wlan - Import initial full-offload scan support from FreeBSD.

[dragonfly.git] / sys / netproto / 802_11 / wlan / ieee80211_scan_sw.c

/*-
 * Copyright (c) 2002-2008 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>
__FBSDID("$FreeBSD$");

/*
 * IEEE 802.11 scanning support.
 */
#include "opt_wlan.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/condvar.h>

#include <sys/socket.h>

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

#include <netproto/802_11/ieee80211_var.h>

#include <netproto/802_11/ieee80211_scan_sw.h>

#include <net/bpf.h>

struct scan_state {
        struct ieee80211_scan_state base;       /* public state */

        u_int                   ss_iflags;      /* flags used internally */
#define ISCAN_MINDWELL          0x0001          /* min dwell time reached */
#define ISCAN_DISCARD           0x0002          /* discard rx'd frames */
#define ISCAN_CANCEL            0x0004          /* cancel current scan */
#define ISCAN_ABORT             0x0008          /* end the scan immediately */
#define ISCAN_RUNNING           0x0010          /* scan was started */

        unsigned long           ss_chanmindwell;  /* min dwell on curchan */
        unsigned long           ss_scanend;     /* time scan must stop */
        u_int                   ss_duration;    /* duration for next scan */
        struct task             ss_scan_start;  /* scan start */
        struct timeout_task     ss_scan_curchan;  /* scan execution */
};
#define SCAN_PRIVATE(ss)        ((struct scan_state *) ss)

/*
 * Amount of time to go off-channel during a background
 * scan.  This value should be large enough to catch most
 * ap's but short enough that we can return on-channel
 * before our listen interval expires.
 *
 * XXX tunable
 * XXX check against configured listen interval
 */
#define IEEE80211_SCAN_OFFCHANNEL       msecs_to_ticks(150)

/*
 * Roaming-related defaults.  RSSI thresholds are as returned by the
 * driver (.5dBm).  Transmit rate thresholds are IEEE rate codes (i.e
 * .5M units) or MCS.
 */
/* rssi thresholds */
#define ROAM_RSSI_11A_DEFAULT           14      /* 11a bss */
#define ROAM_RSSI_11B_DEFAULT           14      /* 11b bss */
#define ROAM_RSSI_11BONLY_DEFAULT       14      /* 11b-only bss */
/* transmit rate thresholds */
#define ROAM_RATE_11A_DEFAULT           2*12    /* 11a bss */
#define ROAM_RATE_11B_DEFAULT           2*5     /* 11b bss */
#define ROAM_RATE_11BONLY_DEFAULT       2*1     /* 11b-only bss */
#define ROAM_RATE_HALF_DEFAULT          2*6     /* half-width 11a/g bss */
#define ROAM_RATE_QUARTER_DEFAULT       2*3     /* quarter-width 11a/g bss */
#define ROAM_MCS_11N_DEFAULT            (1 | IEEE80211_RATE_MCS) /* 11n bss */

static  void scan_curchan(struct ieee80211_scan_state *, unsigned long);
static  void scan_mindwell(struct ieee80211_scan_state *);
static  void scan_signal(struct ieee80211_scan_state *, int);
static  void scan_signal_locked(struct ieee80211_scan_state *, int);
static  void scan_start(void *, int);
static  void scan_curchan_task(void *, int);
static  void scan_end(struct ieee80211_scan_state *, int);
static  void scan_done(struct ieee80211_scan_state *, int);

MALLOC_DEFINE(M_80211_SCAN, "80211scan", "802.11 scan state");

static void
ieee80211_swscan_detach(struct ieee80211com *ic)
{
        struct ieee80211_scan_state *ss = ic->ic_scan;

        if (ss != NULL) {
                scan_signal(ss, ISCAN_ABORT);
                ieee80211_draintask(ic, &SCAN_PRIVATE(ss)->ss_scan_start);
                taskqueue_drain_timeout(ic->ic_tq,
                    &SCAN_PRIVATE(ss)->ss_scan_curchan);
                KASSERT((ic->ic_flags & IEEE80211_F_SCAN) == 0,
                    ("scan still running"));

                /*
                 * For now, do the ss_ops detach here rather
                 * than ieee80211_scan_detach().
                 *
                 * I'll figure out how to cleanly split things up
                 * at a later date.
                 */
                if (ss->ss_ops != NULL) {
                        ss->ss_ops->scan_detach(ss);
                        ss->ss_ops = NULL;
                }
                ic->ic_scan = NULL;
                IEEE80211_FREE(SCAN_PRIVATE(ss), M_80211_SCAN);
        }
}

static void
ieee80211_swscan_vattach(struct ieee80211vap *vap)
{
        /* nothing to do for now */
        /*
         * TODO: all of the vap scan calls should be methods!
         */

