Tethering技術在移動平臺上已經(jīng)運用的越來越廣泛了。它能夠把移動設備當做一個接入點，其它的設備能夠通過Wi-Fi。USB或是Bluetooth等方式連接到此移動設備。在Android中能夠將Wifi設為AP模式作為WLAN接入點。從而與其它設備共享Android的互聯(lián)網(wǎng)連接。Android成為接入點后。就無法通過WLAN連接使用Android的應用程序訪問互聯(lián)網(wǎng)，但能夠通過其它方式如以太網(wǎng)或移動網(wǎng)絡訪問互聯(lián)網(wǎng)。

此時以太網(wǎng)或移動網(wǎng)絡在網(wǎng)絡共享（Tethering）中是作為upstream的角色。

?

近期在Atmel的SAMA5D3-EK開發(fā)板上調試Wifi模塊。須要在Android下實現(xiàn)Tethering，通過Wi-Fi的AP模式。將網(wǎng)絡連接共享給其他設備。

?

開發(fā)板上一個有線網(wǎng)卡(eth0)，一個無線網(wǎng)卡(wlan0)。eth0連接到外網(wǎng)，wlan0作為AP共享給其它設備比方Android手機，使得Android手機能夠通過開發(fā)板連接到外網(wǎng)。

?

硬件平臺：Atmel SAMA5

軟件平臺：Linux 3.10 +Android 4.4

Wifi模組：RTL8723AU(USB接口)

?

由于使用的內核是廠商基于主線內核開發(fā)的，盡管主線內核中加入了Android的基本支持，但并不全然。

在做Android移植時，假設發(fā)現(xiàn)Android上層的某些功能缺乏內核的支持，能夠依據(jù)Google維護的AndroidLinux內核將對應的更改應用到廠商Linux內核中，在前文《Android KitKat 4.4平臺開發(fā)-加入USBADB和MTP功能支持》中就是使用的這樣的方法。

?

整個Wifi移植過程，Wifi模組廠商Realtek給出了具體的過程。但內容僅僅涉及Wifi驅動及Android部分。使用哪個Linux內核以及內核怎樣配置須要我們自己決定。

?

依照Realtek提供的移植文檔進行AndroidWifi的移植，在測試Wifi 網(wǎng)絡共享功能時出現(xiàn)例如以下問題：

在“設置”程序“網(wǎng)絡共享與便攜式熱點”中，打開“便攜式Wi-Fi熱點”。并沒有真正開啟Wifi熱點。而是對應單選框不斷關開，如此重復。

?

對于在測試Android功能時出現(xiàn)的異常情況。一般在log中會存在對應的錯誤信息，盡管并非絕對準確，但調試時應該考慮先分析log信息，嘗試從中定位導致異常發(fā)生的代碼位置。

經(jīng)過一番分析猜測。例如以下高亮顯示的log信息非常有可能是誘發(fā)異常發(fā)生的關鍵代碼點。

V/NatController(972): enableNat(intIface=<wlan0>, extIface=<eth0>)

V/NatController(972): runCmd(/system/bin/iptables -t nat -A natctrl_nat_POSTROUTING -o eth0 -jMASQUERADE) res=0

V/NatController(972): runCmd(/system/bin/iptables -A natctrl_FORWARD -i eth0 -o wlan0 -m state--state ESTABLISHED,RELATED -g natctrl_tether_counters) res=0

D/dalvikvm(1339): GC_CONCURRENT freed 373K, 54% free 6723K/14460K, paused 44ms+14ms, total219ms

V/NatController(972): runCmd(/system/bin/iptables -A natctrl_FORWARD -i wlan0 -o eth0 -m state--state INVALID -j DROP) res=0

V/NatController(972): runCmd(/system/bin/iptables -A natctrl_FORWARD -i wlan0 -o eth0 -gnatctrl_tether_counters) res=0

V/NatController( 972): runCmd(/system/bin/iptables-A natctrl_tether_counters -i wlan0 -o eth0 -m quota2 --name wlan0_eth0 --grow-j RETURN) res=1

V/NatController(972): runCmd(/system/bin/iptables -D natctrl_FORWARD -i wlan0 -o eth0 -m state--state INVALID -j DROP) res=0

V/NatController(972): runCmd(/system/bin/iptables -D natctrl_FORWARD -i eth0 -o wlan0 -m state--state ESTABLISHED,RELATED -g natctrl_tether_counters) res=0

