OpenWRT数据接收过程

1. ieee80211_tasklet_handler()

Linux内核是通过中断来对接收到的数据进行响应的。当硬件检测到有接收数据的时候，产生一个中断，中断触发下半部的tasklet机制，在802.11协议栈这里会调用ieee80211_tasklet_handler()函数。我们来看一看函数体：（位于OpenWRT内核文件夹子目录/net/mac80211，文件main.c中）

static void ieee80211_tasklet_handler(unsigned long data){ struct ieee80211_local *local = (struct ieee80211_local *) data; struct sk_buff *skb; while ((skb = skb_dequeue(&local->skb_queue)) || (skb = skb_dequeue(&local->skb_queue_unreliable))) { switch (skb->pkt_type) { case IEEE80211_RX_MSG: /* Clear skb->pkt_type in order to not confuse kernel * netstack. */ skb->pkt_type = 0; ieee80211_rx(&local->hw, skb); break; case IEEE80211_TX_STATUS_MSG: ... default: ... } }}

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2. ieee80211_rx()

系统收到数据时会开辟一个sk_buff缓存空间进行数据的存储，ieee80211_tasklet_handler()触发后对sk_buff中存储的数据帧进行判断，如果是接收来的数据（MPDU），则进入ieee80211_rx()函数：（位于OpenWRT内核文件夹子目录/net/mac80211，文件rx.c中）。

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void ieee80211_rx(struct ieee80211_hw *hw, struct sk_buff *skb){ struct ieee80211_local *local = hw_to_local(hw); struct ieee80211_rate *rate = NULL; struct ieee80211_supported_band *sband; struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb); ... __ieee80211_rx_handle_packet(hw, skb); rcu_read_unlock(); return; drop: kfree_skb(skb);}EXPORT_SYMBOL(ieee80211_rx);

3. __ieee80211_rx_handle_packet()

ieee80211_rx()函数再调用__ieee80211_rx_handle_packet()（位于OpenWRT内核文件夹子目录/net/mac80211，文件rx.c中），__ieee80211_rx_handle_packet()是接收帧的处理函数，会对帧类型进行判断，如果检测出该帧是beacon帧（或sta主动扫描后从AP端返回的响应帧），则进入ieee80211_scan_rx()函数对帧信息进行扫描，如果是数据帧，则调用ieee80211_prepare_and_rx_handle()对帧进行处理，下面分析接收帧为数据帧的情况。

4. ieee80211_prepare_and_rx_handle()

调用ieee80211_prepare_and_rx_handle()（位于OpenWRT内核文件夹子目录/net/mac80211，文件rx.c中）。

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/* * This function returns whether or not the SKB * was destined for RX processing or not, which, * if consume is true, is equivalent to whether * or not the skb was consumed. */static bool ieee80211_prepare_and_rx_handle(struct ieee80211_rx_data *rx, struct sk_buff *skb, bool consume){… ieee80211_invoke_rx_handlers(rx); return true;}

5. ieee80211_invoke_rx_handlers()

调用ieee80211_invoke_rx_handlers()（位于OpenWRT内核文件夹子目录/net/mac80211，文件rx.c中）。

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static void ieee80211_invoke_rx_handlers(struct ieee80211_rx_data *rx){… ieee80211_rx_reorder_ampdu(rx, &reorder_release); ieee80211_rx_handlers(rx, &reorder_release); return; rxh_next: ieee80211_rx_handlers_result(rx, res);…}

6. ieee80211_rx_handlers()