}

static void
ieee80211_swscan_vdetach(struct ieee80211vap *vap)
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_scan_state *ss = ic->ic_scan;

        IEEE80211_LOCK_ASSERT(ic);

        if (ss != NULL && ss->ss_vap == vap &&
            (ic->ic_flags & IEEE80211_F_SCAN))
                scan_signal_locked(ss, ISCAN_ABORT);
}

static void
ieee80211_swscan_set_scan_duration(struct ieee80211vap *vap, u_int duration)
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_scan_state *ss = ic->ic_scan;

        IEEE80211_LOCK_ASSERT(ic);

        /* NB: flush frames rx'd before 1st channel change */
        SCAN_PRIVATE(ss)->ss_iflags |= ISCAN_DISCARD;
        SCAN_PRIVATE(ss)->ss_duration = duration;
}

/*
 * Start a scan unless one is already going.
 */
static int
ieee80211_swscan_start_scan_locked(const struct ieee80211_scanner *scan,
    struct ieee80211vap *vap, int flags, u_int duration,
    u_int mindwell, u_int maxdwell,
    u_int nssid, const struct ieee80211_scan_ssid ssids[])
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_scan_state *ss = ic->ic_scan;

        IEEE80211_LOCK_ASSERT(ic);

        if (ic->ic_flags & IEEE80211_F_CSAPENDING) {
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                    "%s: scan inhibited by pending channel change\n", __func__);
        } else if ((ic->ic_flags & IEEE80211_F_SCAN) == 0) {
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                    "%s: %s scan, duration %u mindwell %u maxdwell %u, desired mode %s, %s%s%s%s%s%s\n"
                    , __func__
                    , flags & IEEE80211_SCAN_ACTIVE ? "active" : "passive"
                    , duration, mindwell, maxdwell
                    , ieee80211_phymode_name[vap->iv_des_mode]
                    , flags & IEEE80211_SCAN_FLUSH ? "flush" : "append"
                    , flags & IEEE80211_SCAN_NOPICK ? ", nopick" : ""
                    , flags & IEEE80211_SCAN_NOJOIN ? ", nojoin" : ""
                    , flags & IEEE80211_SCAN_NOBCAST ? ", nobcast" : ""
                    , flags & IEEE80211_SCAN_PICK1ST ? ", pick1st" : ""
                    , flags & IEEE80211_SCAN_ONCE ? ", once" : ""
                );

                ieee80211_scan_update_locked(vap, scan);
                if (ss->ss_ops != NULL) {
                        if ((flags & IEEE80211_SCAN_NOSSID) == 0)
                                ieee80211_scan_copy_ssid(vap, ss, nssid, ssids);

                        /* NB: top 4 bits for internal use */
                        ss->ss_flags = flags & 0xfff;
                        if (ss->ss_flags & IEEE80211_SCAN_ACTIVE)
                                vap->iv_stats.is_scan_active++;
                        else
                                vap->iv_stats.is_scan_passive++;
                        if (flags & IEEE80211_SCAN_FLUSH)
                                ss->ss_ops->scan_flush(ss);
                        if (flags & IEEE80211_SCAN_BGSCAN)
                                ic->ic_flags_ext |= IEEE80211_FEXT_BGSCAN;

                        /* Set duration for this particular scan */
                        ieee80211_swscan_set_scan_duration(vap, duration);

                        ss->ss_next = 0;
                        ss->ss_mindwell = mindwell;
                        ss->ss_maxdwell = maxdwell;
                        /* NB: scan_start must be before the scan runtask */
                        ss->ss_ops->scan_start(ss, vap);
#ifdef IEEE80211_DEBUG
                        if (ieee80211_msg_scan(vap))
                                ieee80211_scan_dump(ss);
#endif /* IEEE80211_DEBUG */
                        ic->ic_flags |= IEEE80211_F_SCAN;

                        /* Start scan task */
                        ieee80211_runtask(ic, &SCAN_PRIVATE(ss)->ss_scan_start);
                }
                return 1;
        } else {
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                    "%s: %s scan already in progress\n", __func__,
                    ss->ss_flags & IEEE80211_SCAN_ACTIVE ? "active" : "passive");
        }
        return 0;
}


/*
 * Start a scan unless one is already going.
 *
 * Called without the comlock held; grab the comlock as appropriate.
 */
static int
ieee80211_swscan_start_scan(const struct ieee80211_scanner *scan,
    struct ieee80211vap *vap, int flags,
    u_int duration, u_int mindwell, u_int maxdwell,
    u_int nssid, const struct ieee80211_scan_ssid ssids[])
{
        struct ieee80211com *ic = vap->iv_ic;
        int result;

        IEEE80211_UNLOCK_ASSERT(ic);

