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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
Pete Zaitcevd25bc4d2011-02-03 22:01:36 -070015Two APIs are currently implemented: "text" and "binary". The binary API
16is available through a character device in /dev namespace and is an ABI.
17The text API is deprecated since 2.6.35, but available for convenience.
18
Linus Torvalds1da177e2005-04-16 15:20:36 -070019* How to use usbmon to collect raw text traces
20
21Unlike the packet socket, usbmon has an interface which provides traces
22in a text format. This is used for two purposes. First, it serves as a
Pete Zaitcevf1c9e302007-02-24 19:27:33 -080023common trace exchange format for tools while more sophisticated formats
Linus Torvalds1da177e2005-04-16 15:20:36 -070024are finalized. Second, humans can read it in case tools are not available.
25
26To collect a raw text trace, execute following steps.
27
281. Prepare
29
30Mount debugfs (it has to be enabled in your kernel configuration), and
31load the usbmon module (if built as module). The second step is skipped
32if usbmon is built into the kernel.
33
34# mount -t debugfs none_debugs /sys/kernel/debug
35# modprobe usbmon
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -070036#
Linus Torvalds1da177e2005-04-16 15:20:36 -070037
38Verify that bus sockets are present.
39
Rogério Britof0cc82a2009-08-22 17:33:53 -030040# ls /sys/kernel/debug/usb/usbmon
Pete Zaitcevaacf4a02008-12-04 16:17:00 -0700410s 0u 1s 1t 1u 2s 2t 2u 3s 3t 3u 4s 4t 4u
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -070042#
Linus Torvalds1da177e2005-04-16 15:20:36 -070043
Pete Zaitcevaacf4a02008-12-04 16:17:00 -070044Now you can choose to either use the socket '0u' (to capture packets on all
45buses), and skip to step #3, or find the bus used by your device with step #2.
46This allows to filter away annoying devices that talk continuously.
Paolo 'Blaisorblade' Giarrusso092a2122007-08-24 12:19:22 +020047
Linus Torvalds1da177e2005-04-16 15:20:36 -0700482. Find which bus connects to the desired device
49
Alan Sternd8cae982012-01-04 16:36:35 -050050Run "cat /sys/kernel/debug/usb/devices", and find the T-line which corresponds
51to the device. Usually you do it by looking for the vendor string. If you have
52many similar devices, unplug one and compare the two
53/sys/kernel/debug/usb/devices outputs. The T-line will have a bus number.
54Example:
Linus Torvalds1da177e2005-04-16 15:20:36 -070055
56T: Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 0
57D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
58P: Vendor=0557 ProdID=2004 Rev= 1.00
59S: Manufacturer=ATEN
60S: Product=UC100KM V2.00
61
Alan Sternd8cae982012-01-04 16:36:35 -050062"Bus=03" means it's bus 3. Alternatively, you can look at the output from
63"lsusb" and get the bus number from the appropriate line. Example:
64
65Bus 003 Device 002: ID 0557:2004 ATEN UC100KM V2.00
Linus Torvalds1da177e2005-04-16 15:20:36 -070066
673. Start 'cat'
68
Rogério Britof0cc82a2009-08-22 17:33:53 -030069# cat /sys/kernel/debug/usb/usbmon/3u > /tmp/1.mon.out
Linus Torvalds1da177e2005-04-16 15:20:36 -070070
Paolo 'Blaisorblade' Giarrusso092a2122007-08-24 12:19:22 +020071to listen on a single bus, otherwise, to listen on all buses, type:
72
Rogério Britof0cc82a2009-08-22 17:33:53 -030073# cat /sys/kernel/debug/usb/usbmon/0u > /tmp/1.mon.out
Paolo 'Blaisorblade' Giarrusso092a2122007-08-24 12:19:22 +020074
Jeremiah Mahler76900372014-12-21 05:29:20 -080075This process will read until it is killed. Naturally, the output can be
Linus Torvalds1da177e2005-04-16 15:20:36 -070076redirected to a desirable location. This is preferred, because it is going
77to be quite long.
78
794. Perform the desired operation on the USB bus
80
81This is where you do something that creates the traffic: plug in a flash key,
82copy files, control a webcam, etc.
83
845. Kill cat
85
86Usually it's done with a keyboard interrupt (Control-C).