调用ieee80211_rx_handlers()（位于OpenWRT内核文件夹子目录/net/mac80211，文件rx.c中）。

static void ieee80211_rx_handlers(struct ieee80211_rx_data *rx, struct sk_buff_head *frames){ ieee80211_rx_result res = RX_DROP_MONITOR; struct sk_buff *skb;#define CALL_RXH(rxh) do { res = rxh(rx); if (res != RX_CONTINUE) goto rxh_next; } while (0); spin_lock_bh(&rx->local->rx_path_lock); while ((skb = __skb_dequeue(frames))) { /* * all the other fields are valid across frames * that belong to an aMPDU since they are on the * same TID from the same station */ rx->skb = skb; CALL_RXH(ieee80211_rx_h_decrypt) CALL_RXH(ieee80211_rx_h_check_more_data) CALL_RXH(ieee80211_rx_h_uapsd_and_pspoll) CALL_RXH(ieee80211_rx_h_sta_process) CALL_RXH(ieee80211_rx_h_defragment) CALL_RXH(ieee80211_rx_h_michael_mic_verify) /* must be after MMIC verify so header is counted in MPDU mic */#ifdef CPTCFG_MAC80211_MESH if (ieee80211_vif_is_mesh(&rx->sdata->vif)) CALL_RXH(ieee80211_rx_h_mesh_fwding);#endif CALL_RXH(ieee80211_rx_h_amsdu) CALL_RXH(ieee80211_rx_h_data) /* special treatment -- needs the queue */ res = ieee80211_rx_h_ctrl(rx, frames); if (res != RX_CONTINUE) goto rxh_next; CALL_RXH(ieee80211_rx_h_mgmt_check) CALL_RXH(ieee80211_rx_h_action) CALL_RXH(ieee80211_rx_h_userspace_mgmt) CALL_RXH(ieee80211_rx_h_action_return) CALL_RXH(ieee80211_rx_h_mgmt) rxh_next: ieee80211_rx_handlers_result(rx, res);#undef CALL_RXH } spin_unlock_bh(&rx->local->rx_path_lock);}

7. ieee80211_rx_h_data()

只看是数据帧的情况，会继续调用ieee80211_rx_h_data()（位于OpenWRT内核文件夹子目录/net/mac80211，文件rx.c中）。

static ieee80211_rx_result debug_noinline ieee80211_rx_h_data(struct ieee80211_rx_data *rx){… rx->skb->dev = dev; dev->stats.rx_packets++; dev->stats.rx_bytes += rx->skb->len; if (local->ps_sdata && local->hw.conf.dynamic_ps_timeout > 0 && !is_multicast_ether_addr( ((struct ethhdr *)rx->skb->data)->h_dest) && (!local->scanning && !test_bit(SDATA_STATE_OFFCHANNEL, &sdata->state))) { mod_timer(&local->dynamic_ps_timer, jiffies + msecs_to_jiffies(local->hw.conf.dynamic_ps_timeout)); } ieee80211_deliver_skb(rx); return RX_QUEUED;}

8. ieee80211_deliver_skb()

/* * requires that rx->skb is a frame with ethernet header */static voidieee80211_deliver_skb(struct ieee80211_rx_data *rx){ … skb = rx->skb; … if (skb) { int align __maybe_unused;#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS /* * 'align' will only take the values 0 or 2 here * since all frames are required to be aligned * to 2-byte boundaries when being passed to * mac80211; the code here works just as well if * that isn't true, but mac80211 assumes it can * access fields as 2-byte aligned (e.g. for * compare_ether_addr) */ align = ((unsigned long)(skb->data + sizeof(struct ethhdr))) & 3; if (align) { if (WARN_ON(skb_headroom(skb) < 3)) { dev_kfree_skb(skb); skb = NULL; } else { u8 *data = skb->data; size_t len = skb_headlen(skb); skb->data -= align; memmove(skb->data, data, len); skb_set_tail_pointer(skb, len); } }#endif if (skb) { /* deliver to local stack */ skb->protocol = eth_type_trans(skb, dev); memset(skb->cb, 0, sizeof(skb->cb)); netif_receive_skb(skb); } } …}调用ieee80211_deliver_skb()（位于OpenWRT内核文件夹子目录/net/mac80211，文件rx.c中）。

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这里最核心的代码就是netif_receive_skb(skb)了，至此，数据已经接收到并发送至内核的网络子系统去处理。netif_receive_skb定义于内核文件夹Linux-3.3.8的子目录/net/core的文件dev.c中。

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