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1、配置内核使能usb monitor：

make menuconfig
Device Drivers -->
USB Support -->
USB Monitor --> Select * not M
2、build kernel
sudo insmod /lib/modules/3.2.1/kernel/drivers/usb/mon/usbmon.ko

3、启动内核后执行
#mount -t debugfs none_debugs /sys/kernel/debug

检查是否存在目录 /sys/kernel/debug/usb/usbmon
#ls /sys/kernel/debug/usb/usbmon

                   0s 0u 1s 1t 1u 2s 2t 2u 3s 3t 3u

                  # cat /sys/kernel/debug/usb/devices 确定你要监视的usb设备所在总线号和设备号
                   # 选择包含有 : Vendor=148f ProdID=5370 Rev= 1.01 的段落
# as follows:
# T: Bus=01Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=480 MxCh= 0
# D: Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs= 1
# P: Vendor=148f ProdID=5370 Rev= 1.01
# S: Manufacturer=Ralink
# S: Product=802.11 n WLAN
# S: SerialNumber=1.0
# C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=450mA
# I:* If#= 0 Alt= 0 #EPs= 5 Cls=ff(vend.) Sub=ff Prot=ff Driver=rtusbSTA
# E: Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
# E: Ad=01(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
# E: Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
# E: Ad=03(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
# E: Ad=04(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
#   可以从第一行看到 Bus= 01,设备号是2

4、保存 usb raw packet ，如果总线号是1，则是1u，如果总线号是2，则是2u，依次类推。特殊情况是0u表示监听所有总线
if (Bus == 01)
sudo cat /sys/kernel/debug/usb/usbmon/1u > ./rt5370-UsbMon.txt
else if (Bus == 02)
sudo cat /sys/kernel/debug/usb/usbmon/2u > ./rt5370-UsbMon.txt

2 抓的usb包的格式解析

The usbmon reports requests made by peripheral-specific drivers to Host
Controller Drivers (HCD). So, if HCD is buggy, the traces reported by
usbmon may not correspond to bus transactions precisely. This is the same
situation as with tcpdump.

上面的基本说明了usbmon主要的工作原理，他会把usb host drivers发送到hcd的所有请求（usb_submit_urb）和请求的回调内容（即改请求对应的回调函数：urb->complete）都报告出来。

Any text format data consists of a stream of events, such as URB submission（S）,
URB callback（C）, submission error（E）. Every event is a text line, which consists
of whitespace separated words. The number or position of words may depend
on the event type, but there is a set of words, common for all types.

所以这里的URB submission即是对应usb host drivers中的usb_submit_urb(urb, mem_flags)

而URB callback即使对应urb的回掉函数：urb->complete

所以我们会看到even type为S的和紧邻的event type为C的事件，他们对应的URB tag都是一样的

因为他们都是针对同一个URB而言的。

先给出三个列子：

eea76f80 3474782286 S Ii:1:003:3 -115:128 16 <
edda2b80 3474786256 C Ii:1:006:1 0:1 16 = 2fff0180 d6ef206e 1401020c 015aab73
e11c9280 3500399358 S Co:1:006:0 s 20 00 0000 0000 0007 7 = 370c0447 00401f
e11c9280 3500399866 C Co:1:006:0 0 7 >

Here is the list of words, from left to right:

- URB Tag. This is used to identify URBs, and is normally an in-kernel address
of the URB structure in hexadecimal, but can be a sequence number or any
other unique string, within reason.

一般就是在usb host driver中分配的urb的内核地址，一般通过如下函数来分配：

urb = usb_alloc_urb(0, mem_flags);

由于一个urb对应一个端口，所以同一个端口他们的urb tag都是一样的。
002e2002999116296 C Ci:1:008:0 0 4 = 8d2b0000

Timestampin microseconds, a decimal number. The timestamp's resolution
depends on available clock, and so it can be much worse than a microsecond
(if the implementation uses jiffies, for example).
e002e200 2999116296Ci:1:008:0 0 4 = 8d2b0000

注意单位是微秒。

- Event Type. This type refers to the format of the event, not URB type.
Available types are:S - submission, C - callback, E - submission error.
e002e200 2999116296 C Ci:1:008:0 0 4 = 8d2b0000

