OpenWRT数据接收过程

OpenWRT数据接收过程

转自：http://www.it165.net/os/html/201404/8091.html

这里使用的是ath9k网卡驱动，硬件平台是TP-link TL-WR841N V7.1 路由器。

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）

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01.

static

void

ieee80211_tasklet_handler(unsigned

long

data)

02.

{

03.

struct
ieee80211_local *local = (struct ieee80211_local *) data;

04.

struct
sk_buff *skb;

05.

while

((skb
= skb_dequeue(&local->skb_queue)) ||

06.

(skb
= skb_dequeue(&local->skb_queue_unreliable))) {

07.

switch

(skb->pkt_type)
{

08.

case

IEEE80211_RX_MSG:

09.

/*
Clear skb->pkt_type in order to not confuse kernel

10.

*
netstack. */

11.

skb->pkt_type
=

0

;

12.

ieee80211_rx(&local->hw,
skb);

13.

break

;

14.

case

IEEE80211_TX_STATUS_MSG:

15.

...

16.

default

:

17.

...

18.

}

19.

}

20.

}

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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01.

void

ieee80211_rx(struct
ieee80211_hw *hw, struct sk_buff *skb)

02.

{

03.

struct
ieee80211_local *local = hw_to_local(hw);

04.

struct
ieee80211_rate *rate = NULL;

05.

struct
ieee80211_supported_band *sband;

06.

struct
ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);

07.

...

08.

__ieee80211_rx_handle_packet(hw,
skb);

09.

rcu_read_unlock();

10.

return

;

11.

drop:

12.

kfree_skb(skb);

13.

}

14.

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。

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01.

static

void

__ieee80211_rx_handle_packet(struct
ieee80211_hw *hw, struct sk_buff *skb)

02.

{

03.

struct
ieee80211_local *local = hw_to_local(hw);

04.

struct
ieee80211_sub_if_data *sdata;

05.

struct
ieee80211_hdr *hdr;

06.

__le16
fc;

07.

struct
ieee80211_rx_data rx;

08.

struct
ieee80211_sub_if_data *prev;

09.

struct
sta_info *sta, *tmp, *prev_sta;

10.

int

err
=

0

;

11.

...

12.

hdr
= (struct ieee80211_hdr *)skb->data;

13.

ieee80211_parse_qos(&rx);

14.

ieee80211_verify_alignment(&rx);

15.

if

(unlikely(ieee80211_is_probe_resp(hdr->frame_control)
||

16.

ieee80211_is_beacon(hdr->frame_control)))

17.

{

18.

ieee80211_scan_rx(local,
skb);

/*扫描帧信息*/

19.

}

20.

if

(ieee80211_is_data(fc))
{

21.

prev_sta
= NULL;

22.

for_each_sta_info(local,
hdr->addr2, sta, tmp) {

23.

if

(!prev_sta)
{

24.

prev_sta
= sta;

25.

continue

;

26.

}

27.

rx.sta
= prev_sta;

28.

rx.sdata
= prev_sta->sdata;

29.

ieee80211_prepare_and_rx_handle(&rx,
skb,

false

);

30.

prev_sta
= sta;

31.

}

32.

...

33.

}

34.

...

35.

out:

36.

dev_kfree_skb(skb);

37.

}

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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01.

/*

02.

*
This function returns whether or not the SKB

03.

*
was destined for RX processing or not, which,

04.

*
if consume is true, is equivalent to whether

05.

*
or not the skb was consumed.

06.

*/

07.

static

bool
ieee80211_prepare_and_rx_handle(struct ieee80211_rx_data *rx, struct sk_buff *skb, bool consume)

08.

{

09.

…

10.

ieee80211_invoke_rx_handlers(rx);

11.

return

true

;

12.

}

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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01.

static

void

ieee80211_invoke_rx_handlers(struct
ieee80211_rx_data *rx)

02.

{

03.

…

04.

ieee80211_rx_reorder_ampdu(rx,
&reorder_release);

05.

ieee80211_rx_handlers(rx,
&reorder_release);

06.

return

;

07.

rxh_next:

08.

ieee80211_rx_handlers_result(rx,
res);

09.

…

10.

}

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）。

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01.

static

void

ieee80211_rx_handlers(struct
ieee80211_rx_data *rx, struct sk_buff_head *frames)

02.

{

03.

ieee80211_rx_result
res = RX_DROP_MONITOR;

04.

struct
sk_buff *skb;

05.

#define
CALL_RXH(rxh)                     \

06.

do

{
\

07.

res
= rxh(rx);              \

08.

if

(res
!= RX_CONTINUE)    \

09.

goto

rxh_next;
\

10.

