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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 Zaitcevaacf4a02008-12-04 16:17:00 -0700370s 0u 1s 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
Pete Zaitcevaacf4a02008-12-04 16:17:00 -070040Now you can choose to either use the socket '0u' (to capture packets on all
41buses), and skip to step #3, or find the bus used by your device with step #2.
42This allows to filter away annoying devices that talk continuously.
Paolo 'Blaisorblade' Giarrusso092a2122007-08-24 12:19:22 +020043
Linus Torvalds1da177e2005-04-16 15:20:36 -0700442. Find which bus connects to the desired device
45
46Run "cat /proc/bus/usb/devices", and find the T-line which corresponds to
47the device. Usually you do it by looking for the vendor string. If you have
48many similar devices, unplug one and compare two /proc/bus/usb/devices outputs.
49The T-line will have a bus number. Example:
50
51T: Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 0
52D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
53P: Vendor=0557 ProdID=2004 Rev= 1.00
54S: Manufacturer=ATEN
55S: Product=UC100KM V2.00
56
57Bus=03 means it's bus 3.
58
593. Start 'cat'
60
Pete Zaitcevf1c9e302007-02-24 19:27:33 -080061# cat /sys/kernel/debug/usbmon/3u > /tmp/1.mon.out
Linus Torvalds1da177e2005-04-16 15:20:36 -070062
Paolo 'Blaisorblade' Giarrusso092a2122007-08-24 12:19:22 +020063to listen on a single bus, otherwise, to listen on all buses, type:
64
65# cat /sys/kernel/debug/usbmon/0u > /tmp/1.mon.out
66
Linus Torvalds1da177e2005-04-16 15:20:36 -070067This process will be reading until killed. Naturally, the output can be
68redirected to a desirable location. This is preferred, because it is going
69to be quite long.
70
714. Perform the desired operation on the USB bus
72
73This is where you do something that creates the traffic: plug in a flash key,
74copy files, control a webcam, etc.
75
765. Kill cat
77
78Usually it's done with a keyboard interrupt (Control-C).
79
80At this point the output file (/tmp/1.mon.out in this example) can be saved,
81sent by e-mail, or inspected with a text editor. In the last case make sure
82that the file size is not excessive for your favourite editor.
83
84* Raw text data format
85
Pete Zaitcevf1c9e302007-02-24 19:27:33 -080086Two formats are supported currently: the original, or '1t' format, and
87the '1u' format. The '1t' format is deprecated in kernel 2.6.21. The '1u'
88format adds a few fields, such as ISO frame descriptors, interval, etc.
89It produces slightly longer lines, but otherwise is a perfect superset
90of '1t' format.
91
92If it is desired to recognize one from the other in a program, look at the
93"address" word (see below), where '1u' format adds a bus number. If 2 colons
94are present, it's the '1t' format, otherwise '1u'.
95
96Any text format data consists of a stream of events, such as URB submission,
Linus Torvalds1da177e2005-04-16 15:20:36 -070097URB callback, submission error. Every event is a text line, which consists
Pete Zaitcev6f23ee12006-12-30 22:43:10 -080098of whitespace separated words. The number or position of words may depend
Linus Torvalds1da177e2005-04-16 15:20:36 -070099on the event type, but there is a set of words, common for all types.
100
101Here is the list of words, from left to right:
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800102
Pete Zaitcevaacf4a02008-12-04 16:17:00 -0700103- URB Tag. This is used to identify URBs, and is normally an in-kernel address
104 of the URB structure in hexadecimal, but can be a sequence number or any
105 other unique string, within reason.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800106
Linus Torvalds1da177e2005-04-16 15:20:36 -0700107- Timestamp in microseconds, a decimal number. The timestamp's resolution
108 depends on available clock, and so it can be much worse than a microsecond
109 (if the implementation uses jiffies, for example).
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800110
Linus Torvalds1da177e2005-04-16 15:20:36 -0700111- Event Type. This type refers to the format of the event, not URB type.
112 Available types are: S - submission, C - callback, E - submission error.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800113
114- "Address" word (formerly a "pipe"). It consists of four fields, separated by
115 colons: URB type and direction, Bus number, Device address, Endpoint number.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700116 Type and direction are encoded with two bytes in the following manner:
117 Ci Co Control input and output
118 Zi Zo Isochronous input and output
119 Ii Io Interrupt input and output
120 Bi Bo Bulk input and output
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800121 Bus number, Device address, and Endpoint are decimal numbers, but they may
122 have leading zeros, for the sake of human readers.
123
124- URB Status word. This is either a letter, or several numbers separated
125 by colons: URB status, interval, start frame, and error count. Unlike the
126 "address" word, all fields save the status are optional. Interval is printed
127 only for interrupt and isochronous URBs. Start frame is printed only for
128 isochronous URBs. Error count is printed only for isochronous callback
129 events.