        IEEE80211_LOCK(ic);
        result = ieee80211_swscan_start_scan_locked(scan, vap, flags, duration,
            mindwell, maxdwell, nssid, ssids);
        IEEE80211_UNLOCK(ic);

        return result;
}

/*
 * Check the scan cache for an ap/channel to use; if that
 * fails then kick off a new scan.
 *
 * Called with the comlock held.
 *
 * XXX TODO: split out!
 */
static int
ieee80211_swscan_check_scan(const struct ieee80211_scanner *scan,
    struct ieee80211vap *vap, int flags,
    u_int duration, u_int mindwell, u_int maxdwell,
    u_int nssid, const struct ieee80211_scan_ssid ssids[])
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_scan_state *ss = ic->ic_scan;
        int result;

        IEEE80211_LOCK_ASSERT(ic);

        if (ss->ss_ops != NULL) {
                /* XXX verify ss_ops matches vap->iv_opmode */
                if ((flags & IEEE80211_SCAN_NOSSID) == 0) {
                        /*
                         * Update the ssid list and mark flags so if
                         * we call start_scan it doesn't duplicate work.
                         */
                        ieee80211_scan_copy_ssid(vap, ss, nssid, ssids);
                        flags |= IEEE80211_SCAN_NOSSID;
                }
                if ((ic->ic_flags & IEEE80211_F_SCAN) == 0 &&
                    (flags & IEEE80211_SCAN_FLUSH) == 0 &&
                    ieee80211_time_before(ticks, ic->ic_lastscan + vap->iv_scanvalid)) {
                        /*
                         * We're not currently scanning and the cache is
                         * deemed hot enough to consult.  Lock out others
                         * by marking IEEE80211_F_SCAN while we decide if
                         * something is already in the scan cache we can
                         * use.  Also discard any frames that might come
                         * in while temporarily marked as scanning.
                         */
                        SCAN_PRIVATE(ss)->ss_iflags |= ISCAN_DISCARD;
                        ic->ic_flags |= IEEE80211_F_SCAN;

                        /* NB: need to use supplied flags in check */
                        ss->ss_flags = flags & 0xff;
                        result = ss->ss_ops->scan_end(ss, vap);

                        ic->ic_flags &= ~IEEE80211_F_SCAN;
                        SCAN_PRIVATE(ss)->ss_iflags &= ~ISCAN_DISCARD;
                        if (result) {
                                ieee80211_notify_scan_done(vap);
                                return 1;
                        }
                }
        }
        result = ieee80211_swscan_start_scan_locked(scan, vap, flags, duration,
            mindwell, maxdwell, nssid, ssids);

        return result;
}

/*
 * Restart a previous scan.  If the previous scan completed
 * then we start again using the existing channel list.
 */
static int
ieee80211_swscan_bg_scan(const struct ieee80211_scanner *scan,
    struct ieee80211vap *vap, int flags)
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_scan_state *ss = ic->ic_scan;

        /* XXX assert unlocked? */
        // IEEE80211_UNLOCK_ASSERT(ic);

        IEEE80211_LOCK(ic);
        if ((ic->ic_flags & IEEE80211_F_SCAN) == 0) {
                u_int duration;
                /*
                 * Go off-channel for a fixed interval that is large
                 * enough to catch most ap's but short enough that
                 * we can return on-channel before our listen interval
                 * expires.
                 */
                duration = IEEE80211_SCAN_OFFCHANNEL;

                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                    "%s: %s scan, ticks %u duration %u\n", __func__,
                    ss->ss_flags & IEEE80211_SCAN_ACTIVE ? "active" : "passive",
                    ticks, duration);

                ieee80211_scan_update_locked(vap, scan);
                if (ss->ss_ops != NULL) {
                        ss->ss_vap = vap;
                        /*
                         * A background scan does not select a new sta; it
                         * just refreshes the scan cache.  Also, indicate
                         * the scan logic should follow the beacon schedule:
                         * we go off-channel and scan for a while, then
                         * return to the bss channel to receive a beacon,
                         * then go off-channel again.  All during this time
                         * we notify the ap we're in power save mode.  When
                         * the scan is complete we leave power save mode.
                         * If any beacon indicates there are frames pending
                         * for us then we drop out of power save mode
                         * (and background scan) automatically by way of the
                         * usual sta power save logic.
                         */
                        ss->ss_flags |= IEEE80211_SCAN_NOPICK
                                     |  IEEE80211_SCAN_BGSCAN
                                     |  flags
                                     ;
                        /* if previous scan completed, restart */
                        if (ss->ss_next >= ss->ss_last) {
                                if (ss->ss_flags & IEEE80211_SCAN_ACTIVE)
                                        vap->iv_stats.is_scan_active++;
                                else
                                        vap->iv_stats.is_scan_passive++;
                                /*
                                 * NB: beware of the scan cache being flushed;
                                 *     if the channel list is empty use the
                                 *     scan_start method to populate it.
                                 */
                                ss->ss_next = 0;
                                if (ss->ss_last != 0)
                                        ss->ss_ops->scan_restart(ss, vap);
                                else {
                                        ss->ss_ops->scan_start(ss, vap);
#ifdef IEEE80211_DEBUG
                                        if (ieee80211_msg_scan(vap))
                                                ieee80211_scan_dump(ss);
#endif /* IEEE80211_DEBUG */
                                }
                        }
                        ieee80211_swscan_set_scan_duration(vap, duration);
                        ss->ss_maxdwell = duration;
                        ic->ic_flags |= IEEE80211_F_SCAN;
                        ic->ic_flags_ext |= IEEE80211_FEXT_BGSCAN;
                        ieee80211_runtask(ic,
                            &SCAN_PRIVATE(ss)->ss_scan_start);
                } else {
                        /* XXX msg+stat */
                }
        } else {
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                    "%s: %s scan already in progress\n", __func__,
                    ss->ss_flags & IEEE80211_SCAN_ACTIVE ? "active" : "passive");
        }
        IEEE80211_UNLOCK(ic);

