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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
50Run "cat /proc/bus/usb/devices", and find the T-line which corresponds to
51the device. Usually you do it by looking for the vendor string. If you have
52many similar devices, unplug one and compare two /proc/bus/usb/devices outputs.
53The T-line will have a bus number. Example:
54
55T: Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 0
56D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
57P: Vendor=0557 ProdID=2004 Rev= 1.00
58S: Manufacturer=ATEN
59S: Product=UC100KM V2.00
60
61Bus=03 means it's bus 3.
62
633. Start 'cat'
64
Rogério Britof0cc82a2009-08-22 17:33:53 -030065# cat /sys/kernel/debug/usb/usbmon/3u > /tmp/1.mon.out
Linus Torvalds1da177e2005-04-16 15:20:36 -070066
Paolo 'Blaisorblade' Giarrusso092a2122007-08-24 12:19:22 +020067to listen on a single bus, otherwise, to listen on all buses, type:
68
Rogério Britof0cc82a2009-08-22 17:33:53 -030069# cat /sys/kernel/debug/usb/usbmon/0u > /tmp/1.mon.out
Paolo 'Blaisorblade' Giarrusso092a2122007-08-24 12:19:22 +020070
Linus Torvalds1da177e2005-04-16 15:20:36 -070071This process will be reading until killed. Naturally, the output can be
72redirected to a desirable location. This is preferred, because it is going
73to be quite long.
74
754. Perform the desired operation on the USB bus
76
77This is where you do something that creates the traffic: plug in a flash key,
78copy files, control a webcam, etc.
79
805. Kill cat
81
82Usually it's done with a keyboard interrupt (Control-C).
83
84At this point the output file (/tmp/1.mon.out in this example) can be saved,
85sent by e-mail, or inspected with a text editor. In the last case make sure
86that the file size is not excessive for your favourite editor.
87
88* Raw text data format
89
Pete Zaitcevf1c9e302007-02-24 19:27:33 -080090Two formats are supported currently: the original, or '1t' format, and
91the '1u' format. The '1t' format is deprecated in kernel 2.6.21. The '1u'
92format adds a few fields, such as ISO frame descriptors, interval, etc.
93It produces slightly longer lines, but otherwise is a perfect superset
94of '1t' format.
95
96If it is desired to recognize one from the other in a program, look at the
97"address" word (see below), where '1u' format adds a bus number. If 2 colons
98are present, it's the '1t' format, otherwise '1u'.
99
100Any text format data consists of a stream of events, such as URB submission,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700101URB callback, submission error. Every event is a text line, which consists
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800102of whitespace separated words. The number or position of words may depend
Linus Torvalds1da177e2005-04-16 15:20:36 -0700103on the event type, but there is a set of words, common for all types.
104
105Here is the list of words, from left to right:
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800106
Pete Zaitcevaacf4a02008-12-04 16:17:00 -0700107- URB Tag. This is used to identify URBs, and is normally an in-kernel address
108 of the URB structure in hexadecimal, but can be a sequence number or any
109 other unique string, within reason.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800110
Linus Torvalds1da177e2005-04-16 15:20:36 -0700111- Timestamp in microseconds, a decimal number. The timestamp's resolution
112 depends on available clock, and so it can be much worse than a microsecond
113 (if the implementation uses jiffies, for example).
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800114
Linus Torvalds1da177e2005-04-16 15:20:36 -0700115- Event Type. This type refers to the format of the event, not URB type.
116 Available types are: S - submission, C - callback, E - submission error.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800117
118- "Address" word (formerly a "pipe"). It consists of four fields, separated by
119 colons: URB type and direction, Bus number, Device address, Endpoint number.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700120 Type and direction are encoded with two bytes in the following manner:
121 Ci Co Control input and output
122 Zi Zo Isochronous input and output
123 Ii Io Interrupt input and output
124 Bi Bo Bulk input and output
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800125 Bus number, Device address, and Endpoint are decimal numbers, but they may
126 have leading zeros, for the sake of human readers.
127
128- URB Status word. This is either a letter, or several numbers separated
129 by colons: URB status, interval, start frame, and error count. Unlike the
130 "address" word, all fields save the status are optional. Interval is printed
131 only for interrupt and isochronous URBs. Start frame is printed only for
132 isochronous URBs. Error count is printed only for isochronous callback
133 events.
