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Linus Torvalds1da177e2005-04-16 15:20:36 -07001* 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
Pete Zaitcevf1c9e302007-02-24 19:27:33 -080019common trace exchange format for tools while more sophisticated formats
Linus Torvalds1da177e2005-04-16 15:20:36 -070020are 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
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -070032#
Linus Torvalds1da177e2005-04-16 15:20:36 -070033
34Verify that bus sockets are present.
35
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -070036# ls /sys/kernel/debug/usbmon
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800371s 1t 1u 2s 2t 2u 3s 3t 3u 4s 4t 4u
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -070038#
Linus Torvalds1da177e2005-04-16 15:20:36 -070039
402. Find which bus connects to the desired device
41
42Run "cat /proc/bus/usb/devices", and find the T-line which corresponds to
43the device. Usually you do it by looking for the vendor string. If you have
44many similar devices, unplug one and compare two /proc/bus/usb/devices outputs.
45The T-line will have a bus number. Example:
46
47T: Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 0
48D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
49P: Vendor=0557 ProdID=2004 Rev= 1.00
50S: Manufacturer=ATEN
51S: Product=UC100KM V2.00
52
53Bus=03 means it's bus 3.
54
553. Start 'cat'
56
Pete Zaitcevf1c9e302007-02-24 19:27:33 -080057# cat /sys/kernel/debug/usbmon/3u > /tmp/1.mon.out
Linus Torvalds1da177e2005-04-16 15:20:36 -070058
59This process will be reading until killed. Naturally, the output can be
60redirected to a desirable location. This is preferred, because it is going
61to be quite long.
62
634. Perform the desired operation on the USB bus
64
65This is where you do something that creates the traffic: plug in a flash key,
66copy files, control a webcam, etc.
67
685. Kill cat
69
70Usually it's done with a keyboard interrupt (Control-C).
71
72At this point the output file (/tmp/1.mon.out in this example) can be saved,
73sent by e-mail, or inspected with a text editor. In the last case make sure
74that the file size is not excessive for your favourite editor.
75
76* Raw text data format
77
Pete Zaitcevf1c9e302007-02-24 19:27:33 -080078Two formats are supported currently: the original, or '1t' format, and
79the '1u' format. The '1t' format is deprecated in kernel 2.6.21. The '1u'
80format adds a few fields, such as ISO frame descriptors, interval, etc.
81It produces slightly longer lines, but otherwise is a perfect superset
82of '1t' format.
83
84If it is desired to recognize one from the other in a program, look at the
85"address" word (see below), where '1u' format adds a bus number. If 2 colons
86are present, it's the '1t' format, otherwise '1u'.
87
88Any text format data consists of a stream of events, such as URB submission,
Linus Torvalds1da177e2005-04-16 15:20:36 -070089URB callback, submission error. Every event is a text line, which consists
Pete Zaitcev6f23ee12006-12-30 22:43:10 -080090of whitespace separated words. The number or position of words may depend
Linus Torvalds1da177e2005-04-16 15:20:36 -070091on the event type, but there is a set of words, common for all types.
92
93Here is the list of words, from left to right:
Pete Zaitcevf1c9e302007-02-24 19:27:33 -080094
Linus Torvalds1da177e2005-04-16 15:20:36 -070095- URB Tag. This is used to identify URBs is normally a kernel mode address
96 of the URB structure in hexadecimal.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -080097
Linus Torvalds1da177e2005-04-16 15:20:36 -070098- Timestamp in microseconds, a decimal number. The timestamp's resolution
99 depends on available clock, and so it can be much worse than a microsecond
100 (if the implementation uses jiffies, for example).
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800101
Linus Torvalds1da177e2005-04-16 15:20:36 -0700102- Event Type. This type refers to the format of the event, not URB type.
103 Available types are: S - submission, C - callback, E - submission error.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800104
105- "Address" word (formerly a "pipe"). It consists of four fields, separated by
106 colons: URB type and direction, Bus number, Device address, Endpoint number.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700107 Type and direction are encoded with two bytes in the following manner:
108 Ci Co Control input and output
109 Zi Zo Isochronous input and output
110 Ii Io Interrupt input and output
111 Bi Bo Bulk input and output
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800112 Bus number, Device address, and Endpoint are decimal numbers, but they may
113 have leading zeros, for the sake of human readers.
114
115- URB Status word. This is either a letter, or several numbers separated
116 by colons: URB status, interval, start frame, and error count. Unlike the
117 "address" word, all fields save the status are optional. Interval is printed
118 only for interrupt and isochronous URBs. Start frame is printed only for
119 isochronous URBs. Error count is printed only for isochronous callback
120 events.
121
122 The status field is a decimal number, sometimes negative, which represents
123 a "status" field of the URB. This field makes no sense for submissions, but
124 is present anyway to help scripts with parsing. When an error occurs, the
125 field contains the error code.
