mac80211: use nl80211 interface types

[mirror_ubuntu-bionic-kernel.git] / net / mac80211 / sta_info.c

/*
 * Copyright 2002-2005, Instant802 Networks, Inc.
 * Copyright 2006-2007  Jiri Benc <jbenc@suse.cz>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/netdevice.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/skbuff.h>
#include <linux/if_arp.h>
#include <linux/timer.h>
#include <linux/rtnetlink.h>

#include <net/mac80211.h>
#include "ieee80211_i.h"
#include "rate.h"
#include "sta_info.h"
#include "debugfs_sta.h"
#include "mesh.h"

/**
 * DOC: STA information lifetime rules
 *
 * STA info structures (&struct sta_info) are managed in a hash table
 * for faster lookup and a list for iteration. They are managed using
 * RCU, i.e. access to the list and hash table is protected by RCU.
 *
 * Upon allocating a STA info structure with sta_info_alloc(), the caller owns
 * that structure. It must then either destroy it using sta_info_destroy()
 * (which is pretty useless) or insert it into the hash table using
 * sta_info_insert() which demotes the reference from ownership to a regular
 * RCU-protected reference; if the function is called without protection by an
 * RCU critical section the reference is instantly invalidated. Note that the
 * caller may not do much with the STA info before inserting it, in particular,
 * it may not start any mesh peer link management or add encryption keys.
 *
 * When the insertion fails (sta_info_insert()) returns non-zero), the
 * structure will have been freed by sta_info_insert()!
 *
 * Because there are debugfs entries for each station, and adding those
 * must be able to sleep, it is also possible to "pin" a station entry,
 * that means it can be removed from the hash table but not be freed.
 * See the comment in __sta_info_unlink() for more information, this is
 * an internal capability only.
 *
 * In order to remove a STA info structure, the caller needs to first
 * unlink it (sta_info_unlink()) from the list and hash tables and
 * then destroy it; sta_info_destroy() will wait for an RCU grace period
 * to elapse before actually freeing it. Due to the pinning and the
 * possibility of multiple callers trying to remove the same STA info at
 * the same time, sta_info_unlink() can clear the STA info pointer it is
 * passed to indicate that the STA info is owned by somebody else now.
 *
 * If sta_info_unlink() did not clear the pointer then the caller owns
 * the STA info structure now and is responsible of destroying it with
 * a call to sta_info_destroy().
 *
 * In all other cases, there is no concept of ownership on a STA entry,
 * each structure is owned by the global hash table/list until it is
 * removed. All users of the structure need to be RCU protected so that
 * the structure won't be freed before they are done using it.
 */

/* Caller must hold local->sta_lock */
static int sta_info_hash_del(struct ieee80211_local *local,
                             struct sta_info *sta)
{
        struct sta_info *s;

        s = local->sta_hash[STA_HASH(sta->addr)];
        if (!s)
                return -ENOENT;
        if (s == sta) {
                rcu_assign_pointer(local->sta_hash[STA_HASH(sta->addr)],
                                   s->hnext);
                return 0;
        }

        while (s->hnext && s->hnext != sta)
                s = s->hnext;
        if (s->hnext) {
                rcu_assign_pointer(s->hnext, sta->hnext);
                return 0;
        }

        return -ENOENT;
}

/* protected by RCU */
static struct sta_info *__sta_info_find(struct ieee80211_local *local,
                                        u8 *addr)
{
        struct sta_info *sta;

        sta = rcu_dereference(local->sta_hash[STA_HASH(addr)]);
        while (sta) {
                if (compare_ether_addr(sta->addr, addr) == 0)
                        break;
                sta = rcu_dereference(sta->hnext);
        }
        return sta;
}

struct sta_info *sta_info_get(struct ieee80211_local *local, u8 *addr)
{
        return __sta_info_find(local, addr);
}
EXPORT_SYMBOL(sta_info_get);

struct sta_info *sta_info_get_by_idx(struct ieee80211_local *local, int idx,
                                     struct net_device *dev)
{
        struct sta_info *sta;
        int i = 0;