130
131 The status field is a decimal number, sometimes negative, which represents
132 a "status" field of the URB. This field makes no sense for submissions, but
133 is present anyway to help scripts with parsing. When an error occurs, the
134 field contains the error code.
135
136 In case of a submission of a Control packet, this field contains a Setup Tag
137 instead of an group of numbers. It is easy to tell whether the Setup Tag is
138 present because it is never a number. Thus if scripts find a set of numbers
139 in this word, they proceed to read Data Length (except for isochronous URBs).
140 If they find something else, like a letter, they read the setup packet before
141 reading the Data Length or isochronous descriptors.
142
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700143- Setup packet, if present, consists of 5 words: one of each for bmRequestType,
144 bRequest, wValue, wIndex, wLength, as specified by the USB Specification 2.0.
145 These words are safe to decode if Setup Tag was 's'. Otherwise, the setup
146 packet was present, but not captured, and the fields contain filler.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800147
148- Number of isochronous frame descriptors and descriptors themselves.
149 If an Isochronous transfer event has a set of descriptors, a total number
150 of them in an URB is printed first, then a word per descriptor, up to a
151 total of 5. The word consists of 3 colon-separated decimal numbers for
152 status, offset, and length respectively. For submissions, initial length
153 is reported. For callbacks, actual length is reported.
154
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -0700155- Data Length. For submissions, this is the requested length. For callbacks,
156 this is the actual length.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800157
Linus Torvalds1da177e2005-04-16 15:20:36 -0700158- Data tag. The usbmon may not always capture data, even if length is nonzero.
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -0700159 The data words are present only if this tag is '='.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800160
Linus Torvalds1da177e2005-04-16 15:20:36 -0700161- Data words follow, in big endian hexadecimal format. Notice that they are
162 not machine words, but really just a byte stream split into words to make
163 it easier to read. Thus, the last word may contain from one to four bytes.
164 The length of collected data is limited and can be less than the data length
165 report in Data Length word.
166
167Here is an example of code to read the data stream in a well known programming
168language:
169
170class ParsedLine {
171 int data_len; /* Available length of data */
172 byte data[];
173
174 void parseData(StringTokenizer st) {
175 int availwords = st.countTokens();
176 data = new byte[availwords * 4];
177 data_len = 0;
178 while (st.hasMoreTokens()) {
179 String data_str = st.nextToken();
180 int len = data_str.length() / 2;
181 int i;
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700182 int b; // byte is signed, apparently?! XXX
Linus Torvalds1da177e2005-04-16 15:20:36 -0700183 for (i = 0; i < len; i++) {
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700184 // data[data_len] = Byte.parseByte(
185 // data_str.substring(i*2, i*2 + 2),
186 // 16);
187 b = Integer.parseInt(
188 data_str.substring(i*2, i*2 + 2),
189 16);
190 if (b >= 128)
191 b *= -1;
192 data[data_len] = (byte) b;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700193 data_len++;
194 }
195 }
196 }
197}
198
Linus Torvalds1da177e2005-04-16 15:20:36 -0700199Examples:
200
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700201An input control transfer to get a port status.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700202
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800203d5ea89a0 3575914555 S Ci:1:001:0 s a3 00 0000 0003 0004 4 <
204d5ea89a0 3575914560 C Ci:1:001:0 0 4 = 01050000
Linus Torvalds1da177e2005-04-16 15:20:36 -0700205
206An output bulk transfer to send a SCSI command 0x5E in a 31-byte Bulk wrapper
207to a storage device at address 5:
208
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800209dd65f0e8 4128379752 S Bo:1:005:2 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000
210dd65f0e8 4128379808 C Bo:1:005:2 0 31 >
Linus Torvalds1da177e2005-04-16 15:20:36 -0700211
212* Raw binary format and API
213
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800214The overall architecture of the API is about the same as the one above,
215only the events are delivered in binary format. Each event is sent in
216the following structure (its name is made up, so that we can refer to it):
217
218struct usbmon_packet {
219 u64 id; /* 0: URB ID - from submission to callback */
220 unsigned char type; /* 8: Same as text; extensible. */
221 unsigned char xfer_type; /* ISO (0), Intr, Control, Bulk (3) */
222 unsigned char epnum; /* Endpoint number and transfer direction */
223 unsigned char devnum; /* Device address */
224 u16 busnum; /* 12: Bus number */
225 char flag_setup; /* 14: Same as text */
226 char flag_data; /* 15: Same as text; Binary zero is OK. */
227 s64 ts_sec; /* 16: gettimeofday */
228 s32 ts_usec; /* 24: gettimeofday */
229 int status; /* 28: */
230 unsigned int length; /* 32: Length of data (submitted or actual) */
231 unsigned int len_cap; /* 36: Delivered length */
232 unsigned char setup[8]; /* 40: Only for Control 'S' */
233}; /* 48 bytes total */
234
235These events can be received from a character device by reading with read(2),
236with an ioctl(2), or by accessing the buffer with mmap.