126
127 In case of a submission of a Control packet, this field contains a Setup Tag
128 instead of an group of numbers. It is easy to tell whether the Setup Tag is
129 present because it is never a number. Thus if scripts find a set of numbers
130 in this word, they proceed to read Data Length (except for isochronous URBs).
131 If they find something else, like a letter, they read the setup packet before
132 reading the Data Length or isochronous descriptors.
133
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700134- Setup packet, if present, consists of 5 words: one of each for bmRequestType,
135 bRequest, wValue, wIndex, wLength, as specified by the USB Specification 2.0.
136 These words are safe to decode if Setup Tag was 's'. Otherwise, the setup
137 packet was present, but not captured, and the fields contain filler.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800138
139- Number of isochronous frame descriptors and descriptors themselves.
140 If an Isochronous transfer event has a set of descriptors, a total number
141 of them in an URB is printed first, then a word per descriptor, up to a
142 total of 5. The word consists of 3 colon-separated decimal numbers for
143 status, offset, and length respectively. For submissions, initial length
144 is reported. For callbacks, actual length is reported.
145
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -0700146- Data Length. For submissions, this is the requested length. For callbacks,
147 this is the actual length.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800148
Linus Torvalds1da177e2005-04-16 15:20:36 -0700149- Data tag. The usbmon may not always capture data, even if length is nonzero.
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -0700150 The data words are present only if this tag is '='.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800151
Linus Torvalds1da177e2005-04-16 15:20:36 -0700152- Data words follow, in big endian hexadecimal format. Notice that they are
153 not machine words, but really just a byte stream split into words to make
154 it easier to read. Thus, the last word may contain from one to four bytes.
155 The length of collected data is limited and can be less than the data length
156 report in Data Length word.
157
158Here is an example of code to read the data stream in a well known programming
159language:
160
161class ParsedLine {
162 int data_len; /* Available length of data */
163 byte data[];
164
165 void parseData(StringTokenizer st) {
166 int availwords = st.countTokens();
167 data = new byte[availwords * 4];
168 data_len = 0;
169 while (st.hasMoreTokens()) {
170 String data_str = st.nextToken();
171 int len = data_str.length() / 2;
172 int i;
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700173 int b; // byte is signed, apparently?! XXX
Linus Torvalds1da177e2005-04-16 15:20:36 -0700174 for (i = 0; i < len; i++) {
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700175 // data[data_len] = Byte.parseByte(
176 // data_str.substring(i*2, i*2 + 2),
177 // 16);
178 b = Integer.parseInt(
179 data_str.substring(i*2, i*2 + 2),
180 16);
181 if (b >= 128)
182 b *= -1;
183 data[data_len] = (byte) b;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700184 data_len++;
185 }
186 }
187 }
188}
189
Linus Torvalds1da177e2005-04-16 15:20:36 -0700190Examples:
191
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700192An input control transfer to get a port status.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700193
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800194d5ea89a0 3575914555 S Ci:1:001:0 s a3 00 0000 0003 0004 4 <
195d5ea89a0 3575914560 C Ci:1:001:0 0 4 = 01050000
Linus Torvalds1da177e2005-04-16 15:20:36 -0700196
197An output bulk transfer to send a SCSI command 0x5E in a 31-byte Bulk wrapper
198to a storage device at address 5:
199
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800200dd65f0e8 4128379752 S Bo:1:005:2 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000
201dd65f0e8 4128379808 C Bo:1:005:2 0 31 >
Linus Torvalds1da177e2005-04-16 15:20:36 -0700202
203* Raw binary format and API
204
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800205The overall architecture of the API is about the same as the one above,
206only the events are delivered in binary format. Each event is sent in
207the following structure (its name is made up, so that we can refer to it):
208
209struct usbmon_packet {
210 u64 id; /* 0: URB ID - from submission to callback */
211 unsigned char type; /* 8: Same as text; extensible. */
212 unsigned char xfer_type; /* ISO (0), Intr, Control, Bulk (3) */
213 unsigned char epnum; /* Endpoint number and transfer direction */
214 unsigned char devnum; /* Device address */
215 u16 busnum; /* 12: Bus number */
216 char flag_setup; /* 14: Same as text */
217 char flag_data; /* 15: Same as text; Binary zero is OK. */
218 s64 ts_sec; /* 16: gettimeofday */
219 s32 ts_usec; /* 24: gettimeofday */
220 int status; /* 28: */
221 unsigned int length; /* 32: Length of data (submitted or actual) */
222 unsigned int len_cap; /* 36: Delivered length */
223 unsigned char setup[8]; /* 40: Only for Control 'S' */
224}; /* 48 bytes total */
225
226These events can be received from a character device by reading with read(2),
227with an ioctl(2), or by accessing the buffer with mmap.
228
229The character device is usually called /dev/usbmonN, where N is the USB bus
230number. Number zero (/dev/usbmon0) is special and means "all buses".
