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diff --git a/Documentation/usb/usbmon.txt b/Documentation/usb/usbmon.txt new file mode 100644 index 00000000000..2f8431f92b7 --- /dev/null +++ b/Documentation/usb/usbmon.txt @@ -0,0 +1,156 @@ +* 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 +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; + 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. + +Examples: + +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 + +TBD |