        /* NB: racey, does it matter? */
        return (ic->ic_flags & IEEE80211_F_SCAN);
}

/*
 * Taskqueue work to cancel a scan.
 *
 * Note: for offload scan devices, we may want to call into the
 * driver to try and cancel scanning, however it may not be cancelable.
 */
static void
cancel_scan(struct ieee80211vap *vap, int any, const char *func)
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_scan_state *ss = ic->ic_scan;

        IEEE80211_LOCK(ic);
        if ((ic->ic_flags & IEEE80211_F_SCAN) &&
            (any || ss->ss_vap == vap) &&
            (SCAN_PRIVATE(ss)->ss_iflags & ISCAN_CANCEL) == 0) {
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                    "%s: cancel %s scan\n", func,
                    ss->ss_flags & IEEE80211_SCAN_ACTIVE ?
                        "active" : "passive");

                /* clear bg scan NOPICK */
                ss->ss_flags &= ~IEEE80211_SCAN_NOPICK;
                /* mark cancel request and wake up the scan task */
                scan_signal_locked(ss, ISCAN_CANCEL);
        } else {
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                    "%s: called; F_SCAN=%d, vap=%s, CANCEL=%d\n",
                        func,
                        !! (ic->ic_flags & IEEE80211_F_SCAN),
                        (ss->ss_vap == vap ? "match" : "nomatch"),
                        !! (SCAN_PRIVATE(ss)->ss_iflags & ISCAN_CANCEL));
        }
        IEEE80211_UNLOCK(ic);
}

/*
 * Cancel any scan currently going on for the specified vap.
 */
static void
ieee80211_swscan_cancel_scan(struct ieee80211vap *vap)
{
        cancel_scan(vap, 0, __func__);
}

/*
 * Cancel any scan currently going on.
 */
static void
ieee80211_swscan_cancel_anyscan(struct ieee80211vap *vap)
{
        /* XXX for now - just don't do this per packet. */
        if (vap->iv_flags_ext & IEEE80211_FEXT_SCAN_OFFLOAD)
                return;

        cancel_scan(vap, 1, __func__);
}

/*
 * Manually switch to the next channel in the channel list.
 * Provided for drivers that manage scanning themselves
 * (e.g. for firmware-based devices).
 */
static void
ieee80211_swscan_scan_next(struct ieee80211vap *vap)
{
        struct ieee80211_scan_state *ss = vap->iv_ic->ic_scan;

        IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN, "%s: called\n", __func__);

        /* wake up the scan task */
        scan_signal(ss, 0);
}

/*
 * Manually stop a scan that is currently running.
 * Provided for drivers that are not able to scan single channels
 * (e.g. for firmware-based devices).
 */
static void
ieee80211_swscan_scan_done(struct ieee80211vap *vap)
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_scan_state *ss = ic->ic_scan;

        IEEE80211_LOCK_ASSERT(ic);

        scan_signal_locked(ss, 0);
}

/*
 * Probe the current channel, if allowed, while scanning.
 * If the channel is not marked passive-only then send
 * a probe request immediately.  Otherwise mark state and
 * listen for beacons on the channel; if we receive something
 * then we'll transmit a probe request.
 */
static void
ieee80211_swscan_probe_curchan(struct ieee80211vap *vap, int force)
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_scan_state *ss = ic->ic_scan;
        struct ifnet *ifp = vap->iv_ifp;
        int i;

        /*
         * Full-offload scan devices don't require this.
         */
        if (vap->iv_flags_ext & IEEE80211_FEXT_SCAN_OFFLOAD)
                return;