        list_for_each_entry_rcu(sta, &local->sta_list, list) {
                if (dev && dev != sta->sdata->dev)
                        continue;
                if (i < idx) {
                        ++i;
                        continue;
                }
                return sta;
        }

        return NULL;
}

/**
 * __sta_info_free - internal STA free helper
 *
 * @local: pointer to the global information
 * @sta: STA info to free
 *
 * This function must undo everything done by sta_info_alloc()
 * that may happen before sta_info_insert().
 */
static void __sta_info_free(struct ieee80211_local *local,
                            struct sta_info *sta)
{
        DECLARE_MAC_BUF(mbuf);

        rate_control_free_sta(sta->rate_ctrl, sta->rate_ctrl_priv);
        rate_control_put(sta->rate_ctrl);

#ifdef CONFIG_MAC80211_VERBOSE_DEBUG
        printk(KERN_DEBUG "%s: Destroyed STA %s\n",
               wiphy_name(local->hw.wiphy), print_mac(mbuf, sta->addr));
#endif /* CONFIG_MAC80211_VERBOSE_DEBUG */

        kfree(sta);
}

void sta_info_destroy(struct sta_info *sta)
{
        struct ieee80211_local *local;
        struct sk_buff *skb;
        int i;

        might_sleep();

        if (!sta)
                return;

        local = sta->local;

        rate_control_remove_sta_debugfs(sta);
        ieee80211_sta_debugfs_remove(sta);

#ifdef CONFIG_MAC80211_MESH
        if (ieee80211_vif_is_mesh(&sta->sdata->vif))
                mesh_plink_deactivate(sta);
#endif

        /*
         * We have only unlinked the key, and actually destroying it
         * may mean it is removed from hardware which requires that
         * the key->sta pointer is still valid, so flush the key todo
         * list here.
         *
         * ieee80211_key_todo() will synchronize_rcu() so after this
         * nothing can reference this sta struct any more.
         */
        ieee80211_key_todo();

#ifdef CONFIG_MAC80211_MESH
        if (ieee80211_vif_is_mesh(&sta->sdata->vif))
                del_timer_sync(&sta->plink_timer);
#endif

        while ((skb = skb_dequeue(&sta->ps_tx_buf)) != NULL) {
                local->total_ps_buffered--;
                dev_kfree_skb_any(skb);
        }

        while ((skb = skb_dequeue(&sta->tx_filtered)) != NULL)
                dev_kfree_skb_any(skb);

        for (i = 0; i <  STA_TID_NUM; i++) {
                spin_lock_bh(&sta->lock);
                if (sta->ampdu_mlme.tid_rx[i])
                  del_timer_sync(&sta->ampdu_mlme.tid_rx[i]->session_timer);
                if (sta->ampdu_mlme.tid_tx[i])
                  del_timer_sync(&sta->ampdu_mlme.tid_tx[i]->addba_resp_timer);
                spin_unlock_bh(&sta->lock);
        }

        __sta_info_free(local, sta);
}


/* Caller must hold local->sta_lock */
static void sta_info_hash_add(struct ieee80211_local *local,
                              struct sta_info *sta)
{
        sta->hnext = local->sta_hash[STA_HASH(sta->addr)];
        rcu_assign_pointer(local->sta_hash[STA_HASH(sta->addr)], sta);
}

struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
                                u8 *addr, gfp_t gfp)
{
        struct ieee80211_local *local = sdata->local;
        struct sta_info *sta;
        int i;
        DECLARE_MAC_BUF(mbuf);

        sta = kzalloc(sizeof(*sta), gfp);
        if (!sta)
                return NULL;

        spin_lock_init(&sta->lock);
        spin_lock_init(&sta->flaglock);

        memcpy(sta->addr, addr, ETH_ALEN);
        sta->local = local;
        sta->sdata = sdata;

        sta->rate_ctrl = rate_control_get(local->rate_ctrl);
        sta->rate_ctrl_priv = rate_control_alloc_sta(sta->rate_ctrl,
                                                     gfp);
        if (!sta->rate_ctrl_priv) {
                rate_control_put(sta->rate_ctrl);
                kfree(sta);
                return NULL;
        }

