHDEMO ||
                vap->iv_opmode == IEEE80211_M_MBSS,
                ("wrong opmode %u", vap->iv_opmode));

        if (st->st_newscan) {
                sta_update_notseen(st);
                st->st_newscan = 0;
        }
        if (ss->ss_flags & IEEE80211_SCAN_NOPICK) {
                /*
                 * Manual/background scan, don't select+join the
                 * bss, just return.  The scanning framework will
                 * handle notification that this has completed.
                 */
                ss->ss_flags &= ~IEEE80211_SCAN_NOPICK;
                return 1;
        }
        /*
         * Automatic sequencing; look for a candidate and
         * if found join the network.
         */
        /* NB: unlocked read should be ok */
        if (TAILQ_FIRST(&st->st_entry) == NULL) {
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                        "%s: no scan candidate\n", __func__);
                if (ss->ss_flags & IEEE80211_SCAN_NOJOIN)
                        return 0;
notfound:
                /* NB: never auto-start a tdma network for slot !0 */
#ifdef IEEE80211_SUPPORT_TDMA
                if (vap->iv_des_nssid &&
                    ((vap->iv_caps & IEEE80211_C_TDMA) == 0 ||
                     ieee80211_tdma_getslot(vap) == 0)) {
#else
                if (vap->iv_des_nssid) {
#endif
                        /*
                         * No existing adhoc network to join and we have
                         * an ssid; start one up.  If no channel was
                         * specified, try to select a channel.
                         */
                        if (vap->iv_des_chan == IEEE80211_CHAN_ANYC ||
                            IEEE80211_IS_CHAN_RADAR(vap->iv_des_chan)) {
                                chan = adhoc_pick_channel(ss, 0);
                        } else
                                chan = vap->iv_des_chan;
                        if (chan != NULL) {
                                /*
                                 * Create a HT capable IBSS; the per-node
                                 * probe request/response will result in
                                 * "correct" rate control capabilities being
                                 * negotiated.
                                 */
                                chan = ieee80211_ht_adjust_channel(ic,
                                    chan, vap->iv_flags_ht);
                                chan = ieee80211_vht_adjust_channel(ic,
                                    chan, vap->iv_vht_flags);
                                ieee80211_create_ibss(vap, chan);
                                return 1;
                        }
                }
                /*
                 * If nothing suitable was found decrement
                 * the failure counts so entries will be
                 * reconsidered the next time around.  We
                 * really want to do this only for sta's
                 * where we've previously had some success.
                 */
                sta_dec_fails(st);
                st->st_newscan = 1;
                return 0;                       /* restart scan */
        }
        selbs = select_bss(ss, vap, IEEE80211_MSG_SCAN);
        if (ss->ss_flags & IEEE80211_SCAN_NOJOIN)
                return (selbs != NULL);
        if (selbs == NULL)
                goto notfound;
        chan = selbs->base.se_chan;
        if (selbs->se_flags & STA_DEMOTE11B)
                chan = demote11b(vap, chan);
        /*
         * If HT is available, make it a possibility here.
         * The intent is to enable HT20/HT40 when joining a non-HT
         * IBSS node; we can then advertise HT IEs and speak HT
         * to any subsequent nodes that support it.
         */
        chan = ieee80211_ht_adjust_channel(ic,
            chan, vap->iv_flags_ht);
        chan = ieee80211_vht_adjust_channel(ic,
            chan, vap->iv_vht_flags);
        if (!ieee80211_sta_join(vap, chan, &selbs->base))
                goto notfound;
        return 1;                               /* terminate scan */
}

/*
 * Age entries in the scan cache.
 */
static void
adhoc_age(struct ieee80211_scan_state *ss)
{
        struct sta_table *st = ss->ss_priv;
        struct sta_entry *se, *next;

        IEEE80211_SCAN_TABLE_LOCK(st);
        TAILQ_FOREACH_SAFE(se, &st->st_entry, se_list, next) {
                if (se->se_notseen > STA_PURGE_SCANS) {
                        TAILQ_REMOVE(&st->st_entry, se, se_list);
                        LIST_REMOVE(se, se_hash);
                        ieee80211_ies_cleanup(&se->base.se_ies);
                        IEEE80211_FREE(se, M_80211_SCAN);
                }
        }
        IEEE80211_SCAN_TABLE_UNLOCK(st);
}