231However, this feature is not implemented yet. Note that specific naming
232policy is set by your Linux distribution.
233
234If you create /dev/usbmon0 by hand, make sure that it is owned by root
235and has mode 0600. Otherwise, unpriviledged users will be able to snoop
236keyboard traffic.
237
238The following ioctl calls are available, with MON_IOC_MAGIC 0x92:
239
240 MON_IOCQ_URB_LEN, defined as _IO(MON_IOC_MAGIC, 1)
241
242This call returns the length of data in the next event. Note that majority of
243events contain no data, so if this call returns zero, it does not mean that
244no events are available.
245
246 MON_IOCG_STATS, defined as _IOR(MON_IOC_MAGIC, 3, struct mon_bin_stats)
247
248The argument is a pointer to the following structure:
249
250struct mon_bin_stats {
251 u32 queued;
252 u32 dropped;
253};
254
255The member "queued" refers to the number of events currently queued in the
256buffer (and not to the number of events processed since the last reset).
257
258The member "dropped" is the number of events lost since the last call
259to MON_IOCG_STATS.
260
261 MON_IOCT_RING_SIZE, defined as _IO(MON_IOC_MAGIC, 4)
262
263This call sets the buffer size. The argument is the size in bytes.
264The size may be rounded down to the next chunk (or page). If the requested
265size is out of [unspecified] bounds for this kernel, the call fails with
266-EINVAL.
267
268 MON_IOCQ_RING_SIZE, defined as _IO(MON_IOC_MAGIC, 5)
269
270This call returns the current size of the buffer in bytes.
271
272 MON_IOCX_GET, defined as _IOW(MON_IOC_MAGIC, 6, struct mon_get_arg)
273
274This call waits for events to arrive if none were in the kernel buffer,
275then returns the first event. Its argument is a pointer to the following
276structure:
277
278struct mon_get_arg {
279 struct usbmon_packet *hdr;
280 void *data;
281 size_t alloc; /* Length of data (can be zero) */
282};
283
284Before the call, hdr, data, and alloc should be filled. Upon return, the area
285pointed by hdr contains the next event structure, and the data buffer contains
286the data, if any. The event is removed from the kernel buffer.
287
288 MON_IOCX_MFETCH, defined as _IOWR(MON_IOC_MAGIC, 7, struct mon_mfetch_arg)
289
290This ioctl is primarily used when the application accesses the buffer
291with mmap(2). Its argument is a pointer to the following structure:
292
293struct mon_mfetch_arg {
294 uint32_t *offvec; /* Vector of events fetched */
295 uint32_t nfetch; /* Number of events to fetch (out: fetched) */
296 uint32_t nflush; /* Number of events to flush */
297};
298
299The ioctl operates in 3 stages.
300
301First, it removes and discards up to nflush events from the kernel buffer.
302The actual number of events discarded is returned in nflush.
303
304Second, it waits for an event to be present in the buffer, unless the pseudo-
305device is open with O_NONBLOCK.
306
307Third, it extracts up to nfetch offsets into the mmap buffer, and stores
308them into the offvec. The actual number of event offsets is stored into
309the nfetch.
310
311 MON_IOCH_MFLUSH, defined as _IO(MON_IOC_MAGIC, 8)
312
313This call removes a number of events from the kernel buffer. Its argument
314is the number of events to remove. If the buffer contains fewer events
315than requested, all events present are removed, and no error is reported.
316This works when no events are available too.
317
318 FIONBIO
319
320The ioctl FIONBIO may be implemented in the future, if there's a need.
321
322In addition to ioctl(2) and read(2), the special file of binary API can
323be polled with select(2) and poll(2). But lseek(2) does not work.
324
325* Memory-mapped access of the kernel buffer for the binary API
326
327The basic idea is simple:
328
329To prepare, map the buffer by getting the current size, then using mmap(2).
330Then, execute a loop similar to the one written in pseudo-code below:
331
332 struct mon_mfetch_arg fetch;
333 struct usbmon_packet *hdr;
334 int nflush = 0;
335 for (;;) {
336 fetch.offvec = vec; // Has N 32-bit words
337 fetch.nfetch = N; // Or less than N
338 fetch.nflush = nflush;
339 ioctl(fd, MON_IOCX_MFETCH, &fetch); // Process errors, too
340 nflush = fetch.nfetch; // This many packets to flush when done
341 for (i = 0; i < nflush; i++) {
342 hdr = (struct ubsmon_packet *) &mmap_area[vec[i]];
343 if (hdr->type == '@') // Filler packet
344 continue;
345 caddr_t data = &mmap_area[vec[i]] + 64;
346 process_packet(hdr, data);
347 }
348 }
349
350Thus, the main idea is to execute only one ioctl per N events.
351
352Although the buffer is circular, the returned headers and data do not cross
353the end of the buffer, so the above pseudo-code does not need any gathering.