        for (i = 0; i < STA_TID_NUM; i++) {
                /* timer_to_tid must be initialized with identity mapping to
                 * enable session_timer's data differentiation. refer to
                 * sta_rx_agg_session_timer_expired for useage */
                sta->timer_to_tid[i] = i;
                /* tid to tx queue: initialize according to HW (0 is valid) */
                sta->tid_to_tx_q[i] = ieee80211_num_queues(&local->hw);
                /* rx */
                sta->ampdu_mlme.tid_state_rx[i] = HT_AGG_STATE_IDLE;
                sta->ampdu_mlme.tid_rx[i] = NULL;
                /* tx */
                sta->ampdu_mlme.tid_state_tx[i] = HT_AGG_STATE_IDLE;
                sta->ampdu_mlme.tid_tx[i] = NULL;
                sta->ampdu_mlme.addba_req_num[i] = 0;
        }
        skb_queue_head_init(&sta->ps_tx_buf);
        skb_queue_head_init(&sta->tx_filtered);

#ifdef CONFIG_MAC80211_VERBOSE_DEBUG
        printk(KERN_DEBUG "%s: Allocated STA %s\n",
               wiphy_name(local->hw.wiphy), print_mac(mbuf, sta->addr));
#endif /* CONFIG_MAC80211_VERBOSE_DEBUG */

#ifdef CONFIG_MAC80211_MESH
        sta->plink_state = PLINK_LISTEN;
        init_timer(&sta->plink_timer);
#endif

        return sta;
}

int sta_info_insert(struct sta_info *sta)
{
        struct ieee80211_local *local = sta->local;
        struct ieee80211_sub_if_data *sdata = sta->sdata;
        unsigned long flags;
        int err = 0;
        DECLARE_MAC_BUF(mac);

        /*
         * Can't be a WARN_ON because it can be triggered through a race:
         * something inserts a STA (on one CPU) without holding the RTNL
         * and another CPU turns off the net device.
         */
        if (unlikely(!netif_running(sdata->dev))) {
                err = -ENETDOWN;
                goto out_free;
        }

        if (WARN_ON(compare_ether_addr(sta->addr, sdata->dev->dev_addr) == 0 ||
                    is_multicast_ether_addr(sta->addr))) {
                err = -EINVAL;
                goto out_free;
        }

        spin_lock_irqsave(&local->sta_lock, flags);
        /* check if STA exists already */
        if (__sta_info_find(local, sta->addr)) {
                spin_unlock_irqrestore(&local->sta_lock, flags);
                err = -EEXIST;
                goto out_free;
        }
        list_add(&sta->list, &local->sta_list);
        local->num_sta++;
        sta_info_hash_add(local, sta);

        /* notify driver */
        if (local->ops->sta_notify) {
                if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
                        sdata = container_of(sdata->bss,
                                             struct ieee80211_sub_if_data,
                                             u.ap);

                local->ops->sta_notify(local_to_hw(local), &sdata->vif,
                                       STA_NOTIFY_ADD, sta->addr);
        }

#ifdef CONFIG_MAC80211_VERBOSE_DEBUG
        printk(KERN_DEBUG "%s: Inserted STA %s\n",
               wiphy_name(local->hw.wiphy), print_mac(mac, sta->addr));
#endif /* CONFIG_MAC80211_VERBOSE_DEBUG */

        spin_unlock_irqrestore(&local->sta_lock, flags);

