ieee80211_scan.c

Linux下wifi实现

/*-
 * Copyright (c) 2002-2005 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.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * Alternatively, this software may be distributed under the terms of the
 * GNU General Public License ("GPL") version 2 as published by the Free
 * Software Foundation.
 *
 * 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.
 *
 * $Id: ieee80211_scan.c 1520 2006-04-21 16:57:59Z dyqith $
 */
#ifndef EXPORT_SYMTAB
#define	EXPORT_SYMTAB
#endif

/*
 * IEEE 802.11 scanning support.
 */
#include <linux/config.h>
#include <linux/version.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/random.h>
#include <linux/interrupt.h>
#include <linux/delay.h>

#include "if_media.h"

#include <net80211/ieee80211_var.h>
#include <net80211/if_athproto.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_START	0x0008		/* 1st time through next_scan */
	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 tasklet_struct ss_pwrsav;	/* sta ps ena tasklet */
	struct timer_list ss_scan_timer;	/* scan timer */
};
#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_jiffies(150)

/*
 * Roaming-related defaults.  RSSI thresholds are as returned by the
 * driver (dBm).  Transmit rate thresholds are IEEE rate codes (i.e
 * .5M units).
 */
#define	SCAN_VALID_DEFAULT		60	/* scan cache valid age (secs) */
#define	ROAM_RSSI_11A_DEFAULT		24	/* rssi threshold for 11a bss */
#define	ROAM_RSSI_11B_DEFAULT		24	/* rssi threshold for 11b bss */
#define	ROAM_RSSI_11BONLY_DEFAULT	24	/* rssi threshold for 11b-only bss */
#define	ROAM_RATE_11A_DEFAULT		2*24	/* tx rate threshold for 11a bss */
#define	ROAM_RATE_11B_DEFAULT		2*9	/* tx rate threshold for 11b bss */
#define	ROAM_RATE_11BONLY_DEFAULT	2*5	/* tx rate threshold for 11b-only bss */

static void scan_restart_pwrsav(unsigned long);
static void scan_next(unsigned long);

void
ieee80211_scan_attach(struct ieee80211com *ic)
{
	struct scan_state *ss;

	ic->ic_roaming = IEEE80211_ROAMING_AUTO;

	MALLOC(ss, struct scan_state *, sizeof(struct scan_state),
		M_80211_SCAN, M_NOWAIT | M_ZERO);
	if (ss != NULL) {
		init_timer(&ss->ss_scan_timer);
		ss->ss_scan_timer.function = scan_next;
		ss->ss_scan_timer.data = (unsigned long) ss;
		tasklet_init(&ss->ss_pwrsav, scan_restart_pwrsav,
			(unsigned long) ss);
		ic->ic_scan = &ss->base;
	} else
		ic->ic_scan = NULL;
}

void
ieee80211_scan_detach(struct ieee80211com *ic)
{
	struct ieee80211_scan_state *ss = ic->ic_scan;

	if (ss != NULL) {
		del_timer(&SCAN_PRIVATE(ss)->ss_scan_timer);
		tasklet_kill(&SCAN_PRIVATE(ss)->ss_pwrsav);
		if (ss->ss_ops != NULL) {
			ss->ss_ops->scan_detach(ss);
			ss->ss_ops = NULL;
		}
		ic->ic_flags &= ~IEEE80211_F_SCAN;
		ic->ic_scan = NULL;
		FREE(SCAN_PRIVATE(ss), M_80211_SCAN);
	}
}

void
ieee80211_scan_vattach(struct ieee80211vap *vap)
{
	vap->iv_bgscanidle = msecs_to_jiffies(IEEE80211_BGSCAN_IDLE_DEFAULT);
	vap->iv_bgscanintvl = IEEE80211_BGSCAN_INTVAL_DEFAULT * HZ;
	vap->iv_scanvalid = SCAN_VALID_DEFAULT * HZ;
	vap->iv_roam.rssi11a = ROAM_RSSI_11A_DEFAULT;
	vap->iv_roam.rssi11b = ROAM_RSSI_11B_DEFAULT;
	vap->iv_roam.rssi11bOnly = ROAM_RSSI_11BONLY_DEFAULT;
	vap->iv_roam.rate11a = ROAM_RATE_11A_DEFAULT;
	vap->iv_roam.rate11b = ROAM_RATE_11B_DEFAULT;
	vap->iv_roam.rate11bOnly = ROAM_RATE_11BONLY_DEFAULT;
}

void
ieee80211_scan_vdetach(struct ieee80211vap *vap)
{
	struct ieee80211com *ic = vap->iv_ic;
	struct ieee80211_scan_state *ss = ic->ic_scan;

