Documentation/usb/usbmon.txt

   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
  32
  33 Verify that bus sockets are present.
  34
  35 [root@lembas zaitcev]# ls /sys/kernel/debug/usbmon
  36 1s  1t  2s  2t  3s  3t  4s  4t
  37 [root@lembas zaitcev]#
  38
  39 # ls /sys/kernel
  40
  41 2. Find which bus connects to the desired device
  42
  43 Run "cat /proc/bus/usb/devices", and find the T-line which corresponds to
  44 the device. Usually you do it by looking for the vendor string. If you have
  45 many similar devices, unplug one and compare two /proc/bus/usb/devices outputs.
  46 The T-line will have a bus number. Example:
  47
  48 T:  Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=12  MxCh= 0
  49 D:  Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
  50 P:  Vendor=0557 ProdID=2004 Rev= 1.00
  51 S:  Manufacturer=ATEN
  52 S:  Product=UC100KM V2.00
  53
  54 Bus=03 means it's bus 3.
  55
  56 3. Start 'cat'
  57
  58 # cat /sys/kernel/debug/usbmon/3t > /tmp/1.mon.out
  59
  60 This process will be reading until killed. Naturally, the output can be
  61 redirected to a desirable location. This is preferred, because it is going
  62 to be quite long.
  63
  64 4. Perform the desired operation on the USB bus
  65
  66 This is where you do something that creates the traffic: plug in a flash key,
  67 copy files, control a webcam, etc.
  68
  69 5. Kill cat
  70
  71 Usually it's done with a keyboard interrupt (Control-C).
  72
  73 At this point the output file (/tmp/1.mon.out in this example) can be saved,
  74 sent by e-mail, or inspected with a text editor. In the last case make sure
  75 that the file size is not excessive for your favourite editor.
  76
  77 * Raw text data format
  78
  79 The '0t' type data consists of a stream of events, such as URB submission,
  80 URB callback, submission error. Every event is a text line, which consists
  81 of whitespace separated words. The number of position of words may depend
  82 on the event type, but there is a set of words, common for all types.
  83
  84 Here is the list of words, from left to right:
  85 - URB Tag. This is used to identify URBs is normally a kernel mode address
  86  of the URB structure in hexadecimal.
  87 - Timestamp in microseconds, a decimal number. The timestamp's resolution
  88   depends on available clock, and so it can be much worse than a microsecond
  89   (if the implementation uses jiffies, for example).
  90 - Event Type. This type refers to the format of the event, not URB type.
  91   Available types are: S - submission, C - callback, E - submission error.
  92 - "Pipe". The pipe concept is deprecated. This is a composite word, used to
  93   be derived from information in pipes. It consists of three fields, separated
  94   by colons: URB type and direction, Device address, Endpoint number.
  95   Type and direction are encoded with two bytes in the following manner:
  96     Ci Co   Control input and output
  97     Zi Zo   Isochronous input and output
  98     Ii Io   Interrupt input and output
  99     Bi Bo   Bulk input and output
 100   Device address and Endpoint number are decimal numbers with leading zeroes
 101   or 3 and 2 positions, correspondingly.
 102 - URB Status. This field makes no sense for submissions, but is present
 103   to help scripts with parsing. In error case, it contains the error code.
 104   In case of a setup packet, it contains a Setup Tag. If scripts read a number
 105   in this field, they proceed to read Data Length. Otherwise, they read
 106   the setup packet before reading the Data Length.
 107 - Setup packet, if present, consists of 5 words: one of each for bmRequestType,
 108   bRequest, wValue, wIndex, wLength, as specified by the USB Specification 2.0.
 109   These words are safe to decode if Setup Tag was 's'. Otherwise, the setup
 110   packet was present, but not captured, and the fields contain filler.
 111 - Data Length. This is the actual length in the URB.
 112 - Data tag. The usbmon may not always capture data, even if length is nonzero.
 113   Only if tag is '=', the data words are present.
 114 - Data words follow, in big endian hexadecimal format. Notice that they are
 115   not machine words, but really just a byte stream split into words to make
 116   it easier to read. Thus, the last word may contain from one to four bytes.
 117   The length of collected data is limited and can be less than the data length
 118   report in Data Length word.
 119
 120 Here is an example of code to read the data stream in a well known programming
 121 language:
 122
 123 class ParsedLine {
 124         int data_len;           /* Available length of data */
 125         byte data[];
 126
 127         void parseData(StringTokenizer st) {
 128                 int availwords = st.countTokens();
 129                 data = new byte[availwords * 4];
 130                 data_len = 0;
 131                 while (st.hasMoreTokens()) {
 132                         String data_str = st.nextToken();
 133                         int len = data_str.length() / 2;
 134                         int i;
 135                         int b;  // byte is signed, apparently?! XXX
 136                         for (i = 0; i < len; i++) {
 137                                 // data[data_len] = Byte.parseByte(
 138                                 //     data_str.substring(i*2, i*2 + 2),
 139                                 //     16);
 140                                 b = Integer.parseInt(
 141                                      data_str.substring(i*2, i*2 + 2),
 142                                      16);
 143                                 if (b >= 128)
 144                                         b *= -1;
 145                                 data[data_len] = (byte) b;
 146                                 data_len++;
 147                         }
 148                 }
 149         }
 150 }
 151
 152 This format may be changed in the future.
 153
 154 Examples:
 155
 156 An input control transfer to get a port status.
 157
 158 d5ea89a0 3575914555 S Ci:001:00 s a3 00 0000 0003 0004 4 <
 159 d5ea89a0 3575914560 C Ci:001:00 0 4 = 01050000
 160
 161 An output bulk transfer to send a SCSI command 0x5E in a 31-byte Bulk wrapper
 162 to a storage device at address 5:
 163
 164 dd65f0e8 4128379752 S Bo:005:02 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000
 165 dd65f0e8 4128379808 C Bo:005:02 0 31 >
 166
 167 * Raw binary format and API
 168
 169 TBD