237
238The character device is usually called /dev/usbmonN, where N is the USB bus
239number. Number zero (/dev/usbmon0) is special and means "all buses".
240However, this feature is not implemented yet. Note that specific naming
241policy is set by your Linux distribution.
242
243If you create /dev/usbmon0 by hand, make sure that it is owned by root
244and has mode 0600. Otherwise, unpriviledged users will be able to snoop
245keyboard traffic.
246
247The following ioctl calls are available, with MON_IOC_MAGIC 0x92:
248
249 MON_IOCQ_URB_LEN, defined as _IO(MON_IOC_MAGIC, 1)
250
251This call returns the length of data in the next event. Note that majority of
252events contain no data, so if this call returns zero, it does not mean that
253no events are available.
254
255 MON_IOCG_STATS, defined as _IOR(MON_IOC_MAGIC, 3, struct mon_bin_stats)
256
257The argument is a pointer to the following structure:
258
259struct mon_bin_stats {
260 u32 queued;
261 u32 dropped;
262};
263
264The member "queued" refers to the number of events currently queued in the
265buffer (and not to the number of events processed since the last reset).
266
267The member "dropped" is the number of events lost since the last call
268to MON_IOCG_STATS.
269
270 MON_IOCT_RING_SIZE, defined as _IO(MON_IOC_MAGIC, 4)
271
272This call sets the buffer size. The argument is the size in bytes.
273The size may be rounded down to the next chunk (or page). If the requested
274size is out of [unspecified] bounds for this kernel, the call fails with
275-EINVAL.
276
277 MON_IOCQ_RING_SIZE, defined as _IO(MON_IOC_MAGIC, 5)
278
279This call returns the current size of the buffer in bytes.
280
281 MON_IOCX_GET, defined as _IOW(MON_IOC_MAGIC, 6, struct mon_get_arg)
282
283This call waits for events to arrive if none were in the kernel buffer,
284then returns the first event. Its argument is a pointer to the following
285structure:
286
287struct mon_get_arg {
288 struct usbmon_packet *hdr;
289 void *data;
290 size_t alloc; /* Length of data (can be zero) */
291};
292
293Before the call, hdr, data, and alloc should be filled. Upon return, the area
294pointed by hdr contains the next event structure, and the data buffer contains
295the data, if any. The event is removed from the kernel buffer.
296
297 MON_IOCX_MFETCH, defined as _IOWR(MON_IOC_MAGIC, 7, struct mon_mfetch_arg)
298
299This ioctl is primarily used when the application accesses the buffer
300with mmap(2). Its argument is a pointer to the following structure:
301
302struct mon_mfetch_arg {
303 uint32_t *offvec; /* Vector of events fetched */
304 uint32_t nfetch; /* Number of events to fetch (out: fetched) */
305 uint32_t nflush; /* Number of events to flush */
306};
307
308The ioctl operates in 3 stages.
309
310First, it removes and discards up to nflush events from the kernel buffer.
311The actual number of events discarded is returned in nflush.
312
313Second, it waits for an event to be present in the buffer, unless the pseudo-
314device is open with O_NONBLOCK.
315
316Third, it extracts up to nfetch offsets into the mmap buffer, and stores
317them into the offvec. The actual number of event offsets is stored into
318the nfetch.
319
320 MON_IOCH_MFLUSH, defined as _IO(MON_IOC_MAGIC, 8)
321
322This call removes a number of events from the kernel buffer. Its argument
323is the number of events to remove. If the buffer contains fewer events
324than requested, all events present are removed, and no error is reported.
325This works when no events are available too.
326
327 FIONBIO
328
329The ioctl FIONBIO may be implemented in the future, if there's a need.
330
331In addition to ioctl(2) and read(2), the special file of binary API can
332be polled with select(2) and poll(2). But lseek(2) does not work.
333
334* Memory-mapped access of the kernel buffer for the binary API
335
336The basic idea is simple:
337
338To prepare, map the buffer by getting the current size, then using mmap(2).
339Then, execute a loop similar to the one written in pseudo-code below:
340
341 struct mon_mfetch_arg fetch;
342 struct usbmon_packet *hdr;
343 int nflush = 0;
344 for (;;) {
345 fetch.offvec = vec; // Has N 32-bit words
346 fetch.nfetch = N; // Or less than N
347 fetch.nflush = nflush;
348 ioctl(fd, MON_IOCX_MFETCH, &fetch); // Process errors, too
349 nflush = fetch.nfetch; // This many packets to flush when done
350 for (i = 0; i < nflush; i++) {
351 hdr = (struct ubsmon_packet *) &mmap_area[vec[i]];
352 if (hdr->type == '@') // Filler packet
353 continue;
354 caddr_t data = &mmap_area[vec[i]] + 64;
355 process_packet(hdr, data);
356 }
357 }
358
359Thus, the main idea is to execute only one ioctl per N events.
360
361Although the buffer is circular, the returned headers and data do not cross
362the end of the buffer, so the above pseudo-code does not need any gathering.