#ifdef CONFIG_MAC80211_DEBUGFS
        /*
         * Debugfs entry adding might sleep, so schedule process
         * context task for adding entry for STAs that do not yet
         * have one.
         * NOTE: due to auto-freeing semantics this may only be done
         *       if the insertion is successful!
         */
        schedule_work(&local->sta_debugfs_add);
#endif

        if (ieee80211_vif_is_mesh(&sdata->vif))
                mesh_accept_plinks_update(sdata);

        return 0;
 out_free:
        BUG_ON(!err);
        __sta_info_free(local, sta);
        return err;
}

static inline void __bss_tim_set(struct ieee80211_if_ap *bss, u16 aid)
{
        /*
         * This format has been mandated by the IEEE specifications,
         * so this line may not be changed to use the __set_bit() format.
         */
        bss->tim[aid / 8] |= (1 << (aid % 8));
}

static inline void __bss_tim_clear(struct ieee80211_if_ap *bss, u16 aid)
{
        /*
         * This format has been mandated by the IEEE specifications,
         * so this line may not be changed to use the __clear_bit() format.
         */
        bss->tim[aid / 8] &= ~(1 << (aid % 8));
}

static void __sta_info_set_tim_bit(struct ieee80211_if_ap *bss,
                                   struct sta_info *sta)
{
        BUG_ON(!bss);

        __bss_tim_set(bss, sta->aid);

        if (sta->local->ops->set_tim) {
                sta->local->tim_in_locked_section = true;
                sta->local->ops->set_tim(local_to_hw(sta->local), sta->aid, 1);
                sta->local->tim_in_locked_section = false;
        }
}

void sta_info_set_tim_bit(struct sta_info *sta)
{
        unsigned long flags;

        BUG_ON(!sta->sdata->bss);

        spin_lock_irqsave(&sta->local->sta_lock, flags);
        __sta_info_set_tim_bit(sta->sdata->bss, sta);
        spin_unlock_irqrestore(&sta->local->sta_lock, flags);
}

static void __sta_info_clear_tim_bit(struct ieee80211_if_ap *bss,
                                     struct sta_info *sta)
{
        BUG_ON(!bss);

        __bss_tim_clear(bss, sta->aid);

        if (sta->local->ops->set_tim) {
                sta->local->tim_in_locked_section = true;
                sta->local->ops->set_tim(local_to_hw(sta->local), sta->aid, 0);
                sta->local->tim_in_locked_section = false;
        }
}

void sta_info_clear_tim_bit(struct sta_info *sta)
{
        unsigned long flags;

        BUG_ON(!sta->sdata->bss);

        spin_lock_irqsave(&sta->local->sta_lock, flags);
        __sta_info_clear_tim_bit(sta->sdata->bss, sta);
        spin_unlock_irqrestore(&sta->local->sta_lock, flags);
}

static void __sta_info_unlink(struct sta_info **sta)
{
        struct ieee80211_local *local = (*sta)->local;
        struct ieee80211_sub_if_data *sdata = (*sta)->sdata;
#ifdef CONFIG_MAC80211_VERBOSE_DEBUG
        DECLARE_MAC_BUF(mbuf);
#endif
        /*
         * pull caller's reference if we're already gone.
         */
        if (sta_info_hash_del(local, *sta)) {
                *sta = NULL;
                return;
        }

        if ((*sta)->key) {
                ieee80211_key_free((*sta)->key);
                WARN_ON((*sta)->key);
        }

        list_del(&(*sta)->list);

        if (test_and_clear_sta_flags(*sta, WLAN_STA_PS)) {
                BUG_ON(!sdata->bss);

                atomic_dec(&sdata->bss->num_sta_ps);
                __sta_info_clear_tim_bit(sdata->bss, *sta);
        }

        local->num_sta--;

        if (local->ops->sta_notify) {
                if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
                        sdata = container_of(sdata->bss,
                                             struct ieee80211_sub_if_data,
                                             u.ap);

                local->ops->sta_notify(local_to_hw(local), &sdata->vif,
                                       STA_NOTIFY_REMOVE, (*sta)->addr);
        }

        if (ieee80211_vif_is_mesh(&sdata->vif)) {
                mesh_accept_plinks_update(sdata);
#ifdef CONFIG_MAC80211_MESH
                del_timer(&(*sta)->plink_timer);
#endif
        }

#ifdef CONFIG_MAC80211_VERBOSE_DEBUG
        printk(KERN_DEBUG "%s: Removed STA %s\n",
               wiphy_name(local->hw.wiphy), print_mac(mbuf, (*sta)->addr));
#endif /* CONFIG_MAC80211_VERBOSE_DEBUG */