}

while

(

0

);

11.

spin_lock_bh(&rx->local->rx_path_lock);

12.

while

((skb
= __skb_dequeue(frames))) {

13.

/*

14.

*
all the other fields are valid across frames

15.

*
that belong to an aMPDU since they are on the

16.

*
same TID from the same station

17.

*/

18.

rx->skb
= skb;

19.

CALL_RXH(ieee80211_rx_h_decrypt)

20.

CALL_RXH(ieee80211_rx_h_check_more_data)

21.

CALL_RXH(ieee80211_rx_h_uapsd_and_pspoll)

22.

CALL_RXH(ieee80211_rx_h_sta_process)

23.

CALL_RXH(ieee80211_rx_h_defragment)

24.

CALL_RXH(ieee80211_rx_h_michael_mic_verify)

25.

/*
must be after MMIC verify so header is counted in MPDU mic */

26.

#ifdef
CPTCFG_MAC80211_MESH

27.

if

(ieee80211_vif_is_mesh(&rx->sdata->vif))

28.

CALL_RXH(ieee80211_rx_h_mesh_fwding);

29.

#endif

30.

CALL_RXH(ieee80211_rx_h_amsdu)

31.

CALL_RXH(ieee80211_rx_h_data)

32.

/*
special treatment -- needs the queue */

33.

res
= ieee80211_rx_h_ctrl(rx, frames);

34.

if

(res
!= RX_CONTINUE)

35.

goto

rxh_next;

36.

CALL_RXH(ieee80211_rx_h_mgmt_check)

37.

CALL_RXH(ieee80211_rx_h_action)

38.

CALL_RXH(ieee80211_rx_h_userspace_mgmt)

39.

CALL_RXH(ieee80211_rx_h_action_return)

40.

CALL_RXH(ieee80211_rx_h_mgmt)

41.

rxh_next:

42.

ieee80211_rx_handlers_result(rx,
res);

43.

#undef
CALL_RXH

44.

}

45.

spin_unlock_bh(&rx->local->rx_path_lock);

46.

}

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）。

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01.

static

ieee80211_rx_result
debug_noinline ieee80211_rx_h_data(struct ieee80211_rx_data *rx)

02.

{

03.

…

04.

rx->skb->dev
= dev;

05.

dev->stats.rx_packets++;

06.

dev->stats.rx_bytes
+= rx->skb->len;

07.

if

(local->ps_sdata
&& local->hw.conf.dynamic_ps_timeout >

0

&&

08.

!is_multicast_ether_addr(

09.

((struct
ethhdr *)rx->skb->data)->h_dest) &&

10.

(!local->scanning
&&

11.

!test_bit(SDATA_STATE_OFFCHANNEL,
&sdata->state))) {

12.

mod_timer(&local->dynamic_ps_timer,
jiffies +

13.

msecs_to_jiffies(local->hw.conf.dynamic_ps_timeout));

14.

}

15.

ieee80211_deliver_skb(rx);

16.

return

RX_QUEUED;

17.

}

8. ieee80211_deliver_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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01.

/*

02.

*
requires that rx->skb is a frame with ethernet header

03.

*/

04.

static

void

05.

ieee80211_deliver_skb(struct
ieee80211_rx_data *rx)

06.

{

07.

…

08.

skb
= rx->skb;

09.

…

10.

if

(skb)
{

11.

int

align
__maybe_unused;

12.

#ifndef
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS

13.

/*

14.

*
'align' will only take the values 0 or 2 here

15.

*
since all frames are required to be aligned

16.

*
to 2-byte boundaries when being passed to

17.

*
mac80211; the code here works just as well if

18.

*
that isn't true, but mac80211 assumes it can

19.

*
access fields as 2-byte aligned (e.g. for

20.

*
compare_ether_addr)

21.

*/

22.

align
= ((unsigned

long

)(skb->data
+ sizeof(struct ethhdr))) &

3

;

23.

if

(align)
{

24.

if

(WARN_ON(skb_headroom(skb)
<

3

))
{

25.

dev_kfree_skb(skb);

26.

skb
= NULL;

27.

}

else

{

28.

u8
*data = skb->data;

29.

size_t
len = skb_headlen(skb);

30.

skb->data
-= align;

31.

memmove(skb->data,
data, len);

32.

skb_set_tail_pointer(skb,
len);

33.

}

34.

}

35.

#endif

36.

if

(skb)
{

37.

/*
deliver to local stack */

38.

skb->protocol
= eth_type_trans(skb, dev);

39.

memset(skb->cb,

0

,
sizeof(skb->cb));

40.

netif_receive_skb(skb);

41.

}

42.

}

43.

…

44.

}

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。