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Linus Torvalds1da177e2005-04-16 15:20:36 -07001* 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
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -070032#
Linus Torvalds1da177e2005-04-16 15:20:36 -070033
34Verify that bus sockets are present.
35
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -070036# ls /sys/kernel/debug/usbmon
Linus Torvalds1da177e2005-04-16 15:20:36 -0700371s 1t 2s 2t 3s 3t 4s 4t
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -070038#
Linus Torvalds1da177e2005-04-16 15:20:36 -070039
402. Find which bus connects to the desired device
41
42Run "cat /proc/bus/usb/devices", and find the T-line which corresponds to
43the device. Usually you do it by looking for the vendor string. If you have
44many similar devices, unplug one and compare two /proc/bus/usb/devices outputs.
45The T-line will have a bus number. Example:
46
47T: Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 0
48D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
49P: Vendor=0557 ProdID=2004 Rev= 1.00
50S: Manufacturer=ATEN
51S: Product=UC100KM V2.00
52
53Bus=03 means it's bus 3.
54
553. Start 'cat'
56
57# cat /sys/kernel/debug/usbmon/3t > /tmp/1.mon.out
58
59This process will be reading until killed. Naturally, the output can be
60redirected to a desirable location. This is preferred, because it is going
61to be quite long.
62
634. Perform the desired operation on the USB bus
64
65This is where you do something that creates the traffic: plug in a flash key,
66copy files, control a webcam, etc.
67
685. Kill cat
69
70Usually it's done with a keyboard interrupt (Control-C).
71
72At this point the output file (/tmp/1.mon.out in this example) can be saved,
73sent by e-mail, or inspected with a text editor. In the last case make sure
74that the file size is not excessive for your favourite editor.
75
76* Raw text data format
77
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -070078The '1t' type data consists of a stream of events, such as URB submission,
Linus Torvalds1da177e2005-04-16 15:20:36 -070079URB callback, submission error. Every event is a text line, which consists
80of whitespace separated words. The number of position of words may depend
81on the event type, but there is a set of words, common for all types.
82
83Here is the list of words, from left to right:
84- URB Tag. This is used to identify URBs is normally a kernel mode address
85 of the URB structure in hexadecimal.
86- Timestamp in microseconds, a decimal number. The timestamp's resolution
87 depends on available clock, and so it can be much worse than a microsecond
88 (if the implementation uses jiffies, for example).
89- Event Type. This type refers to the format of the event, not URB type.
90 Available types are: S - submission, C - callback, E - submission error.
91- "Pipe". The pipe concept is deprecated. This is a composite word, used to
92 be derived from information in pipes. It consists of three fields, separated
93 by colons: URB type and direction, Device address, Endpoint number.
94 Type and direction are encoded with two bytes in the following manner:
95 Ci Co Control input and output
96 Zi Zo Isochronous input and output
97 Ii Io Interrupt input and output
98 Bi Bo Bulk input and output
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -070099 Device address and Endpoint number are 3-digit and 2-digit (respectively)
100 decimal numbers, with leading zeroes.
101- URB Status. In most cases, this field contains a number, sometimes negative,
102 which represents a "status" field of the URB. This field makes no sense for
103 submissions, but is present anyway to help scripts with parsing. When an
104 error occurs, the field contains the error code. In case of a submission of
105 a Control packet, this field contains a Setup Tag instead of an error code.
106 It is easy to tell whether the Setup Tag is present because it is never a
107 number. Thus if scripts find a number in this field, they proceed to read
108 Data Length. If they find something else, like a letter, they read the setup
109 packet before reading the Data Length.
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700110- Setup packet, if present, consists of 5 words: one of each for bmRequestType,
111 bRequest, wValue, wIndex, wLength, as specified by the USB Specification 2.0.
112 These words are safe to decode if Setup Tag was 's'. Otherwise, the setup
113 packet was present, but not captured, and the fields contain filler.
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -0700114- Data Length. For submissions, this is the requested length. For callbacks,
115 this is the actual length.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700116- Data tag. The usbmon may not always capture data, even if length is nonzero.
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -0700117 The data words are present only if this tag is '='.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700118- Data words follow, in big endian hexadecimal format. Notice that they are
119 not machine words, but really just a byte stream split into words to make
120 it easier to read. Thus, the last word may contain from one to four bytes.
121 The length of collected data is limited and can be less than the data length
122 report in Data Length word.
123
124Here is an example of code to read the data stream in a well known programming
125language:
126
127class ParsedLine {
128 int data_len; /* Available length of data */
129 byte data[];
130
131 void parseData(StringTokenizer st) {
132 int availwords = st.countTokens();
133 data = new byte[availwords * 4];
134 data_len = 0;
135 while (st.hasMoreTokens()) {
136 String data_str = st.nextToken();
137 int len = data_str.length() / 2;
138 int i;
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700139 int b; // byte is signed, apparently?! XXX
Linus Torvalds1da177e2005-04-16 15:20:36 -0700140 for (i = 0; i < len; i++) {
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700141 // data[data_len] = Byte.parseByte(
142 // data_str.substring(i*2, i*2 + 2),
143 // 16);
144 b = Integer.parseInt(
145 data_str.substring(i*2, i*2 + 2),
146 16);
147 if (b >= 128)
148 b *= -1;
149 data[data_len] = (byte) b;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700150 data_len++;
151 }
152 }
153 }
154}
155
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700156This format may be changed in the future.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700157
158Examples:
159
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700160An input control transfer to get a port status.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700161
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700162d5ea89a0 3575914555 S Ci:001:00 s a3 00 0000 0003 0004 4 <
163d5ea89a0 3575914560 C Ci:001:00 0 4 = 01050000
Linus Torvalds1da177e2005-04-16 15:20:36 -0700164
165An output bulk transfer to send a SCSI command 0x5E in a 31-byte Bulk wrapper
166to a storage device at address 5:
167
168dd65f0e8 4128379752 S Bo:005:02 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000
169dd65f0e8 4128379808 C Bo:005:02 0 31 >
170
171* Raw binary format and API
172
173TBD