	IEEE80211_LOCK_IRQ(ic);
	if (ss->ss_vap == vap) {
		if (ic->ic_flags & IEEE80211_F_SCAN) {
			del_timer(&SCAN_PRIVATE(ss)->ss_scan_timer);
			ic->ic_flags &= ~IEEE80211_F_SCAN;
		}
		if (ss->ss_ops != NULL) {
			ss->ss_ops->scan_detach(ss);
			ss->ss_ops = NULL;
		}
	}
	IEEE80211_UNLOCK_IRQ(ic);
}

/*
 * Simple-minded scanner module support.
 */
#define	IEEE80211_SCANNER_MAX	(IEEE80211_M_MONITOR+1)

static const char *scan_modnames[IEEE80211_SCANNER_MAX] = {
	"wlan_scan_sta",	/* IEEE80211_M_IBSS */
	"wlan_scan_sta",	/* IEEE80211_M_STA */
	"wlan_scan_wds",	/* IEEE80211_M_WDS */
	"wlan_scan_sta",	/* IEEE80211_M_AHDEMO */
	"wlan_scan_4",		/* n/a */
	"wlan_scan_5",		/* n/a */
	"wlan_scan_ap",		/* IEEE80211_M_HOSTAP */
	"wlan_scan_7",		/* n/a */
	"wlan_scan_monitor",	/* IEEE80211_M_MONITOR */
};
static const struct ieee80211_scanner *scanners[IEEE80211_SCANNER_MAX];

const struct ieee80211_scanner *
ieee80211_scanner_get(enum ieee80211_opmode mode, int tryload)
{
	int err;
	if (mode >= IEEE80211_SCANNER_MAX)
		return NULL;
	if (scanners[mode] == NULL && tryload) {
		err = ieee80211_load_module(scan_modnames[mode]);
		if (scanners[mode] == NULL || err)
			printk(KERN_WARNING "unable to load %s\n", scan_modnames[mode]);
	}
	return scanners[mode];
}
EXPORT_SYMBOL(ieee80211_scanner_get);

void
ieee80211_scanner_register(enum ieee80211_opmode mode,
	const struct ieee80211_scanner *scan)
{
	if (mode >= IEEE80211_SCANNER_MAX)
		return;
	scanners[mode] = scan;
}
EXPORT_SYMBOL(ieee80211_scanner_register);

void
ieee80211_scanner_unregister(enum ieee80211_opmode mode,
	const struct ieee80211_scanner *scan)
{
	if (mode >= IEEE80211_SCANNER_MAX)
		return;
	if (scanners[mode] == scan)
		scanners[mode] = NULL;
}
EXPORT_SYMBOL(ieee80211_scanner_unregister);

void
ieee80211_scanner_unregister_all(const struct ieee80211_scanner *scan)
{
	int m;

	for (m = 0; m < IEEE80211_SCANNER_MAX; m++)
		if (scanners[m] == scan)
			scanners[m] = NULL;
}
EXPORT_SYMBOL(ieee80211_scanner_unregister_all);

static void
change_channel(struct ieee80211com *ic,
	struct ieee80211_channel *chan)
{
	ic->ic_curchan = chan;
	ic->ic_set_channel(ic);
}

static char
channel_type(const struct ieee80211_channel *c)
{
	if (IEEE80211_IS_CHAN_ST(c))
		return 'S';
	if (IEEE80211_IS_CHAN_108A(c))
		return 'T';
	if (IEEE80211_IS_CHAN_108G(c))
		return 'G';
	if (IEEE80211_IS_CHAN_A(c))
		return 'a';
	if (IEEE80211_IS_CHAN_ANYG(c))
		return 'g';
	if (IEEE80211_IS_CHAN_B(c))
		return 'b';
	return 'f';
}

void
ieee80211_scan_dump_channels(const struct ieee80211_scan_state *ss)
{
	struct ieee80211com *ic = ss->ss_vap->iv_ic;
	const char *sep;
	int i;

	sep = "";
	for (i = ss->ss_next; i < ss->ss_last; i++) {
		const struct ieee80211_channel *c = ss->ss_chans[i];

		printf("%s%u%c", sep, ieee80211_chan2ieee(ic, c),
			channel_type(c));
		sep = ", ";
	}
}
EXPORT_SYMBOL(ieee80211_scan_dump_channels);

