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+* Introduction
+The name "usbmon" in lowercase refers to a facility in kernel which is
+used to collect traces of I/O on the USB bus. This function is analogous
+to a packet socket used by network monitoring tools such as tcpdump(1)
+or Ethereal. Similarly, it is expected that a tool such as usbdump or
+USBMon (with uppercase letters) is used to examine raw traces produced
+by usbmon.
+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.
+* How to use usbmon to collect raw text traces
+Unlike the packet socket, usbmon has an interface which provides traces
+in a text format. This is used for two purposes. First, it serves as a
+common trace exchange format for tools while most sophisticated formats
+are finalized. Second, humans can read it in case tools are not available.
+To collect a raw text trace, execute following steps.
+1. Prepare
+Mount debugfs (it has to be enabled in your kernel configuration), and
+load the usbmon module (if built as module). The second step is skipped
+if usbmon is built into the kernel.
+# mount -t debugfs none_debugs /sys/kernel/debug
+# modprobe usbmon
+Verify that bus sockets are present.
+[root@lembas zaitcev]# ls /sys/kernel/debug/usbmon
+1s 1t 2s 2t 3s 3t 4s 4t
+[root@lembas zaitcev]#
+# ls /sys/kernel
+2. Find which bus connects to the desired device
+Run "cat /proc/bus/usb/devices", and find the T-line which corresponds to
+the device. Usually you do it by looking for the vendor string. If you have
+many similar devices, unplug one and compare two /proc/bus/usb/devices outputs.
+The T-line will have a bus number. Example:
+T: Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 0
+D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
+P: Vendor=0557 ProdID=2004 Rev= 1.00
+S: Manufacturer=ATEN
+S: Product=UC100KM V2.00
+Bus=03 means it's bus 3.
+3. Start 'cat'
+# cat /sys/kernel/debug/usbmon/3t > /tmp/1.mon.out
+This process will be reading until killed. Naturally, the output can be
+redirected to a desirable location. This is preferred, because it is going
+to be quite long.
+4. Perform the desired operation on the USB bus
+This is where you do something that creates the traffic: plug in a flash key,
+copy files, control a webcam, etc.
+5. Kill cat
+Usually it's done with a keyboard interrupt (Control-C).
+At this point the output file (/tmp/1.mon.out in this example) can be saved,
+sent by e-mail, or inspected with a text editor. In the last case make sure
+that the file size is not excessive for your favourite editor.
+* Raw text data format
+The '0t' type data consists of a stream of events, such as URB submission,
+URB callback, submission error. Every event is a text line, which consists
+of whitespace separated words. The number of position of words may depend
+on the event type, but there is a set of words, common for all types.
+Here is the list of words, from left to right:
+- URB Tag. This is used to identify URBs is normally a kernel mode address
+ of the URB structure in hexadecimal.
+- Timestamp in 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).
+- Event Type. This type refers to the format of the event, not URB type.
+ Available types are: S - submission, C - callback, E - submission error.
+- "Pipe". The pipe concept is deprecated. This is a composite word, used to
+ be derived from information in pipes. It consists of three fields, separated
+ by colons: URB type and direction, 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
+ Device address and Endpoint number are decimal numbers with leading zeroes
+ or 3 and 2 positions, correspondingly.
+- URB Status. This field makes no sense for submissions, but is present
+ to help scripts with parsing. In error case, it contains the error code.
+- Data Length. This is the actual length in the URB.
+- Data tag. The usbmon may not always capture data, even if length is nonzero.
+ Only if tag is '=', the data words are present.
+- 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
+ report in Data Length word.
+Here is an example of code to read the data stream in a well known programming
+class ParsedLine {
+ int data_len; /* Available length of data */
+ byte data[];
+ void parseData(StringTokenizer st) {
+ int availwords = st.countTokens();
+ data = new byte[availwords * 4];
+ data_len = 0;
+ while (st.hasMoreTokens()) {
+ String data_str = st.nextToken();
+ int len = data_str.length() / 2;
+ int i;
+ for (i = 0; i < len; i++) {
+ data[data_len] = Byte.parseByte(
+ data_str.substring(i*2, i*2 + 2),
+ 16);
+ data_len++;
+ }
+ }
+ }
+This format is obviously deficient. For example, the setup packet for control
+transfers is not delivered. This will change in the future.
+An input control transfer to get a port status:
+d74ff9a0 2640288196 S Ci:001:00 -115 4 <
+d74ff9a0 2640288202 C Ci:001:00 0 4 = 01010100
+An output bulk transfer to send a SCSI command 0x5E in a 31-byte Bulk wrapper
+to a storage device at address 5:
+dd65f0e8 4128379752 S Bo:005:02 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000
+dd65f0e8 4128379808 C Bo:005:02 0 31 >
+* Raw binary format and API