Documentation/usb/usbmon.txt - linux - Git at Google

 * 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.
   In case of a setup packet, it contains a Setup Tag. If scripts read a number
   in this field, they proceed to read Data Length. Otherwise, they read
   the setup packet before reading the Data Length.
 - 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.
 - 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
 language:

 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;
 			int b;	// byte is signed, apparently?! XXX
 			for (i = 0; i < len; i++) {
 				// data[data_len] = Byte.parseByte(
 				//     data_str.substring(i*2, i*2 + 2),
 				//     16);
 				b = Integer.parseInt(
 				     data_str.substring(i*2, i*2 + 2),
 				     16);
 				if (b >= 128)
 					b *= -1;
 				data[data_len] = (byte) b;
 				data_len++;
 			}
 		}
 	}
 }

 This format may be changed in the future.

 Examples:

 An input control transfer to get a port status.

 d5ea89a0 3575914555 S Ci:001:00 s a3 00 0000 0003 0004 4 <
 d5ea89a0 3575914560 C Ci:001:00 0 4 = 01050000

 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

 TBD
	* 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.
	In case of a setup packet, it contains a Setup Tag. If scripts read a number
	in this field, they proceed to read Data Length. Otherwise, they read
	the setup packet before reading the Data Length.
	- 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.
	- 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
	language:

	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;
	int b; // byte is signed, apparently?! XXX
	for (i = 0; i < len; i++) {
	// data[data_len] = Byte.parseByte(
	// data_str.substring(i2, i2 + 2),
	// 16);
	b = Integer.parseInt(
	data_str.substring(i2, i2 + 2),
	16);
	if (b >= 128)
	b *= -1;
	data[data_len] = (byte) b;
	data_len++;
	}
	}
	}
	}

	This format may be changed in the future.

	Examples:

	An input control transfer to get a port status.

	d5ea89a0 3575914555 S Ci:001:00 s a3 00 0000 0003 0004 4 <
	d5ea89a0 3575914560 C Ci:001:00 0 4 = 01050000

	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

	TBD