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/Documentation/usb/usbmon.txt

https://bitbucket.org/evzijst/gittest
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  1* Introduction
  2
  3The name "usbmon" in lowercase refers to a facility in kernel which is
  4used to collect traces of I/O on the USB bus. This function is analogous
  5to a packet socket used by network monitoring tools such as tcpdump(1)
  6or Ethereal. Similarly, it is expected that a tool such as usbdump or
  7USBMon (with uppercase letters) is used to examine raw traces produced
  8by usbmon.
  9
 10The usbmon reports requests made by peripheral-specific drivers to Host
 11Controller Drivers (HCD). So, if HCD is buggy, the traces reported by
 12usbmon may not correspond to bus transactions precisely. This is the same
 13situation as with tcpdump.
 14
 15* How to use usbmon to collect raw text traces
 16
 17Unlike the packet socket, usbmon has an interface which provides traces
 18in a text format. This is used for two purposes. First, it serves as a
 19common trace exchange format for tools while most sophisticated formats
 20are finalized. Second, humans can read it in case tools are not available.
 21
 22To collect a raw text trace, execute following steps.
 23
 241. Prepare
 25
 26Mount debugfs (it has to be enabled in your kernel configuration), and
 27load the usbmon module (if built as module). The second step is skipped
 28if usbmon is built into the kernel.
 29
 30# mount -t debugfs none_debugs /sys/kernel/debug
 31# modprobe usbmon
 32
 33Verify that bus sockets are present.
 34
 35[root@lembas zaitcev]# ls /sys/kernel/debug/usbmon
 361s  1t  2s  2t  3s  3t  4s  4t
 37[root@lembas zaitcev]#
 38
 39# ls /sys/kernel
 40
 412. Find which bus connects to the desired device
 42
 43Run "cat /proc/bus/usb/devices", and find the T-line which corresponds to
 44the device. Usually you do it by looking for the vendor string. If you have
 45many similar devices, unplug one and compare two /proc/bus/usb/devices outputs.
 46The T-line will have a bus number. Example:
 47
 48T:  Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=12  MxCh= 0
 49D:  Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
 50P:  Vendor=0557 ProdID=2004 Rev= 1.00
 51S:  Manufacturer=ATEN
 52S:  Product=UC100KM V2.00
 53
 54Bus=03 means it's bus 3.
 55
 563. Start 'cat'
 57
 58# cat /sys/kernel/debug/usbmon/3t > /tmp/1.mon.out
 59
 60This process will be reading until killed. Naturally, the output can be
 61redirected to a desirable location. This is preferred, because it is going
 62to be quite long.
 63
 644. Perform the desired operation on the USB bus
 65
 66This is where you do something that creates the traffic: plug in a flash key,
 67copy files, control a webcam, etc.
 68
 695. Kill cat
 70
 71Usually it's done with a keyboard interrupt (Control-C).
 72
 73At this point the output file (/tmp/1.mon.out in this example) can be saved,
 74sent by e-mail, or inspected with a text editor. In the last case make sure
 75that the file size is not excessive for your favourite editor.
 76
 77* Raw text data format
 78
 79The '0t' type data consists of a stream of events, such as URB submission,
 80URB callback, submission error. Every event is a text line, which consists
 81of whitespace separated words. The number of position of words may depend
 82on the event type, but there is a set of words, common for all types.
 83
 84Here is the list of words, from left to right:
 85- URB Tag. This is used to identify URBs is normally a kernel mode address
 86 of the URB structure in hexadecimal.
 87- Timestamp in microseconds, a decimal number. The timestamp's resolution
 88  depends on available clock, and so it can be much worse than a microsecond
 89  (if the implementation uses jiffies, for example).
 90- Event Type. This type refers to the format of the event, not URB type.
 91  Available types are: S - submission, C - callback, E - submission error.
 92- "Pipe". The pipe concept is deprecated. This is a composite word, used to
 93  be derived from information in pipes. It consists of three fields, separated
 94  by colons: URB type and direction, Device address, Endpoint number.
 95  Type and direction are encoded with two bytes in the following manner:
 96    Ci Co   Control input and output
 97    Zi Zo   Isochronous input and output
 98    Ii Io   Interrupt input and output
 99    Bi Bo   Bulk input and output
100  Device address and Endpoint number are decimal numbers with leading zeroes
101  or 3 and 2 positions, correspondingly.
102- URB Status. This field makes no sense for submissions, but is present
103  to help scripts with parsing. In error case, it contains the error code.
104- Data Length. This is the actual length in the URB.
105- Data tag. The usbmon may not always capture data, even if length is nonzero.
106  Only if tag is '=', the data words are present.
107- Data words follow, in big endian hexadecimal format. Notice that they are
108  not machine words, but really just a byte stream split into words to make
109  it easier to read. Thus, the last word may contain from one to four bytes.
110  The length of collected data is limited and can be less than the data length
111  report in Data Length word.
112
113Here is an example of code to read the data stream in a well known programming
114language:
115
116class ParsedLine {
117	int data_len;		/* Available length of data */
118	byte data[];
119
120	void parseData(StringTokenizer st) {
121		int availwords = st.countTokens();
122		data = new byte[availwords * 4];
123		data_len = 0;
124		while (st.hasMoreTokens()) {
125			String data_str = st.nextToken();
126			int len = data_str.length() / 2;
127			int i;
128			for (i = 0; i < len; i++) {
129				data[data_len] = Byte.parseByte(
130				    data_str.substring(i*2, i*2 + 2),
131				    16);
132				data_len++;
133			}
134		}
135	}
136}
137
138This format is obviously deficient. For example, the setup packet for control
139transfers is not delivered. This will change in the future.
140
141Examples:
142
143An input control transfer to get a port status:
144
145d74ff9a0 2640288196 S Ci:001:00 -115 4 <
146d74ff9a0 2640288202 C Ci:001:00 0 4 = 01010100
147
148An output bulk transfer to send a SCSI command 0x5E in a 31-byte Bulk wrapper
149to a storage device at address 5:
150
151dd65f0e8 4128379752 S Bo:005:02 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000
152dd65f0e8 4128379808 C Bo:005:02 0 31 >
153
154* Raw binary format and API
155
156TBD