/*
 * Enable station power save mode and start/restart the scanning thread.
 */
static void
scan_restart_pwrsav(unsigned long arg)
{
	struct scan_state *ss = (struct scan_state *) arg;
	struct ieee80211vap *vap = ss->base.ss_vap;
	struct ieee80211com *ic = vap->iv_ic;
	int delay;

	ieee80211_sta_pwrsave(vap, 1);
	/*
	 * Use an initial 1ms delay to ensure the null
	 * data frame has a chance to go out.
	 * XXX 1ms is a lot, better to trigger scan
	 * on tx complete.
	 */
	delay = msecs_to_jiffies(1);
	if (delay < 1)
		delay = 1;
	ic->ic_scan_start(ic);			/* notify driver */
	ss->ss_scanend = jiffies + delay + ss->ss_duration;
	ss->ss_iflags |= ISCAN_START;
	mod_timer(&ss->ss_scan_timer, jiffies + delay);
}

/*
 * Start/restart scanning.  If we're operating in station mode
 * and associated notify the ap we're going into power save mode
 * and schedule a callback to initiate the work (where there's a
 * better context for doing the work).  Otherwise, start the scan
 * directly.
 */
static int
scan_restart(struct scan_state *ss, u_int duration)
{
	struct ieee80211vap *vap = ss->base.ss_vap;
	struct ieee80211com *ic = vap->iv_ic;
	int defer = 0;

	if (ss->base.ss_next == ss->base.ss_last) {
		IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
			"%s: no channels to scan\n", __func__);
		return 0;
	}
	if (vap->iv_opmode == IEEE80211_M_STA &&
	    vap->iv_state == IEEE80211_S_RUN) {
		if ((vap->iv_bss->ni_flags & IEEE80211_NODE_PWR_MGT) == 0) {
			/*
			 * Initiate power save before going off-channel.
			 * Note that we cannot do this directly because
			 * of locking issues; instead we defer it to a
			 * tasklet.
			 */
			ss->ss_duration = duration;
			tasklet_schedule(&ss->ss_pwrsav);
			defer = 1;
		}
	}

	if (!defer) {
		ic->ic_scan_start(ic);		/* notify driver */
		ss->ss_scanend = jiffies + duration;
		ss->ss_iflags |= ISCAN_START;
		mod_timer(&ss->ss_scan_timer, jiffies);
	}
	return 1;
}

static void
copy_ssid(struct ieee80211vap *vap, struct ieee80211_scan_state *ss,
	int nssid, const struct ieee80211_scan_ssid ssids[])
{
	if (nssid > IEEE80211_SCAN_MAX_SSID) {
		/* XXX printf */
		IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
			"%s: too many ssid %d, ignoring all of them\n",
			__func__, nssid);
		return;
	}
	memcpy(ss->ss_ssid, ssids, nssid * sizeof(ssids[0]));
	ss->ss_nssid = nssid;
}

/*
 * Start a scan unless one is already going.
 */
int
ieee80211_start_scan(struct ieee80211vap *vap, int flags, u_int duration,
	u_int nssid, const struct ieee80211_scan_ssid ssids[])
{
	struct ieee80211com *ic = vap->iv_ic;
	const struct ieee80211_scanner *scan;
	struct ieee80211_scan_state *ss = ic->ic_scan;

	scan = ieee80211_scanner_get(vap->iv_opmode, 0);
	if (scan == NULL) {
		IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
			"%s: no scanner support for mode %u\n",
			__func__, vap->iv_opmode);
		/* XXX stat */
		return 0;
	}