E/NatController( 972): Error setting forward rules

V/NatController(972): runCmd(/system/bin/iptables -F natctrl_FORWARD) res=0

V/NatController(972): runCmd(/system/bin/iptables -A natctrl_FORWARD -j DROP) res=0

http://androidxref.com/4.4.2_r1/xref/system/netd/NatController.cpp#294

256int NatController::setTetherCountingRules(bool add, const char *intIface, const char *extIface) {
257
258??? /* We only ever add tethering quota rules so thatthey stick. */
259??? if (!add) {
260??????? return 0;
261??? }
262??? char *quota_name, *proc_path;
263??? int quota_fd;
264??? asprintf(&quota_name, "%s_%s", intIface, extIface);
265
266??? asprintf(&proc_path, "/proc/net/xt_quota/%s", quota_name);
267??? quota_fd = open(proc_path, O_RDONLY);
268??? if (quota_fd >= 0) {
269??????? /* quota for iface pair already exists*/
270??????? free(proc_path);
271??????? free(quota_name);
272??????? return 0;
273??? }
274??? close(quota_fd);
275??? free(proc_path);
276
277??? const char *cmd2b[] = {
278??????????? IPTABLES_PATH,
279??????????? "-A",
280??????????? LOCAL_TETHER_COUNTERS_CHAIN,
281??????????? "-i",
282??????????? intIface,
283??????????? "-o",
284??????????? extIface,
285??????????? "-m",
286??????????? "quota2",
287??????????? "--name",
288??????????? quota_name,
289??????????? "--grow",
290??????????? "-j",
291????????? "RETURN"
292??? };
293
294??? if (runCmd(ARRAY_SIZE(cmd2b), cmd2b) && add) {
295??????? free(quota_name);
296??????? return -1;
297??? }
298??? free(quota_name);
299
300??? asprintf(&quota_name, "%s_%s", extIface, intIface);
301??? asprintf(&proc_path, "/proc/net/xt_quota/%s", quota_name);
302??? quota_fd = open(proc_path, O_RDONLY);
303??? if (quota_fd >= 0) {
304??????? /* quota for iface pair already exists*/
305??????? free(proc_path);
306??????? free(quota_name);
307??????? return 0;
308??? }
309??? close(quota_fd);
310??? free(proc_path);
311

?

分析這個函數(shù)NatController::setTetherCountingRules及log信息，判斷出異常發(fā)生的原因是運行命令

/system/bin/iptables -A natctrl_tether_counters -i wlan0 -o eth0 -mquota2 --name wlan0_eth0 --grow -j 失敗。

并且還涉及到路徑/proc/net/xt_quota/，但當前系統(tǒng)下并不存在這個路徑。

由此判斷應該是內核缺乏與quota2或xt_quota相關的支持。

?

找到問題的可能原因，接下來就是驗證了。比較Android Linux內核、廠商Linux內核以及主線Linux內核網(wǎng)絡部分的差異。發(fā)現(xiàn)Android Linux內核在主線Linux內核基礎上添加了quota2的支持。

涉及四次提交

$git log --name-only net/netfilter/xt_quota2.cinclude/linux/netfilter/xt_quota2.h net/netfilter/Kconfignet/netfilter/Makefile

commit7d89969ad270d4c535e33830188806233bf35442

Author:Greg Hackmann <ghackmann@google.com>

Date:Mon Feb 24 09:39:46 2014 -0800

? ? netfilter: xt_qtaguid: 64-bit warning fixes

? ? Change-Id:I2adc517c0c51050ed601992fa0ea4de8f1449414

? ? Signed-off-by: Greg Hackmann<ghackmann@google.com>

net/netfilter/xt_quota2.c

?

commit73570fe76d3b47e669558f06f1a18e0f02dff606

Author:Arve Hj?nnev?g <arve@android.com>

Date:Mon May 13 20:42:46 2013 -0700

? ? netfilter: xt_quota2: 3.10 fixes.

? ? - Stop using obsolete create_proc_entry api.

? ? - Use proc_set_user instead of directlyaccessing the private structure.

? ? Signed-off-by: Arve Hj?nnev?g<arve@android.com>

net/netfilter/xt_quota2.c

?

commitea34f99edb73b67ef0a99d304887c64febd4c878

Author:JP Abgrall <jpa@google.com>

Date:Tue Jul 12 12:02:59 2011 -0700

? ? netfilter: fixup the quota2, and enable.

? ? The xt_quota2 came from

? ? ? http://sourceforge.net/projects/xtables-addons/develop

? ? It needed tweaking for it to compile withinthe kernel tree.