        /*
         * Finally, pull caller's reference if the STA is pinned by the
         * task that is adding the debugfs entries. In that case, we
         * leave the STA "to be freed".
         *
         * The rules are not trivial, but not too complex either:
         *  (1) pin_status is only modified under the sta_lock
         *  (2) STAs may only be pinned under the RTNL so that
         *      sta_info_flush() is guaranteed to actually destroy
         *      all STAs that are active for a given interface, this
         *      is required for correctness because otherwise we
         *      could notify a driver that an interface is going
         *      away and only after that (!) notify it about a STA
         *      on that interface going away.
         *  (3) sta_info_debugfs_add_work() will set the status
         *      to PINNED when it found an item that needs a new
         *      debugfs directory created. In that case, that item
         *      must not be freed although all *RCU* users are done
         *      with it. Hence, we tell the caller of _unlink()
         *      that the item is already gone (as can happen when
         *      two tasks try to unlink/destroy at the same time)
         *  (4) We set the pin_status to DESTROY here when we
         *      find such an item.
         *  (5) sta_info_debugfs_add_work() will reset the pin_status
         *      from PINNED to NORMAL when it is done with the item,
         *      but will check for DESTROY before resetting it in
         *      which case it will free the item.
         */
        if ((*sta)->pin_status == STA_INFO_PIN_STAT_PINNED) {
                (*sta)->pin_status = STA_INFO_PIN_STAT_DESTROY;
                *sta = NULL;
                return;
        }
}

void sta_info_unlink(struct sta_info **sta)
{
        struct ieee80211_local *local = (*sta)->local;
        unsigned long flags;

        spin_lock_irqsave(&local->sta_lock, flags);
        __sta_info_unlink(sta);
        spin_unlock_irqrestore(&local->sta_lock, flags);
}

static inline int sta_info_buffer_expired(struct ieee80211_local *local,
                                          struct sta_info *sta,
                                          struct sk_buff *skb)
{
        struct ieee80211_tx_info *info;
        int timeout;

        if (!skb)
                return 0;

        info = IEEE80211_SKB_CB(skb);

        /* Timeout: (2 * listen_interval * beacon_int * 1024 / 1000000) sec */
        timeout = (sta->listen_interval * local->hw.conf.beacon_int * 32 /
                   15625) * HZ;
        if (timeout < STA_TX_BUFFER_EXPIRE)
                timeout = STA_TX_BUFFER_EXPIRE;
        return time_after(jiffies, info->control.jiffies + timeout);
}


static void sta_info_cleanup_expire_buffered(struct ieee80211_local *local,
                                             struct sta_info *sta)
{
        unsigned long flags;
        struct sk_buff *skb;
        struct ieee80211_sub_if_data *sdata;
        DECLARE_MAC_BUF(mac);

        if (skb_queue_empty(&sta->ps_tx_buf))
                return;

        for (;;) {
                spin_lock_irqsave(&sta->ps_tx_buf.lock, flags);
                skb = skb_peek(&sta->ps_tx_buf);
                if (sta_info_buffer_expired(local, sta, skb))
                        skb = __skb_dequeue(&sta->ps_tx_buf);
                else
                        skb = NULL;
                spin_unlock_irqrestore(&sta->ps_tx_buf.lock, flags);

                if (!skb)
                        break;

                sdata = sta->sdata;
                local->total_ps_buffered--;
#ifdef CONFIG_MAC80211_VERBOSE_PS_DEBUG
                printk(KERN_DEBUG "Buffered frame expired (STA "
                       "%s)\n", print_mac(mac, sta->addr));
#endif
                dev_kfree_skb(skb);

                if (skb_queue_empty(&sta->ps_tx_buf))
                        sta_info_clear_tim_bit(sta);
        }
}


static void sta_info_cleanup(unsigned long data)
{
        struct ieee80211_local *local = (struct ieee80211_local *) data;
        struct sta_info *sta;

        rcu_read_lock();
        list_for_each_entry_rcu(sta, &local->sta_list, list)
                sta_info_cleanup_expire_buffered(local, sta);
        rcu_read_unlock();

        local->sta_cleanup.expires =
                round_jiffies(jiffies + STA_INFO_CLEANUP_INTERVAL);
        add_timer(&local->sta_cleanup);
}