表示的意思是：usb host drivers通过usb_submit_urb函数向linuxusb core提交了一个urb传输请求，我们知道所有的usb传输，都是host端主动发起的，所以必须要有host drivers主动发出submit urb的动作

- "Address" word (formerly a "pipe"). It consists of four fields, separated by
colons: URB type and direction, Bus number, Device address, Endpoint number.
Type and direction are encoded with two bytes in the following manner:
  Ci Co   Control input and output
  Zi Zo   Isochronous input and output
  Ii Io   Interrupt input and output
  Bi Bo   Bulk input and output
Bus number, Device address, and Endpoint are decimal numbers, but they may
have leading zeros, for the sake of human readers.

所以地址字段的格式是如下：

URB type and direction：Bus number：Device address：Endpoint number

如下列子：
e002e200 2999116296 C Ci:1:008:0 0 4 = 8d2b0000

意思是：控制传输输入，总线号为1，设备地址为008，由于所有的控制传输都是在endpoint 0上的，所以最后的端口自然也是0了。

这里需要注意，由于我们的这个抓包命令，只能指定是抓哪个总线上，但同一个总线通常会有很多usb设备的，如果我们只是关注特定的某个usb设备的话，我自己就需要留意设备地址字段，通过这个字段，我们就可以区分这个传输是不是我们要监听的设备发送出来的。

例如下面一段usb sniffer log：

edda2b80 3500379613 C Ii:1:006:1 0:1 8 = 0e06010d 08004700
edda2b80 3500394156 S Ii:1:006:1-115:1 16 <
eea76f80 3500394226 C Ii:1:003:3 0:128 16 = a12a0000 01000800 00e1f505 00e1f505
eea76f80 3500394236 S Ii:1:003:3 -115:128 16 <

同样都是usb总线1下面的，由于一个usb总线就对应一个usb host controller，但一个设备地址是006，另一个则是003，前者对应的是usb bluetooth dongle的中断传输，而后者则是usb鼠标的中断传输，他们接在同一个总线的usb hub下面。我们真正需要监听只是usb bluetooth dongle，所以就可以不受usb鼠标的干扰。

- URB Status word. This is either a letter, or several numbers separated
by colons: URB status, interval, start frame, and error count. Unlike the
"address" word, all fields save the status are optional. Interval is printed
only for interrupt and isochronous URBs. Start frame is printed only for
isochronous URBs. Error count is printed only for isochronous callback
events.
这里的意思就是，urb的状态字，有两种可能，一种是“字母”；一种是“数字”，如果是前者则一般就是字母“s”，表示一个控制传输，而如果是数字，他们的格式则分两种情况：

如果是中断传输，格式如下： URB status：interval，注意状态字段只对C类型的事件有意义，对S类型的事件没有意思。

如果是同步传输,格式如下：URB status：interval：{start frame}：{error count}

The status field is a decimal number, sometimes negative, which represents
a "status" field of the URB. This field makes no sense for submissions, but
is present anyway to help scripts with parsing. When an error occurs, the
field contains the error code.
e002e200 2999116296 C Ci:1:008:0 0 4 = 8d2b0000

状态域：status就是struct urb结构体中的status字段，该字段直接说明当前的usb请求是否成功执行。所以只有在回调的时候才有意思。

In case of a submission of a Control packet, this field contains a Setup Tag
instead of an group of numbers. It is easy to tell whether the Setup Tag is
present because it is never a number. Thus if scripts find a set of numbers
in this word, they proceed to read Data Length (except for isochronous URBs).
If they find something else, like a letter, they read the setup packet before
reading the Data Length or isochronous descriptors.
e002e200 2999116113 S Ci:1:008:0 s c0 07 0000 1134 0004 4 <

字母“s”是控制传输的标志

- Setup packet, if present, consists of 5 words: one of each for bmRequestType,
bRequest, wValue, wIndex, wLength, as specified by the USB Specification 2.0.
These words are safe to decode if Setup Tag was 's'. Otherwise, the setup
packet was present, but not captured, and the fields contain filler.