        /*
         * Send directed probe requests followed by any
         * broadcast probe request.
         * XXX remove dependence on ic/vap->iv_bss
         */
        for (i = 0; i < ss->ss_nssid; i++)
                ieee80211_send_probereq(vap->iv_bss,
                        vap->iv_myaddr, ifp->if_broadcastaddr,
                        ifp->if_broadcastaddr,
                        ss->ss_ssid[i].ssid, ss->ss_ssid[i].len);
        if ((ss->ss_flags & IEEE80211_SCAN_NOBCAST) == 0)
                ieee80211_send_probereq(vap->iv_bss,
                        vap->iv_myaddr, ifp->if_broadcastaddr,
                        ifp->if_broadcastaddr,
                        "", 0);
}

/*
 * Scan curchan.  If this is an active scan and the channel
 * is not marked passive then send probe request frame(s).
 * Arrange for the channel change after maxdwell ticks.
 */
static void
scan_curchan(struct ieee80211_scan_state *ss, unsigned long maxdwell)
{
        struct ieee80211vap *vap  = ss->ss_vap;
        struct ieee80211com *ic = ss->ss_ic;

        IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
            "%s: calling; maxdwell=%lu\n",
            __func__,
            maxdwell);
        IEEE80211_LOCK(ic);
        if (ss->ss_flags & IEEE80211_SCAN_ACTIVE)
                ieee80211_probe_curchan(vap, 0);
        taskqueue_enqueue_timeout(ic->ic_tq,
            &SCAN_PRIVATE(ss)->ss_scan_curchan, maxdwell);
        IEEE80211_UNLOCK(ic);
}

static void
scan_signal(struct ieee80211_scan_state *ss, int iflags)
{
        struct ieee80211com *ic = ss->ss_ic;

        IEEE80211_UNLOCK_ASSERT(ic);

        IEEE80211_LOCK(ic);
        scan_signal_locked(ss, iflags);
        IEEE80211_UNLOCK(ic);
}

static void
scan_signal_locked(struct ieee80211_scan_state *ss, int iflags)
{
        struct scan_state *ss_priv = SCAN_PRIVATE(ss);
        struct timeout_task *scan_task = &ss_priv->ss_scan_curchan;
        struct ieee80211com *ic = ss->ss_ic;

        IEEE80211_LOCK_ASSERT(ic);

        ss_priv->ss_iflags |= iflags;
        if (ss_priv->ss_iflags & ISCAN_RUNNING) {
                if (taskqueue_cancel_timeout(ic->ic_tq, scan_task, NULL) == 0)
                        taskqueue_enqueue_timeout(ic->ic_tq, scan_task, 0);
        }
}

/*
 * Handle mindwell requirements completed; initiate a channel
 * change to the next channel asap.
 */
static void
scan_mindwell(struct ieee80211_scan_state *ss)
{

        IEEE80211_DPRINTF(ss->ss_vap, IEEE80211_MSG_SCAN, "%s: called\n",
            __func__);

        scan_signal(ss, 0);
}

static void
scan_start(void *arg, int pending)
{
#define ISCAN_REP       (ISCAN_MINDWELL | ISCAN_DISCARD)
        struct ieee80211_scan_state *ss = (struct ieee80211_scan_state *) arg;
        struct scan_state *ss_priv = SCAN_PRIVATE(ss);
        struct ieee80211vap *vap = ss->ss_vap;
        struct ieee80211com *ic = ss->ss_ic;

        IEEE80211_LOCK(ic);
        if (vap == NULL || (ic->ic_flags & IEEE80211_F_SCAN) == 0 ||
            (ss_priv->ss_iflags & ISCAN_ABORT)) {
                /* Cancelled before we started */
                scan_done(ss, 0);
                return;
        }

        if (ss->ss_next == ss->ss_last) {
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                        "%s: no channels to scan\n", __func__);
                scan_done(ss, 1);
                return;
        }

        /*
         * Put the station into power save mode.
         *
         * This is only required if we're not a full-offload device;
         * those devices manage scan/traffic differently.
         */
        if (((vap->iv_flags_ext & IEEE80211_FEXT_SCAN_OFFLOAD) == 0) &&
            vap->iv_opmode == IEEE80211_M_STA &&
            vap->iv_state == IEEE80211_S_RUN) {
                if ((vap->iv_bss->ni_flags & IEEE80211_NODE_PWR_MGT) == 0) {
                        /* Enable station power save mode */
                        vap->iv_sta_ps(vap, 1);
                        /* Wait until null data frame will be ACK'ed */
#if defined(__DragonFly__)
                        lksleep(vap, IEEE80211_LOCK_OBJ(ic), PCATCH,
                            "sta_ps", msecs_to_ticks(10));
#else
                        mtx_sleep(vap, IEEE80211_LOCK_OBJ(ic), PCATCH,
                            "sta_ps", msecs_to_ticks(10));
#endif
                        if (ss_priv->ss_iflags & ISCAN_ABORT) {
                                scan_done(ss, 0);
                                return;
                        }
                }
        }

        ss_priv->ss_scanend = ticks + ss_priv->ss_duration;