static const struct ieee80211_scanner adhoc_default = {
        .scan_name              = "default",
        .scan_attach            = sta_attach,
        .scan_detach            = sta_detach,
        .scan_start             = adhoc_start,
        .scan_restart           = sta_restart,
        .scan_cancel            = sta_cancel,
        .scan_end               = adhoc_pick_bss,
        .scan_flush             = sta_flush,
        .scan_pickchan          = adhoc_pick_channel,
        .scan_add               = sta_add,
        .scan_age               = adhoc_age,
        .scan_iterate           = sta_iterate,
        .scan_assoc_fail        = sta_assoc_fail,
        .scan_assoc_success     = sta_assoc_success,
};
IEEE80211_SCANNER_ALG(ibss, IEEE80211_M_IBSS, adhoc_default);
IEEE80211_SCANNER_ALG(ahdemo, IEEE80211_M_AHDEMO, adhoc_default);

static int
ap_start(struct ieee80211_scan_state *ss, struct ieee80211vap *vap)
{
        struct sta_table *st = ss->ss_priv;

        makescanlist(ss, vap, staScanTable);

        if (ss->ss_mindwell == 0)
                ss->ss_mindwell = msecs_to_ticks(200);  /* 200ms */
        if (ss->ss_maxdwell == 0)
                ss->ss_maxdwell = msecs_to_ticks(200);  /* 200ms */

        st->st_scangen++;
        st->st_newscan = 1;

        return 0;
}

/*
 * Cancel an ongoing scan.
 */
static int
ap_cancel(struct ieee80211_scan_state *ss, struct ieee80211vap *vap)
{
        return 0;
}

/*
 * Pick a quiet channel to use for ap operation.
 */
static struct ieee80211_channel *
ap_pick_channel(struct ieee80211_scan_state *ss, int flags)
{
        struct sta_table *st = ss->ss_priv;
        struct ieee80211_channel *bestchan = NULL;
        int i;

        /* XXX select channel more intelligently, e.g. channel spread, power */
        /* NB: use scan list order to preserve channel preference */
        for (i = 0; i < ss->ss_last; i++) {
                struct ieee80211_channel *chan = ss->ss_chans[i];
                /*
                 * If the channel is unoccupied the max rssi
                 * should be zero; just take it.  Otherwise
                 * track the channel with the lowest rssi and
                 * use that when all channels appear occupied.
                 */
                if (IEEE80211_IS_CHAN_RADAR(chan))
                        continue;
                if (IEEE80211_IS_CHAN_NOHOSTAP(chan))
                        continue;
                /* check channel attributes for band compatibility */
                if (flags != 0 && (chan->ic_flags & flags) != flags)
                        continue;
                KASSERT(sizeof(chan->ic_ieee) == 1, ("ic_chan size"));
                /* XXX channel have interference */
                if (st->st_maxrssi[chan->ic_ieee] == 0) {
                        /* XXX use other considerations */
                        return chan;
                }
                if (bestchan == NULL ||
                    st->st_maxrssi[chan->ic_ieee] < st->st_maxrssi[bestchan->ic_ieee])
                        bestchan = chan;
        }
        return bestchan;
}

/*
 * Pick a quiet channel to use for ap operation.
 */
static int
ap_end(struct ieee80211_scan_state *ss, struct ieee80211vap *vap)
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_channel *bestchan, *chan;

        KASSERT(vap->iv_opmode == IEEE80211_M_HOSTAP,
                ("wrong opmode %u", vap->iv_opmode));
        bestchan = ap_pick_channel(ss, 0);
        if (bestchan == NULL) {
                /* no suitable channel, should not happen */
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                    "%s: no suitable channel! (should not happen)\n", __func__);
                /* XXX print something? */
                return 0;                       /* restart scan */
        }
        /*
         * If this is a dynamic turbo channel, start with the unboosted one.
         */
        if (IEEE80211_IS_CHAN_TURBO(bestchan)) {
                bestchan = ieee80211_find_channel(ic, bestchan->ic_freq,
                        bestchan->ic_flags & ~IEEE80211_CHAN_TURBO);
                if (bestchan == NULL) {
                        /* should never happen ?? */
                        return 0;
                }
        }
        if (ss->ss_flags & (IEEE80211_SCAN_NOPICK | IEEE80211_SCAN_NOJOIN)) {
                /*
                 * Manual/background scan, don't select+join the
                 * bss, just return.  The scanning framework will
                 * handle notification that this has completed.
                 */
                ss->ss_flags &= ~IEEE80211_SCAN_NOPICK;
                return 1;
        }
        chan = ieee80211_ht_adjust_channel(ic, bestchan, vap->iv_flags_ht);
        chan = ieee80211_vht_adjust_channel(ic, chan, vap->iv_vht_flags);
        ieee80211_create_ibss(vap, chan);

        return 1;
}

static const struct ieee80211_scanner ap_default = {
        .scan_name              = "default",
        .scan_attach            = sta_attach,
        .scan_detach            = sta_detach,
        .scan_start             = ap_start,
        .scan_restart           = sta_restart,
        .scan_cancel            = ap_cancel,
        .scan_end               = ap_end,
        .scan_flush             = sta_flush,
        .scan_pickchan          = ap_pick_channel,
        .scan_add               = sta_add,
        .scan_age               = adhoc_age,
        .scan_iterate           = sta_iterate,
        .scan_assoc_success     = sta_assoc_success,
        .scan_assoc_fail        = sta_assoc_fail,
};
IEEE80211_SCANNER_ALG(ap, IEEE80211_M_HOSTAP, ap_default);