即控制传输包的格式如下：

bmRequestType（请求类型）：bRequest（请求号）：wValue：wIndex（下标）：wLength（数据字段的长度，如果为0，说明没有数据段）

e11c9280 3500399358 S Co:1:006:0 s 20 00 0000 0000 0007 7 = 370c0447 00401f

e11c9280 3500399866 C Co:1:006:0 0 7 > //表示上面的控制传输请求成功，并且实际传输了7个btye的数据，仅表示状态，不对应具体的控制传输阶段

20 00 0000 0000 0007对应控制传输的setup阶段， 370c0447 00401f对应控制传输的数据阶段（OUT传输），数据长度是7个字节

- Number of isochronous frame descriptors and descriptors themselves.
If an Isochronous transfer event has a set of descriptors, a total number
of them in an URB is printed first, then a word per descriptor, up to a
total of 5. The word consists of 3 colon-separated decimal numbers for
status, offset, and length respectively. For submissions, initial length
is reported. For callbacks, actual length is reported.

- Data Length. For submissions, this is the requested length. For callbacks,
this is the actual length.
e002e200 2999116296 C Ci:1:008:0 0 4 = 8d2b0000

又如下：

edda2b80 3500272851 S Ii:1:006:1 -115:1 16 <
edda2b80 3500273622 C Ii:1:006:1 0:1 7 = 13050147 000100

第一句是发起一个请求长度为16字节的usb中断传输请求，该字段一般在端点描述符中会说明该管道所支持的最大数据包大小

第二句是该中断传输请求实际返回的数据则只有7个字节，即对应urb->actual_length字段

以上两句对应一个中断IN传输

- Data tag. The usbmon may not always capture data, even if length is nonzero.
The data words are present only if this tag is '='.
e002e200 2999116296 C Ci:1:008:0 0 4 =8d2b0000

data tag就是“=”，表示有数据段，“=”号后面就是具体的数据内容

- Data words follow, in big endian hexadecimal format. Notice that they are
not machine words, but really just a byte stream split into words to make
it easier to read. Thus, the last word may contain from one to four bytes.
The length of collected data is limited and can be less than the data length
reported in the Data Length word. In the case of an Isochronous input (Zi)
completion where the received data is sparse in the buffer, the length of
the collected data can be greater than the Data Length value (because Data
Length counts only the bytes that were received whereas the Data words
contain the entire transfer buffer).
e002e200 2999116296 C Ci:1:008:0 0 4 = 8d2b0000

Examples:
An input control transfer to get a port status.
d5ea89a0 3575914555 S Ci:1:001:0 s a3 00 0000 0003 00044<

“ a3 00 0000 0003 0004”对应控制传输的setup阶段，“4”对应控制传输的数据阶段长度
5ea89a0 3575914560 C Ci:1:001:0 0 4 = 01050000
对应控制传输的数据阶段的data IN传输，” 01050000“即为数据，为4byte长度

An output bulk transfer to send a SCSI command 0x28 (READ_10) in a 31-byte
Bulk wrapper to a storage device at address 5:

dd65f0e8 4128379752 S Bo:1:005:2 -115 31 = 55534243 ad000000 00800000 80010a28 20000000 20000040 00000000 000000
dd65f0e8 4128379808 C Bo:1:005:2 0 31 > //指示这个bulk传输请求时成功的，并且实际也传输了31个byte的数据。

3 USB Sniffing with tcpdump

usbmon is a facility in kernel which is used to collect traces of I/O on the USB bus. usbmon collects raw text/binary which are not easily human-readable. Here, the idea is to use Wireshark as frontend to produces a human-readable representation of these data. However Wireshark does not support usbmon raw data as is, so we have to parse these data in the pcap format. tcpdump is a good candidate to capture USB data from usbmon and generate pcap traces

前提条件，是需要最新的tcpdump工具才行，有编译好的，可以直接download下来push到板子上就可以使用。也有可以自己手动来编译的。这里就不详细来说了。

步骤：

mount -t debugfs none_debugs /sys/kernel/debug
cat /sys/kernel/debug/usb/devices 确定usb的总线号
tcpdump -D

1.eth0
2.usbmon1 (USB bus number 1)
3.usbmon2 (USB bus number 2)
4.usbmon3 (USB bus number 3)
5.any (Pseudo-device that captures on all interfaces)
6.lo

有以上红色部分输出，说明你的tcpdump已经安装下，可以正常使用