aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation/usb/usbmon.txt
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/usb/usbmon.txt
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'Documentation/usb/usbmon.txt')
-rw-r--r--Documentation/usb/usbmon.txt156
1 files changed, 156 insertions, 0 deletions
diff --git a/Documentation/usb/usbmon.txt b/Documentation/usb/usbmon.txt
new file mode 100644
index 000000000000..2f8431f92b77
--- /dev/null
+++ b/Documentation/usb/usbmon.txt
@@ -0,0 +1,156 @@
1* Introduction
2
3The name "usbmon" in lowercase refers to a facility in kernel which is
4used to collect traces of I/O on the USB bus. This function is analogous
5to a packet socket used by network monitoring tools such as tcpdump(1)
6or Ethereal. Similarly, it is expected that a tool such as usbdump or
7USBMon (with uppercase letters) is used to examine raw traces produced
8by usbmon.
9
10The usbmon reports requests made by peripheral-specific drivers to Host
11Controller Drivers (HCD). So, if HCD is buggy, the traces reported by
12usbmon may not correspond to bus transactions precisely. This is the same
13situation as with tcpdump.
14
15* How to use usbmon to collect raw text traces
16
17Unlike the packet socket, usbmon has an interface which provides traces
18in a text format. This is used for two purposes. First, it serves as a
19common trace exchange format for tools while most sophisticated formats
20are finalized. Second, humans can read it in case tools are not available.
21
22To collect a raw text trace, execute following steps.
23
241. Prepare
25
26Mount debugfs (it has to be enabled in your kernel configuration), and
27load the usbmon module (if built as module). The second step is skipped
28if usbmon is built into the kernel.
29
30# mount -t debugfs none_debugs /sys/kernel/debug
31# modprobe usbmon
32
33Verify that bus sockets are present.
34
35[root@lembas zaitcev]# ls /sys/kernel/debug/usbmon
361s 1t 2s 2t 3s 3t 4s 4t
37[root@lembas zaitcev]#
38
39# ls /sys/kernel
40
412. Find which bus connects to the desired device
42
43Run "cat /proc/bus/usb/devices", and find the T-line which corresponds to
44the device. Usually you do it by looking for the vendor string. If you have
45many similar devices, unplug one and compare two /proc/bus/usb/devices outputs.
46The T-line will have a bus number. Example:
47
48T: Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 0
49D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
50P: Vendor=0557 ProdID=2004 Rev= 1.00
51S: Manufacturer=ATEN
52S: Product=UC100KM V2.00
53
54Bus=03 means it's bus 3.
55
563. Start 'cat'
57
58# cat /sys/kernel/debug/usbmon/3t > /tmp/1.mon.out
59
60This process will be reading until killed. Naturally, the output can be
61redirected to a desirable location. This is preferred, because it is going
62to be quite long.
63
644. Perform the desired operation on the USB bus
65
66This is where you do something that creates the traffic: plug in a flash key,
67copy files, control a webcam, etc.
68
695. Kill cat
70
71Usually it's done with a keyboard interrupt (Control-C).
72
73At this point the output file (/tmp/1.mon.out in this example) can be saved,
74sent by e-mail, or inspected with a text editor. In the last case make sure
75that the file size is not excessive for your favourite editor.
76
77* Raw text data format
78
79The '0t' type data consists of a stream of events, such as URB submission,
80URB callback, submission error. Every event is a text line, which consists
81of whitespace separated words. The number of position of words may depend
82on the event type, but there is a set of words, common for all types.
83
84Here 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- Data Length. This is the actual length in the URB.
105- Data tag. The usbmon may not always capture data, even if length is nonzero.
106 Only if tag is '=', the data words are present.
107- Data words follow, in big endian hexadecimal format. Notice that they are
108 not machine words, but really just a byte stream split into words to make
109 it easier to read. Thus, the last word may contain from one to four bytes.
110 The length of collected data is limited and can be less than the data length
111 report in Data Length word.
112
113Here is an example of code to read the data stream in a well known programming
114language:
115
116class ParsedLine {
117 int data_len; /* Available length of data */
118 byte data[];
119
120 void parseData(StringTokenizer st) {
121 int availwords = st.countTokens();
122 data = new byte[availwords * 4];
123 data_len = 0;
124 while (st.hasMoreTokens()) {
125 String data_str = st.nextToken();
126 int len = data_str.length() / 2;
127 int i;
128 for (i = 0; i < len; i++) {
129 data[data_len] = Byte.parseByte(
130 data_str.substring(i*2, i*2 + 2),
131 16);
132 data_len++;
133 }
134 }
135 }
136}
137
138This format is obviously deficient. For example, the setup packet for control
139transfers is not delivered. This will change in the future.
140
141Examples:
142
143An input control transfer to get a port status:
144
145d74ff9a0 2640288196 S Ci:001:00 -115 4 <
146d74ff9a0 2640288202 C Ci:001:00 0 4 = 01010100
147
148An output bulk transfer to send a SCSI command 0x5E in a 31-byte Bulk wrapper
149to a storage device at address 5:
150
151dd65f0e8 4128379752 S Bo:005:02 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000
152dd65f0e8 4128379808 C Bo:005:02 0 31 >
153
154* Raw binary format and API
155
156TBD