#ifdef CONFIG_MAC80211_DEBUGFS
/*
 * See comment in __sta_info_unlink,
 * caller must hold local->sta_lock.
 */
static void __sta_info_pin(struct sta_info *sta)
{
        WARN_ON(sta->pin_status != STA_INFO_PIN_STAT_NORMAL);
        sta->pin_status = STA_INFO_PIN_STAT_PINNED;
}

/*
 * See comment in __sta_info_unlink, returns sta if it
 * needs to be destroyed.
 */
static struct sta_info *__sta_info_unpin(struct sta_info *sta)
{
        struct sta_info *ret = NULL;
        unsigned long flags;

        spin_lock_irqsave(&sta->local->sta_lock, flags);
        WARN_ON(sta->pin_status != STA_INFO_PIN_STAT_DESTROY &&
                sta->pin_status != STA_INFO_PIN_STAT_PINNED);
        if (sta->pin_status == STA_INFO_PIN_STAT_DESTROY)
                ret = sta;
        sta->pin_status = STA_INFO_PIN_STAT_NORMAL;
        spin_unlock_irqrestore(&sta->local->sta_lock, flags);

        return ret;
}

static void sta_info_debugfs_add_work(struct work_struct *work)
{
        struct ieee80211_local *local =
                container_of(work, struct ieee80211_local, sta_debugfs_add);
        struct sta_info *sta, *tmp;
        unsigned long flags;

        /* We need to keep the RTNL across the whole pinned status. */
        rtnl_lock();
        while (1) {
                sta = NULL;

                spin_lock_irqsave(&local->sta_lock, flags);
                list_for_each_entry(tmp, &local->sta_list, list) {
                        if (!tmp->debugfs.dir) {
                                sta = tmp;
                                __sta_info_pin(sta);
                                break;
                        }
                }
                spin_unlock_irqrestore(&local->sta_lock, flags);

                if (!sta)
                        break;

                ieee80211_sta_debugfs_add(sta);
                rate_control_add_sta_debugfs(sta);

                sta = __sta_info_unpin(sta);
                sta_info_destroy(sta);
        }
        rtnl_unlock();
}
#endif

static void __ieee80211_run_pending_flush(struct ieee80211_local *local)
{
        struct sta_info *sta;
        unsigned long flags;

        ASSERT_RTNL();

        spin_lock_irqsave(&local->sta_lock, flags);
        while (!list_empty(&local->sta_flush_list)) {
                sta = list_first_entry(&local->sta_flush_list,
                                       struct sta_info, list);
                list_del(&sta->list);
                spin_unlock_irqrestore(&local->sta_lock, flags);
                sta_info_destroy(sta);
                spin_lock_irqsave(&local->sta_lock, flags);
        }
        spin_unlock_irqrestore(&local->sta_lock, flags);
}

static void ieee80211_sta_flush_work(struct work_struct *work)
{
        struct ieee80211_local *local =
                container_of(work, struct ieee80211_local, sta_flush_work);

        rtnl_lock();
        __ieee80211_run_pending_flush(local);
        rtnl_unlock();
}

void sta_info_init(struct ieee80211_local *local)
{
        spin_lock_init(&local->sta_lock);
        INIT_LIST_HEAD(&local->sta_list);
        INIT_LIST_HEAD(&local->sta_flush_list);
        INIT_WORK(&local->sta_flush_work, ieee80211_sta_flush_work);

        setup_timer(&local->sta_cleanup, sta_info_cleanup,
                    (unsigned long)local);
        local->sta_cleanup.expires =
                round_jiffies(jiffies + STA_INFO_CLEANUP_INTERVAL);