#ifdef IEEE80211_SUPPORT_MESH
/*
 * Pick an mbss network to join or find a channel
 * to use to start an mbss network.
 */
static int
mesh_pick_bss(struct ieee80211_scan_state *ss, struct ieee80211vap *vap)
{
        struct sta_table *st = ss->ss_priv;
        struct ieee80211_mesh_state *ms = vap->iv_mesh;
        struct sta_entry *selbs;
        struct ieee80211_channel *chan;

        KASSERT(vap->iv_opmode == IEEE80211_M_MBSS,
                ("wrong opmode %u", vap->iv_opmode));

        if (st->st_newscan) {
                sta_update_notseen(st);
                st->st_newscan = 0;
        }
        if (ss->ss_flags & IEEE80211_SCAN_NOPICK) {
                /*
                 * Manual/background scan, don't select+join the
                 * bss, just return.  The scanning framework will
                 * handle notification that this has completed.
                 */
                ss->ss_flags &= ~IEEE80211_SCAN_NOPICK;
                return 1;
        }
        /*
         * Automatic sequencing; look for a candidate and
         * if found join the network.
         */
        /* NB: unlocked read should be ok */
        if (TAILQ_FIRST(&st->st_entry) == NULL) {
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                        "%s: no scan candidate\n", __func__);
                if (ss->ss_flags & IEEE80211_SCAN_NOJOIN)
                        return 0;
notfound:
                if (ms->ms_idlen != 0) {
                        /*
                         * No existing mbss network to join and we have
                         * a meshid; start one up.  If no channel was
                         * specified, try to select a channel.
                         */
                        if (vap->iv_des_chan == IEEE80211_CHAN_ANYC ||
                            IEEE80211_IS_CHAN_RADAR(vap->iv_des_chan)) {
                                struct ieee80211com *ic = vap->iv_ic;

                                /* XXX VHT */
                                chan = adhoc_pick_channel(ss, 0);
                                if (chan != NULL) {
                                        chan = ieee80211_ht_adjust_channel(ic,
                                            chan, vap->iv_flags_ht);
                                        chan = ieee80211_vht_adjust_channel(ic,
                                            chan, vap->iv_vht_flags);
                                        }
                        } else
                                chan = vap->iv_des_chan;
                        if (chan != NULL) {
                                ieee80211_create_ibss(vap, chan);
                                return 1;
                        }
                }
                /*
                 * If nothing suitable was found decrement
                 * the failure counts so entries will be
                 * reconsidered the next time around.  We
                 * really want to do this only for sta's
                 * where we've previously had some success.
                 */
                sta_dec_fails(st);
                st->st_newscan = 1;
                return 0;                       /* restart scan */
        }
        selbs = select_bss(ss, vap, IEEE80211_MSG_SCAN);
        if (ss->ss_flags & IEEE80211_SCAN_NOJOIN)
                return (selbs != NULL);
        if (selbs == NULL)
                goto notfound;
        chan = selbs->base.se_chan;
        if (selbs->se_flags & STA_DEMOTE11B)
                chan = demote11b(vap, chan);
        if (!ieee80211_sta_join(vap, chan, &selbs->base))
                goto notfound;
        return 1;                               /* terminate scan */
}

static const struct ieee80211_scanner mesh_default = {
        .scan_name              = "default",
        .scan_attach            = sta_attach,
        .scan_detach            = sta_detach,
        .scan_start             = adhoc_start,
        .scan_restart           = sta_restart,
        .scan_cancel            = sta_cancel,
        .scan_end               = mesh_pick_bss,
        .scan_flush             = sta_flush,
        .scan_pickchan          = adhoc_pick_channel,
        .scan_add               = sta_add,
        .scan_age               = adhoc_age,
        .scan_iterate           = sta_iterate,
        .scan_assoc_fail        = sta_assoc_fail,
        .scan_assoc_success     = sta_assoc_success,
};
IEEE80211_SCANNER_ALG(mesh, IEEE80211_M_MBSS, mesh_default);
#endif /* IEEE80211_SUPPORT_MESH */