87
88At this point the output file (/tmp/1.mon.out in this example) can be saved,
89sent by e-mail, or inspected with a text editor. In the last case make sure
90that the file size is not excessive for your favourite editor.
91
92* Raw text data format
93
Pete Zaitcevf1c9e302007-02-24 19:27:33 -080094Two formats are supported currently: the original, or '1t' format, and
95the '1u' format. The '1t' format is deprecated in kernel 2.6.21. The '1u'
96format adds a few fields, such as ISO frame descriptors, interval, etc.
97It produces slightly longer lines, but otherwise is a perfect superset
98of '1t' format.
99
100If it is desired to recognize one from the other in a program, look at the
101"address" word (see below), where '1u' format adds a bus number. If 2 colons
102are present, it's the '1t' format, otherwise '1u'.
103
104Any text format data consists of a stream of events, such as URB submission,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700105URB callback, submission error. Every event is a text line, which consists
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800106of whitespace separated words. The number or position of words may depend
Linus Torvalds1da177e2005-04-16 15:20:36 -0700107on the event type, but there is a set of words, common for all types.
108
109Here is the list of words, from left to right:
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800110
Pete Zaitcevaacf4a02008-12-04 16:17:00 -0700111- URB Tag. This is used to identify URBs, and is normally an in-kernel address
112 of the URB structure in hexadecimal, but can be a sequence number or any
113 other unique string, within reason.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800114
Linus Torvalds1da177e2005-04-16 15:20:36 -0700115- Timestamp in microseconds, a decimal number. The timestamp's resolution
116 depends on available clock, and so it can be much worse than a microsecond
117 (if the implementation uses jiffies, for example).
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800118
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119- Event Type. This type refers to the format of the event, not URB type.
120 Available types are: S - submission, C - callback, E - submission error.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800121
122- "Address" word (formerly a "pipe"). It consists of four fields, separated by
123 colons: URB type and direction, Bus number, Device address, Endpoint number.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700124 Type and direction are encoded with two bytes in the following manner:
125 Ci Co Control input and output
126 Zi Zo Isochronous input and output
127 Ii Io Interrupt input and output
128 Bi Bo Bulk input and output
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800129 Bus number, Device address, and Endpoint are decimal numbers, but they may
130 have leading zeros, for the sake of human readers.
131
132- URB Status word. This is either a letter, or several numbers separated
133 by colons: URB status, interval, start frame, and error count. Unlike the
134 "address" word, all fields save the status are optional. Interval is printed
135 only for interrupt and isochronous URBs. Start frame is printed only for
136 isochronous URBs. Error count is printed only for isochronous callback
137 events.
138
139 The status field is a decimal number, sometimes negative, which represents
140 a "status" field of the URB. This field makes no sense for submissions, but
141 is present anyway to help scripts with parsing. When an error occurs, the
142 field contains the error code.
143
144 In case of a submission of a Control packet, this field contains a Setup Tag
145 instead of an group of numbers. It is easy to tell whether the Setup Tag is
146 present because it is never a number. Thus if scripts find a set of numbers
147 in this word, they proceed to read Data Length (except for isochronous URBs).
148 If they find something else, like a letter, they read the setup packet before
149 reading the Data Length or isochronous descriptors.
150
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700151- Setup packet, if present, consists of 5 words: one of each for bmRequestType,
152 bRequest, wValue, wIndex, wLength, as specified by the USB Specification 2.0.
153 These words are safe to decode if Setup Tag was 's'. Otherwise, the setup
154 packet was present, but not captured, and the fields contain filler.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800155
156- Number of isochronous frame descriptors and descriptors themselves.
157 If an Isochronous transfer event has a set of descriptors, a total number
158 of them in an URB is printed first, then a word per descriptor, up to a
159 total of 5. The word consists of 3 colon-separated decimal numbers for
160 status, offset, and length respectively. For submissions, initial length
161 is reported. For callbacks, actual length is reported.
162
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -0700163- Data Length. For submissions, this is the requested length. For callbacks,
164 this is the actual length.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800165
Linus Torvalds1da177e2005-04-16 15:20:36 -0700166- Data tag. The usbmon may not always capture data, even if length is nonzero.
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -0700167 The data words are present only if this tag is '='.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800168
Linus Torvalds1da177e2005-04-16 15:20:36 -0700169- Data words follow, in big endian hexadecimal format. Notice that they are
170 not machine words, but really just a byte stream split into words to make
171 it easier to read. Thus, the last word may contain from one to four bytes.