	IEEE80211_LOCK_IRQ(ic);
	if ((ic->ic_flags & IEEE80211_F_SCAN) == 0) {
		IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
			"%s: %s scan, duration %lu, desired mode %s, %s%s%s%s\n",
			__func__,
			flags & IEEE80211_SCAN_ACTIVE ? "active" : "passive",
		 	duration,
			ieee80211_phymode_name[vap->iv_des_mode],
			flags & IEEE80211_SCAN_FLUSH ? "flush" : "append",
			flags & IEEE80211_SCAN_NOPICK ? ", nopick" : "",
			flags & IEEE80211_SCAN_PICK1ST ? ", pick1st" : "",
			flags & IEEE80211_SCAN_ONCE ? ", once" : "");

		ss->ss_vap = vap;
		if (ss->ss_ops != scan) {
			/* switch scanners; detach old, attach new */
			if (ss->ss_ops != NULL)
				ss->ss_ops->scan_detach(ss);
			if (!scan->scan_attach(ss)) {
				/* XXX attach failure */
				/* XXX stat+msg */
				ss->ss_ops = NULL;
			} else
				ss->ss_ops = scan;
		}
		if (ss->ss_ops != NULL) {
			if ((flags & IEEE80211_SCAN_NOSSID) == 0)
				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);

			/* NB: flush frames rx'd before 1st channel change */
			SCAN_PRIVATE(ss)->ss_iflags |= ISCAN_DISCARD;
			ss->ss_ops->scan_start(ss, vap);
			if (scan_restart(SCAN_PRIVATE(ss), duration))
				ic->ic_flags |= IEEE80211_F_SCAN;
		}
	} 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_IRQ(ic);

	/* NB: racey, does it matter? */
	return (ic->ic_flags & IEEE80211_F_SCAN);
}
EXPORT_SYMBOL(ieee80211_start_scan);

/*
 * Check the scan cache for an ap/channel to use; if that
 * fails then kick off a new scan.
 */
int
ieee80211_check_scan(struct ieee80211vap *vap, int flags, u_int duration,
	u_int nssid, const struct ieee80211_scan_ssid ssids[],
	int (*action)(struct ieee80211vap *, const struct ieee80211_scan_entry *))
{
	struct ieee80211com *ic = vap->iv_ic;
	struct ieee80211_scan_state *ss = ic->ic_scan;
	int checkscanlist = 0;

	/*
	 * Check if there's a list of scan candidates already.
	 * XXX want more than the ap we're currently associated with
	 */
	IEEE80211_LOCK_IRQ(ic);
	IEEE80211_DPRINTF(vap, IEEE80211_MSG_SCAN,
		"%s: %s scan, duration %lu, desired mode %s, %s%s%s%s\n",
		__func__,
		flags & IEEE80211_SCAN_ACTIVE ? "active" : "passive",
		duration,
		ieee80211_phymode_name[vap->iv_des_mode],
		flags & IEEE80211_SCAN_FLUSH ? "flush" : "append",
		flags & IEEE80211_SCAN_NOPICK ? ", nopick" : "",
		flags & IEEE80211_SCAN_PICK1ST ? ", pick1st" : "",
		flags & IEEE80211_SCAN_ONCE ? ", once" : "",
		flags & IEEE80211_SCAN_USECACHE ? ", usecache" : "");

	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.
			 */
			copy_ssid(vap, ss, nssid, ssids);
			flags |= IEEE80211_SCAN_NOSSID;
		}
		if ((ic->ic_flags & IEEE80211_F_SCAN) == 0 &&
		     time_before(jiffies, 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;
			checkscanlist = 1;
		}
	}
	IEEE80211_UNLOCK_IRQ(ic);
	if (checkscanlist) {
		/*
		 * ss must be filled out so scan may be restarted "outside"
		 * of the current callstack.
		 */
		ss->ss_flags = flags;
		ss->ss_duration = duration;
		if (ss->ss_ops->scan_end(ss, ss->ss_vap, action, flags & IEEE80211_SCAN_KEEPMODE)) {
			/* found an ap, just clear the flag */
			ic->ic_flags &= ~IEEE80211_F_SCAN;
			return 1;
		}
		/* no ap, clear the flag before starting a scan */