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1da177e4 LT |
1 | * Introduction |
2 | ||
3 | The name "usbmon" in lowercase refers to a facility in kernel which is | |
4 | used to collect traces of I/O on the USB bus. This function is analogous | |
5 | to a packet socket used by network monitoring tools such as tcpdump(1) | |
6 | or Ethereal. Similarly, it is expected that a tool such as usbdump or | |
7 | USBMon (with uppercase letters) is used to examine raw traces produced | |
8 | by usbmon. | |
9 | ||
10 | The usbmon reports requests made by peripheral-specific drivers to Host | |
11 | Controller Drivers (HCD). So, if HCD is buggy, the traces reported by | |
12 | usbmon may not correspond to bus transactions precisely. This is the same | |
13 | situation as with tcpdump. | |
14 | ||
15 | * How to use usbmon to collect raw text traces | |
16 | ||
17 | Unlike the packet socket, usbmon has an interface which provides traces | |
18 | in a text format. This is used for two purposes. First, it serves as a | |
19 | common trace exchange format for tools while most sophisticated formats | |
20 | are finalized. Second, humans can read it in case tools are not available. | |
21 | ||
22 | To collect a raw text trace, execute following steps. | |
23 | ||
24 | 1. Prepare | |
25 | ||
26 | Mount debugfs (it has to be enabled in your kernel configuration), and | |
27 | load the usbmon module (if built as module). The second step is skipped | |
28 | if usbmon is built into the kernel. | |
29 | ||
30 | # mount -t debugfs none_debugs /sys/kernel/debug | |
31 | # modprobe usbmon | |
d9ac2cfc | 32 | # |
1da177e4 LT |
33 | |
34 | Verify that bus sockets are present. | |
35 | ||
d9ac2cfc | 36 | # ls /sys/kernel/debug/usbmon |
1da177e4 | 37 | 1s 1t 2s 2t 3s 3t 4s 4t |
d9ac2cfc | 38 | # |
1da177e4 LT |
39 | |
40 | 2. Find which bus connects to the desired device | |
41 | ||
42 | Run "cat /proc/bus/usb/devices", and find the T-line which corresponds to | |
43 | the device. Usually you do it by looking for the vendor string. If you have | |
44 | many similar devices, unplug one and compare two /proc/bus/usb/devices outputs. | |
45 | The T-line will have a bus number. Example: | |
46 | ||
47 | T: Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 0 | |
48 | D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1 | |
49 | P: Vendor=0557 ProdID=2004 Rev= 1.00 | |
50 | S: Manufacturer=ATEN | |
51 | S: Product=UC100KM V2.00 | |
52 | ||
53 | Bus=03 means it's bus 3. | |
54 | ||
55 | 3. Start 'cat' | |
56 | ||
57 | # cat /sys/kernel/debug/usbmon/3t > /tmp/1.mon.out | |
58 | ||
59 | This process will be reading until killed. Naturally, the output can be | |
60 | redirected to a desirable location. This is preferred, because it is going | |
61 | to be quite long. | |
62 | ||
63 | 4. Perform the desired operation on the USB bus | |
64 | ||
65 | This is where you do something that creates the traffic: plug in a flash key, | |
66 | copy files, control a webcam, etc. | |
67 | ||
68 | 5. Kill cat | |
69 | ||
70 | Usually it's done with a keyboard interrupt (Control-C). | |
71 | ||
72 | At this point the output file (/tmp/1.mon.out in this example) can be saved, | |
73 | sent by e-mail, or inspected with a text editor. In the last case make sure | |
74 | that the file size is not excessive for your favourite editor. | |
75 | ||
76 | * Raw text data format | |
77 | ||
d9ac2cfc | 78 | The '1t' type data consists of a stream of events, such as URB submission, |
1da177e4 LT |
79 | URB callback, submission error. Every event is a text line, which consists |
80 | of whitespace separated words. The number of position of words may depend | |
81 | on the event type, but there is a set of words, common for all types. | |
82 | ||
83 | Here 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 | |
d9ac2cfc PZ |
99 | 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. | |
ae0d6cce PZ |
110 | - 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. | |
d9ac2cfc PZ |
114 | - Data Length. For submissions, this is the requested length. For callbacks, |
115 | this is the actual length. | |
1da177e4 | 116 | - Data tag. The usbmon may not always capture data, even if length is nonzero. |
d9ac2cfc | 117 | The data words are present only if this tag is '='. |
1da177e4 LT |
118 | - 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 | ||
124 | Here is an example of code to read the data stream in a well known programming | |
125 | language: | |
126 | ||
127 | class 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; | |
ae0d6cce | 139 | int b; // byte is signed, apparently?! XXX |
1da177e4 | 140 | for (i = 0; i < len; i++) { |
ae0d6cce PZ |
141 | // 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; | |
1da177e4 LT |
150 | data_len++; |
151 | } | |
152 | } | |
153 | } | |
154 | } | |
155 | ||
ae0d6cce | 156 | This format may be changed in the future. |
1da177e4 LT |
157 | |
158 | Examples: | |
159 | ||
ae0d6cce | 160 | An input control transfer to get a port status. |
1da177e4 | 161 | |
ae0d6cce PZ |
162 | d5ea89a0 3575914555 S Ci:001:00 s a3 00 0000 0003 0004 4 < |
163 | d5ea89a0 3575914560 C Ci:001:00 0 4 = 01050000 | |
1da177e4 LT |
164 | |
165 | An output bulk transfer to send a SCSI command 0x5E in a 31-byte Bulk wrapper | |
166 | to a storage device at address 5: | |
167 | ||
168 | dd65f0e8 4128379752 S Bo:005:02 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000 | |
169 | dd65f0e8 4128379808 C Bo:005:02 0 31 > | |
170 | ||
171 | * Raw binary format and API | |
172 | ||
173 | TBD |