#ifdef CONFIG_MAC80211_DEBUGFS
        INIT_WORK(&local->sta_debugfs_add, sta_info_debugfs_add_work);
#endif
}

int sta_info_start(struct ieee80211_local *local)
{
        add_timer(&local->sta_cleanup);
        return 0;
}

void sta_info_stop(struct ieee80211_local *local)
{
        del_timer(&local->sta_cleanup);
        cancel_work_sync(&local->sta_flush_work);
#ifdef CONFIG_MAC80211_DEBUGFS
        /*
         * Make sure the debugfs adding work isn't pending after this
         * because we're about to be destroyed. It doesn't matter
         * whether it ran or not since we're going to flush all STAs
         * anyway.
         */
        cancel_work_sync(&local->sta_debugfs_add);
#endif

        rtnl_lock();
        sta_info_flush(local, NULL);
        __ieee80211_run_pending_flush(local);
        rtnl_unlock();
}

/**
 * sta_info_flush - flush matching STA entries from the STA table
 *
 * Returns the number of removed STA entries.
 *
 * @local: local interface data
 * @sdata: matching rule for the net device (sta->dev) or %NULL to match all STAs
 */
int sta_info_flush(struct ieee80211_local *local,
                    struct ieee80211_sub_if_data *sdata)
{
        struct sta_info *sta, *tmp;
        LIST_HEAD(tmp_list);
        int ret = 0;
        unsigned long flags;

        might_sleep();
        ASSERT_RTNL();

        spin_lock_irqsave(&local->sta_lock, flags);
        list_for_each_entry_safe(sta, tmp, &local->sta_list, list) {
                if (!sdata || sdata == sta->sdata) {
                        __sta_info_unlink(&sta);
                        if (sta) {
                                list_add_tail(&sta->list, &tmp_list);
                                ret++;
                        }
                }
        }
        spin_unlock_irqrestore(&local->sta_lock, flags);

        list_for_each_entry_safe(sta, tmp, &tmp_list, list)
                sta_info_destroy(sta);

        return ret;
}

/**
 * sta_info_flush_delayed - flush matching STA entries from the STA table
 *
 * This function unlinks all stations for a given interface and queues
 * them for freeing. Note that the workqueue function scheduled here has
 * to run before any new keys can be added to the system to avoid set_key()
 * callback ordering issues.
 *
 * @sdata: the interface
 */
void sta_info_flush_delayed(struct ieee80211_sub_if_data *sdata)
{
        struct ieee80211_local *local = sdata->local;
        struct sta_info *sta, *tmp;
        unsigned long flags;
        bool work = false;

        spin_lock_irqsave(&local->sta_lock, flags);
        list_for_each_entry_safe(sta, tmp, &local->sta_list, list) {
                if (sdata == sta->sdata) {
                        __sta_info_unlink(&sta);
                        if (sta) {
                                list_add_tail(&sta->list,
                                              &local->sta_flush_list);
                                work = true;
                        }
                }
        }
        if (work)
                schedule_work(&local->sta_flush_work);
        spin_unlock_irqrestore(&local->sta_lock, flags);
}

void ieee80211_sta_expire(struct ieee80211_sub_if_data *sdata,
                          unsigned long exp_time)
{
        struct ieee80211_local *local = sdata->local;
        struct sta_info *sta, *tmp;
        LIST_HEAD(tmp_list);
        DECLARE_MAC_BUF(mac);
        unsigned long flags;

        spin_lock_irqsave(&local->sta_lock, flags);
        list_for_each_entry_safe(sta, tmp, &local->sta_list, list)
                if (time_after(jiffies, sta->last_rx + exp_time)) {
#ifdef CONFIG_MAC80211_IBSS_DEBUG
                        printk(KERN_DEBUG "%s: expiring inactive STA %s\n",
                               sdata->dev->name, print_mac(mac, sta->addr));
#endif
                        __sta_info_unlink(&sta);
                        if (sta)
                                list_add(&sta->list, &tmp_list);
                }
        spin_unlock_irqrestore(&local->sta_lock, flags);

        list_for_each_entry_safe(sta, tmp, &tmp_list, list)
                sta_info_destroy(sta);
}