172 The length of collected data is limited and can be less than the data length
Pete Zaitcevd25bc4d2011-02-03 22:01:36 -0700173 reported in the Data Length word. In the case of an Isochronous input (Zi)
174 completion where the received data is sparse in the buffer, the length of
175 the collected data can be greater than the Data Length value (because Data
176 Length counts only the bytes that were received whereas the Data words
177 contain the entire transfer buffer).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700178
Linus Torvalds1da177e2005-04-16 15:20:36 -0700179Examples:
180
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700181An input control transfer to get a port status.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700182
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800183d5ea89a0 3575914555 S Ci:1:001:0 s a3 00 0000 0003 0004 4 <
184d5ea89a0 3575914560 C Ci:1:001:0 0 4 = 01050000
Linus Torvalds1da177e2005-04-16 15:20:36 -0700185
Sebastian Andrzej Siewior2e8dc2f2012-03-17 15:23:49 +0100186An output bulk transfer to send a SCSI command 0x28 (READ_10) in a 31-byte
187Bulk wrapper to a storage device at address 5:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700188
Sebastian Andrzej Siewior2e8dc2f2012-03-17 15:23:49 +0100189dd65f0e8 4128379752 S Bo:1:005:2 -115 31 = 55534243 ad000000 00800000 80010a28 20000000 20000040 00000000 000000
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800190dd65f0e8 4128379808 C Bo:1:005:2 0 31 >
Linus Torvalds1da177e2005-04-16 15:20:36 -0700191
192* Raw binary format and API
193
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800194The overall architecture of the API is about the same as the one above,
195only the events are delivered in binary format. Each event is sent in
196the following structure (its name is made up, so that we can refer to it):
197
198struct usbmon_packet {
199 u64 id; /* 0: URB ID - from submission to callback */
200 unsigned char type; /* 8: Same as text; extensible. */
201 unsigned char xfer_type; /* ISO (0), Intr, Control, Bulk (3) */
202 unsigned char epnum; /* Endpoint number and transfer direction */
203 unsigned char devnum; /* Device address */
204 u16 busnum; /* 12: Bus number */
205 char flag_setup; /* 14: Same as text */
206 char flag_data; /* 15: Same as text; Binary zero is OK. */
207 s64 ts_sec; /* 16: gettimeofday */
208 s32 ts_usec; /* 24: gettimeofday */
209 int status; /* 28: */
210 unsigned int length; /* 32: Length of data (submitted or actual) */
211 unsigned int len_cap; /* 36: Delivered length */
Pete Zaitcev471c6042009-02-19 22:54:45 -0700212 union { /* 40: */
213 unsigned char setup[SETUP_LEN]; /* Only for Control S-type */
214 struct iso_rec { /* Only for ISO */
215 int error_count;
216 int numdesc;
217 } iso;
218 } s;
219 int interval; /* 48: Only for Interrupt and ISO */
220 int start_frame; /* 52: For ISO */
221 unsigned int xfer_flags; /* 56: copy of URB's transfer_flags */
222 unsigned int ndesc; /* 60: Actual number of ISO descriptors */
223}; /* 64 total length */
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800224
225These events can be received from a character device by reading with read(2),
Pete Zaitcev471c6042009-02-19 22:54:45 -0700226with an ioctl(2), or by accessing the buffer with mmap. However, read(2)
227only returns first 48 bytes for compatibility reasons.
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800228
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".
Pete Zaitcev471c6042009-02-19 22:54:45 -0700231Note that specific naming policy is set by your Linux distribution.
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800232
233If you create /dev/usbmon0 by hand, make sure that it is owned by root
Jeremiah Mahler11a63222014-12-21 05:30:04 -0800234and has mode 0600. Otherwise, unprivileged users will be able to snoop
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800235keyboard traffic.
236
237The following ioctl calls are available, with MON_IOC_MAGIC 0x92:
238
239 MON_IOCQ_URB_LEN, defined as _IO(MON_IOC_MAGIC, 1)
240
241This call returns the length of data in the next event. Note that majority of
242events contain no data, so if this call returns zero, it does not mean that
243no events are available.