? ? Fixed kmalloc() and create_proc_entry()invocations within

? ? ?a non-interruptible context.

? ? Removed useless copying of current quotaback to the iptable's

? ? struct matchinfo:

? ? ? - those are per CPU: they will changerandomly based on which

? ? ? ? cpu gets to update the value.

? ? ? - they prevent matching a rule: e.g.

? ? ? ? ? -A chain -m quota2 --name q1 --quota 123

? ? ? ? ?can't be followed by

? ? ? ? ? -D chain -m quota2 --name q1 --quota 123

? ? ? ? as the 123 will be compared to the structmatchinfo's quota member.

? ? Use the NETLINK NETLINK_NFLOG family to loga single message

? ? when the quota limit is reached.

? ? It uses the same packet type as ipt_ULOG,but

? ? ?- never copies skb data,

? ? ?- uses 112 as the event number (ULOG's +1)

? ? It doesn't log if the module param"event_num" is 0.

? ? Change-Id:I021d3b743db3b22158cc49acb5c94d905b501492

? ? Signed-off-by: JP Abgrall<jpa@google.com>

net/netfilter/Kconfig

net/netfilter/Makefile

net/netfilter/xt_quota2.c

?

commit3db08b39ea752748744e9c7733ce9ef54bed9f3b

Author:JP Abgrall <jpa@google.com>

Date:Tue Jun 21 11:14:49 2011 -0700

? ? netfilter: adding the original quota2 fromxtables-addons

? ? The original xt_quota in the kernel is plainbroken:

? ? ? - counts quota at a per CPU level

? ? ? ? (was written back when ubiquitous SMP wasjust a dream)

? ? ? - provides no way to count across IPV4/IPV6.

? ? This patch is the original unaltered codefrom:

? ? ? http://sourceforge.net/projects/xtables-addons

? ? ? at commite84391ce665cef046967f796dd91026851d6bbf3

? ? Change-Id:I19d49858840effee9ecf6cff03c23b45a97efdeb

? ? Signed-off-by: JP Abgrall<jpa@google.com>

include/linux/netfilter/xt_quota2.h

net/netfilter/xt_quota2.c

?

提取quota2相關的commit，制作補丁

$ git format-patch -n4 net/netfilter/xt_quota2.c include/linux/netfilter/xt_quota2.hnet/netfilter/Kconfig net/netfilter/Makefile 0001-netfilter-adding-the-original-quota2-from-xtables-ad.patch 0002-netfilter-fixup-the-quota2-and-enable.patch 0003-netfilter-xt_quota2-3.10-fixes.patch 0004-netfilter-xt_qtaguid-64-bit-warning-fixes.patch ?

將這些補丁應用到廠商Linux內核 （git am命令）

?

在內核配置中添加quota2支持

commit4e6bf851ffd340f83062d053a6a20d358def121e

Author:Max Liao <liaops@embedinfo.com>

Date:Mon Jun 16 06:08:25 2014 -0400

? ? ARM: at91/SAMA5: android_ubifs_defconfig:add netfilter quota2 support for sama5d3 and sama5d4

? ? Signed-off-by: Max Liao<liaops@embedinfo.com>

diff--git a/arch/arm/configs/sama5_android_ubifs_defconfigb/arch/arm/configs/sama5_android_ubifs_defconfig

index9881f7d..48c68a1 100644

---a/arch/arm/configs/sama5_android_ubifs_defconfig

+++b/arch/arm/configs/sama5_android_ubifs_defconfig

@@-623,6 +623,7 @@ CONFIG_NETFILTER_XT_MATCH_OSF=y

?CONFIG_NETFILTER_XT_MATCH_OWNER=y

?CONFIG_NETFILTER_XT_MATCH_PKTTYPE=y

?CONFIG_NETFILTER_XT_MATCH_QUOTA=y

+CONFIG_NETFILTER_XT_MATCH_QUOTA2=y

?CONFIG_NETFILTER_XT_MATCH_RATEEST=y

?CONFIG_NETFILTER_XT_MATCH_REALM=y

?CONFIG_NETFILTER_XT_MATCH_RECENT=y

?

編譯內核。

?

測試Wifi 網(wǎng)絡共享功能，之前的異常現(xiàn)象消失，功能測試正常，這說明之前的推導推測是正確的。異常的原因的確是內核缺乏netfilter quota2支持。

轉載于:https://www.cnblogs.com/yxwkf/p/4606708.html

總結

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