        /* XXX scan state can change! Re-validate scan state! */

        IEEE80211_UNLOCK(ic);

        ic->ic_scan_start(ic);          /* notify driver */

        scan_curchan_task(ss, 0);
}

static void
scan_curchan_task(void *arg, int pending)
{
        struct ieee80211_scan_state *ss = arg;
        struct scan_state *ss_priv = SCAN_PRIVATE(ss);
        struct ieee80211com *ic = ss->ss_ic;
        struct ieee80211_channel *chan;
        unsigned long maxdwell;
        int scandone;

        IEEE80211_LOCK(ic);
end:
        scandone = (ss->ss_next >= ss->ss_last) ||
            (ss_priv->ss_iflags & ISCAN_CANCEL) != 0;

        IEEE80211_DPRINTF(ss->ss_vap, IEEE80211_MSG_SCAN,
            "%s: loop start; scandone=%d\n",
            __func__,
            scandone);

        if (scandone || (ss->ss_flags & IEEE80211_SCAN_GOTPICK) ||
            (ss_priv->ss_iflags & ISCAN_ABORT) ||
             ieee80211_time_after(ticks + ss->ss_mindwell, ss_priv->ss_scanend)) {
                ss_priv->ss_iflags &= ~ISCAN_RUNNING;
                scan_end(ss, scandone);
                return;
        } else
                ss_priv->ss_iflags |= ISCAN_RUNNING;

        chan = ss->ss_chans[ss->ss_next++];

        /*
         * Watch for truncation due to the scan end time.
         */
        if (ieee80211_time_after(ticks + ss->ss_maxdwell, ss_priv->ss_scanend))
                maxdwell = ss_priv->ss_scanend - ticks;
        else
                maxdwell = ss->ss_maxdwell;

        IEEE80211_DPRINTF(ss->ss_vap, IEEE80211_MSG_SCAN,
            "%s: chan %3d%c -> %3d%c [%s, dwell min %lums max %lums]\n",
            __func__,
            ieee80211_chan2ieee(ic, ic->ic_curchan),
            ieee80211_channel_type_char(ic->ic_curchan),
            ieee80211_chan2ieee(ic, chan),
            ieee80211_channel_type_char(chan),
            (ss->ss_flags & IEEE80211_SCAN_ACTIVE) &&
                (chan->ic_flags & IEEE80211_CHAN_PASSIVE) == 0 ?
                "active" : "passive",
            ticks_to_msecs(ss->ss_mindwell), ticks_to_msecs(maxdwell));

        /*
         * Potentially change channel and phy mode.
         */
        ic->ic_curchan = chan;
        ic->ic_rt = ieee80211_get_ratetable(chan);
        IEEE80211_UNLOCK(ic);
        /*
         * Perform the channel change and scan unlocked so the driver
         * may sleep. Once set_channel returns the hardware has
         * completed the channel change.
         */
        ic->ic_set_channel(ic);
        ieee80211_radiotap_chan_change(ic);

        /*
         * Scan curchan.  Drivers for "intelligent hardware"
         * override ic_scan_curchan to tell the device to do
         * the work.  Otherwise we manage the work ourselves;
         * sending a probe request (as needed), and arming the
         * timeout to switch channels after maxdwell ticks.
         *
         * scan_curchan should only pause for the time required to
         * prepare/initiate the hardware for the scan (if at all).
         */
        ic->ic_scan_curchan(ss, maxdwell);
        IEEE80211_LOCK(ic);

        /* XXX scan state can change! Re-validate scan state! */

        ss_priv->ss_chanmindwell = ticks + ss->ss_mindwell;
        /* clear mindwell lock and initial channel change flush */
        ss_priv->ss_iflags &= ~ISCAN_REP;

        if (ss_priv->ss_iflags & (ISCAN_CANCEL|ISCAN_ABORT)) {
                taskqueue_cancel_timeout(ic->ic_tq, &ss_priv->ss_scan_curchan,
                    NULL);
                goto end;
        }

        IEEE80211_DPRINTF(ss->ss_vap, IEEE80211_MSG_SCAN, "%s: waiting\n",
            __func__);
        IEEE80211_UNLOCK(ic);
}

static void
scan_end(struct ieee80211_scan_state *ss, int scandone)
{
        struct scan_state *ss_priv = SCAN_PRIVATE(ss);
        struct ieee80211vap *vap = ss->ss_vap;
        struct ieee80211com *ic = ss->ss_ic;

        IEEE80211_LOCK_ASSERT(ic);

        IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN, "%s: out\n", __func__);

        if (ss_priv->ss_iflags & ISCAN_ABORT) {
                scan_done(ss, scandone);
                return;
        }