244
245 MON_IOCG_STATS, defined as _IOR(MON_IOC_MAGIC, 3, struct mon_bin_stats)
246
247The argument is a pointer to the following structure:
248
249struct mon_bin_stats {
250 u32 queued;
251 u32 dropped;
252};
253
254The member "queued" refers to the number of events currently queued in the
255buffer (and not to the number of events processed since the last reset).
256
257The member "dropped" is the number of events lost since the last call
258to MON_IOCG_STATS.
259
260 MON_IOCT_RING_SIZE, defined as _IO(MON_IOC_MAGIC, 4)
261
262This call sets the buffer size. The argument is the size in bytes.
263The size may be rounded down to the next chunk (or page). If the requested
264size is out of [unspecified] bounds for this kernel, the call fails with
265-EINVAL.
266
267 MON_IOCQ_RING_SIZE, defined as _IO(MON_IOC_MAGIC, 5)
268
269This call returns the current size of the buffer in bytes.
270
271 MON_IOCX_GET, defined as _IOW(MON_IOC_MAGIC, 6, struct mon_get_arg)
Pete Zaitcev471c6042009-02-19 22:54:45 -0700272 MON_IOCX_GETX, defined as _IOW(MON_IOC_MAGIC, 10, struct mon_get_arg)
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800273
Pete Zaitcev471c6042009-02-19 22:54:45 -0700274These calls wait for events to arrive if none were in the kernel buffer,
275then return the first event. The argument is a pointer to the following
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800276structure:
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
Pete Zaitcevf4e23322009-06-10 15:23:52 -0600288The MON_IOCX_GET copies 48 bytes to hdr area, MON_IOCX_GETX copies 64 bytes.
Pete Zaitcev471c6042009-02-19 22:54:45 -0700289
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800290 MON_IOCX_MFETCH, defined as _IOWR(MON_IOC_MAGIC, 7, struct mon_mfetch_arg)
291
292This ioctl is primarily used when the application accesses the buffer
293with mmap(2). Its argument is a pointer to the following structure:
294
295struct mon_mfetch_arg {
296 uint32_t *offvec; /* Vector of events fetched */
297 uint32_t nfetch; /* Number of events to fetch (out: fetched) */
298 uint32_t nflush; /* Number of events to flush */
299};
300
301The ioctl operates in 3 stages.
302
303First, it removes and discards up to nflush events from the kernel buffer.
304The actual number of events discarded is returned in nflush.
305
306Second, it waits for an event to be present in the buffer, unless the pseudo-
307device is open with O_NONBLOCK.
308
309Third, it extracts up to nfetch offsets into the mmap buffer, and stores
310them into the offvec. The actual number of event offsets is stored into
311the nfetch.
312
313 MON_IOCH_MFLUSH, defined as _IO(MON_IOC_MAGIC, 8)
314
315This call removes a number of events from the kernel buffer. Its argument
316is the number of events to remove. If the buffer contains fewer events
317than requested, all events present are removed, and no error is reported.
318This works when no events are available too.
319
320 FIONBIO
321
322The ioctl FIONBIO may be implemented in the future, if there's a need.
323
324In addition to ioctl(2) and read(2), the special file of binary API can
325be polled with select(2) and poll(2). But lseek(2) does not work.
326
327* Memory-mapped access of the kernel buffer for the binary API
328
329The basic idea is simple:
330
331To prepare, map the buffer by getting the current size, then using mmap(2).
332Then, execute a loop similar to the one written in pseudo-code below:
333
334 struct mon_mfetch_arg fetch;
335 struct usbmon_packet *hdr;
336 int nflush = 0;
337 for (;;) {
338 fetch.offvec = vec; // Has N 32-bit words
339 fetch.nfetch = N; // Or less than N
340 fetch.nflush = nflush;
341 ioctl(fd, MON_IOCX_MFETCH, &fetch); // Process errors, too
342 nflush = fetch.nfetch; // This many packets to flush when done
343 for (i = 0; i < nflush; i++) {
344 hdr = (struct ubsmon_packet *) &mmap_area[vec[i]];
345 if (hdr->type == '@') // Filler packet
346 continue;
347 caddr_t data = &mmap_area[vec[i]] + 64;
348 process_packet(hdr, data);
349 }
350 }
351
352Thus, the main idea is to execute only one ioctl per N events.
353
354Although the buffer is circular, the returned headers and data do not cross
355the end of the buffer, so the above pseudo-code does not need any gathering.