174 строки
6.7 KiB
Plaintext
174 строки
6.7 KiB
Plaintext
* 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.
|
|
|
|
# ls /sys/kernel/debug/usbmon
|
|
1s 1t 2s 2t 3s 3t 4s 4t
|
|
#
|
|
|
|
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 '1t' 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 3-digit and 2-digit (respectively)
|
|
decimal numbers, with leading zeroes.
|
|
- URB Status. In most cases, this field contains a number, sometimes negative,
|
|
which represents a "status" field of the URB. This field makes no sense for
|
|
submissions, but is present anyway to help scripts with parsing. When an
|
|
error occurs, the field contains the error code. In case of a submission of
|
|
a Control packet, this field contains a Setup Tag instead of an error code.
|
|
It is easy to tell whether the Setup Tag is present because it is never a
|
|
number. Thus if scripts find a number in this field, they proceed to read
|
|
Data Length. If they find something else, like a letter, 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. For submissions, this is the requested length. For callbacks,
|
|
this is the actual length.
|
|
- Data tag. The usbmon may not always capture data, even if length is nonzero.
|
|
The data words are present only if this tag is '='.
|
|
- 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
|