        IEEE80211_UNLOCK(ic);
        ic->ic_scan_end(ic);            /* notify driver */
        IEEE80211_LOCK(ic);
        /* XXX scan state can change! Re-validate scan state! */

        /*
         * Since a cancellation may have occurred during one of the
         * driver calls (whilst unlocked), update scandone.
         */
        if (scandone == 0 && (ss_priv->ss_iflags & ISCAN_CANCEL) != 0) {
                /* XXX printf? */
                if_printf(vap->iv_ifp,
                    "%s: OOPS! scan cancelled during driver call (1)!\n",
                    __func__);
                scandone = 1;
        }

        /*
         * Record scan complete time.  Note that we also do
         * this when canceled so any background scan will
         * not be restarted for a while.
         */
        if (scandone)
                ic->ic_lastscan = ticks;
        /* return to the bss channel */
        if (ic->ic_bsschan != IEEE80211_CHAN_ANYC &&
            ic->ic_curchan != ic->ic_bsschan) {
                ieee80211_setupcurchan(ic, ic->ic_bsschan);
                IEEE80211_UNLOCK(ic);
                ic->ic_set_channel(ic);
                ieee80211_radiotap_chan_change(ic);
                IEEE80211_LOCK(ic);
        }
        /* clear internal flags and any indication of a pick */
        ss_priv->ss_iflags &= ~ISCAN_REP;
        ss->ss_flags &= ~IEEE80211_SCAN_GOTPICK;

        /*
         * If not canceled and scan completed, do post-processing.
         * If the callback function returns 0, then it wants to
         * continue/restart scanning.  Unfortunately we needed to
         * notify the driver to end the scan above to avoid having
         * rx frames alter the scan candidate list.
         */
        if ((ss_priv->ss_iflags & ISCAN_CANCEL) == 0 &&
            !ss->ss_ops->scan_end(ss, vap) &&
            (ss->ss_flags & IEEE80211_SCAN_ONCE) == 0 &&
            ieee80211_time_before(ticks + ss->ss_mindwell, ss_priv->ss_scanend)) {
                IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                    "%s: done, restart "
                    "[ticks %u, dwell min %lu scanend %lu]\n",
                    __func__,
                    ticks, ss->ss_mindwell, ss_priv->ss_scanend);
                ss->ss_next = 0;        /* reset to beginning */
                if (ss->ss_flags & IEEE80211_SCAN_ACTIVE)
                        vap->iv_stats.is_scan_active++;
                else
                        vap->iv_stats.is_scan_passive++;

                ss->ss_ops->scan_restart(ss, vap);      /* XXX? */
                ieee80211_runtask(ic, &ss_priv->ss_scan_start);
                IEEE80211_UNLOCK(ic);
                return;
        }

        /* past here, scandone is ``true'' if not in bg mode */
        if ((ss->ss_flags & IEEE80211_SCAN_BGSCAN) == 0)
                scandone = 1;

        IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
            "%s: %s, [ticks %u, dwell min %lu scanend %lu]\n",
            __func__, scandone ? "done" : "stopped",
            ticks, ss->ss_mindwell, ss_priv->ss_scanend);

        /*
         * Since a cancellation may have occurred during one of the
         * driver calls (whilst unlocked), update scandone.
         */
        if (scandone == 0 && (ss_priv->ss_iflags & ISCAN_CANCEL) != 0) {
                /* XXX printf? */
                if_printf(vap->iv_ifp,
                    "%s: OOPS! scan cancelled during driver call (2)!\n",
                    __func__);
                scandone = 1;
        }

        scan_done(ss, scandone);
}

static void
scan_done(struct ieee80211_scan_state *ss, int scandone)
{
        struct scan_state *ss_priv = SCAN_PRIVATE(ss);
        struct ieee80211com *ic = ss->ss_ic;
        struct ieee80211vap *vap = ss->ss_vap;

        IEEE80211_LOCK_ASSERT(ic);

        /*
         * Clear the SCAN bit first in case frames are
         * pending on the station power save queue.  If
         * we defer this then the dispatch of the frames
         * may generate a request to cancel scanning.
         */
        ic->ic_flags &= ~IEEE80211_F_SCAN;

        /*
         * Drop out of power save mode when a scan has
         * completed.  If this scan was prematurely terminated
         * because it is a background scan then don't notify
         * the ap; we'll either return to scanning after we
         * receive the beacon frame or we'll drop out of power
         * save mode because the beacon indicates we have frames
         * waiting for us.
         */
        if (scandone) {
                /*
                 * If we're not a scan offload device, come back out of
                 * station powersave.  Offload devices handle this themselves.
                 */
                if ((vap->iv_flags_ext & IEEE80211_FEXT_SCAN_OFFLOAD) == 0)
                        vap->iv_sta_ps(vap, 0);
                if (ss->ss_next >= ss->ss_last)
                        ic->ic_flags_ext &= ~IEEE80211_FEXT_BGSCAN;
                ieee80211_notify_scan_done(vap);
        }
        ss_priv->ss_iflags &= ~(ISCAN_CANCEL|ISCAN_ABORT);
        ss_priv->ss_scanend = 0;
        ss->ss_flags &= ~(IEEE80211_SCAN_ONCE | IEEE80211_SCAN_PICK1ST);
        IEEE80211_UNLOCK(ic);
#undef ISCAN_REP
}

/*
 * Process a beacon or probe response frame.
 */
static void
ieee80211_swscan_add_scan(struct ieee80211vap *vap,
        struct ieee80211_channel *curchan,
        const struct ieee80211_scanparams *sp,
        const struct ieee80211_frame *wh,
        int subtype, int rssi, int noise)
{
        struct ieee80211com *ic = vap->iv_ic;
        struct ieee80211_scan_state *ss = ic->ic_scan;

        /* XXX locking */
        /*
         * Frames received during startup are discarded to avoid
         * using scan state setup on the initial entry to the timer
         * callback.  This can occur because the device may enable
         * rx prior to our doing the initial channel change in the
         * timer routine.
         */
        if (SCAN_PRIVATE(ss)->ss_iflags & ISCAN_DISCARD)
                return;
#ifdef IEEE80211_DEBUG
        if (ieee80211_msg_scan(vap) && (ic->ic_flags & IEEE80211_F_SCAN))
                ieee80211_scan_dump_probe_beacon(subtype, 1, wh->i_addr2, sp, rssi);
#endif
        if (ss->ss_ops != NULL &&
            ss->ss_ops->scan_add(ss, curchan, sp, wh, subtype, rssi, noise)) {
                /*
                 * If we've reached the min dwell time terminate
                 * the timer so we'll switch to the next channel.
                 */
                if ((SCAN_PRIVATE(ss)->ss_iflags & ISCAN_MINDWELL) == 0 &&
                    ieee80211_time_after_eq(ticks, SCAN_PRIVATE(ss)->ss_chanmindwell)) {
                        IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
                            "%s: chan %3d%c min dwell met (%u > %lu)\n",
                            __func__,
                            ieee80211_chan2ieee(ic, ic->ic_curchan),
                            ieee80211_channel_type_char(ic->ic_curchan),
                            ticks, SCAN_PRIVATE(ss)->ss_chanmindwell);
                        SCAN_PRIVATE(ss)->ss_iflags |= ISCAN_MINDWELL;
                        /*
                         * NB: trigger at next clock tick or wait for the
                         * hardware.
                         */
                        ic->ic_scan_mindwell(ss);
                }
        }
}

static struct ieee80211_scan_methods swscan_methods = {
        .sc_attach = ieee80211_swscan_attach,
        .sc_detach = ieee80211_swscan_detach,
        .sc_vattach = ieee80211_swscan_vattach,
        .sc_vdetach = ieee80211_swscan_vdetach,
        .sc_set_scan_duration = ieee80211_swscan_set_scan_duration,
        .sc_start_scan = ieee80211_swscan_start_scan,
        .sc_check_scan = ieee80211_swscan_check_scan,
        .sc_bg_scan = ieee80211_swscan_bg_scan,
        .sc_cancel_scan = ieee80211_swscan_cancel_scan,
        .sc_cancel_anyscan = ieee80211_swscan_cancel_anyscan,
        .sc_scan_next = ieee80211_swscan_scan_next,
        .sc_scan_done = ieee80211_swscan_scan_done,
        .sc_scan_probe_curchan = ieee80211_swscan_probe_curchan,
        .sc_add_scan = ieee80211_swscan_add_scan
};

/*
 * Default scan attach method.
 */
void
ieee80211_swscan_attach(struct ieee80211com *ic)
{
        struct scan_state *ss;

        /*
         * Setup the default methods
         */
        ic->ic_scan_methods = &swscan_methods;

        /* Allocate initial scan state */
#if defined(__DragonFly__)
        ss = (struct scan_state *) kmalloc(sizeof(struct scan_state),
                M_80211_SCAN, M_INTWAIT | M_ZERO);
#else
        ss = (struct scan_state *) IEEE80211_MALLOC(sizeof(struct scan_state),
                M_80211_SCAN, IEEE80211_M_NOWAIT | IEEE80211_M_ZERO);
#endif
        if (ss == NULL) {
                ic->ic_scan = NULL;
                return;
        }
        TASK_INIT(&ss->ss_scan_start, 0, scan_start, ss);
        TIMEOUT_TASK_INIT(ic->ic_tq, &ss->ss_scan_curchan, 0,
            scan_curchan_task, ss);

        ic->ic_scan = &ss->base;
        ss->base.ss_ic = ic;

        ic->ic_scan_curchan = scan_curchan;
        ic->ic_scan_mindwell = scan_mindwell;
}