134
135 The status field is a decimal number, sometimes negative, which represents
136 a "status" field of the URB. This field makes no sense for submissions, but
137 is present anyway to help scripts with parsing. When an error occurs, the
138 field contains the error code.
139
140 In case of a submission of a Control packet, this field contains a Setup Tag
141 instead of an group of numbers. It is easy to tell whether the Setup Tag is
142 present because it is never a number. Thus if scripts find a set of numbers
143 in this word, they proceed to read Data Length (except for isochronous URBs).
144 If they find something else, like a letter, they read the setup packet before
145 reading the Data Length or isochronous descriptors.
146
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700147- Setup packet, if present, consists of 5 words: one of each for bmRequestType,
148 bRequest, wValue, wIndex, wLength, as specified by the USB Specification 2.0.
149 These words are safe to decode if Setup Tag was 's'. Otherwise, the setup
150 packet was present, but not captured, and the fields contain filler.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800151
152- Number of isochronous frame descriptors and descriptors themselves.
153 If an Isochronous transfer event has a set of descriptors, a total number
154 of them in an URB is printed first, then a word per descriptor, up to a
155 total of 5. The word consists of 3 colon-separated decimal numbers for
156 status, offset, and length respectively. For submissions, initial length
157 is reported. For callbacks, actual length is reported.
158
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -0700159- Data Length. For submissions, this is the requested length. For callbacks,
160 this is the actual length.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800161
Linus Torvalds1da177e2005-04-16 15:20:36 -0700162- Data tag. The usbmon may not always capture data, even if length is nonzero.
Pete Zaitcevd9ac2cf2006-06-12 20:09:39 -0700163 The data words are present only if this tag is '='.
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800164
Linus Torvalds1da177e2005-04-16 15:20:36 -0700165- Data words follow, in big endian hexadecimal format. Notice that they are
166 not machine words, but really just a byte stream split into words to make
167 it easier to read. Thus, the last word may contain from one to four bytes.
168 The length of collected data is limited and can be less than the data length
Pete Zaitcevd25bc4d2011-02-03 22:01:36 -0700169 reported in the Data Length word. In the case of an Isochronous input (Zi)
170 completion where the received data is sparse in the buffer, the length of
171 the collected data can be greater than the Data Length value (because Data
172 Length counts only the bytes that were received whereas the Data words
173 contain the entire transfer buffer).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700174
Linus Torvalds1da177e2005-04-16 15:20:36 -0700175Examples:
176
Pete Zaitcevae0d6cc2005-06-25 14:32:59 -0700177An input control transfer to get a port status.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700178
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800179d5ea89a0 3575914555 S Ci:1:001:0 s a3 00 0000 0003 0004 4 <
180d5ea89a0 3575914560 C Ci:1:001:0 0 4 = 01050000
Linus Torvalds1da177e2005-04-16 15:20:36 -0700181
182An output bulk transfer to send a SCSI command 0x5E in a 31-byte Bulk wrapper
183to a storage device at address 5:
184
Pete Zaitcevf1c9e302007-02-24 19:27:33 -0800185dd65f0e8 4128379752 S Bo:1:005:2 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000
186dd65f0e8 4128379808 C Bo:1:005:2 0 31 >
Linus Torvalds1da177e2005-04-16 15:20:36 -0700187
188* Raw binary format and API
189
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800190The overall architecture of the API is about the same as the one above,
191only the events are delivered in binary format. Each event is sent in
192the following structure (its name is made up, so that we can refer to it):
193
194struct usbmon_packet {
195 u64 id; /* 0: URB ID - from submission to callback */
196 unsigned char type; /* 8: Same as text; extensible. */
197 unsigned char xfer_type; /* ISO (0), Intr, Control, Bulk (3) */
198 unsigned char epnum; /* Endpoint number and transfer direction */
199 unsigned char devnum; /* Device address */
200 u16 busnum; /* 12: Bus number */
201 char flag_setup; /* 14: Same as text */
202 char flag_data; /* 15: Same as text; Binary zero is OK. */
203 s64 ts_sec; /* 16: gettimeofday */
204 s32 ts_usec; /* 24: gettimeofday */
205 int status; /* 28: */
206 unsigned int length; /* 32: Length of data (submitted or actual) */
207 unsigned int len_cap; /* 36: Delivered length */
Pete Zaitcev471c6042009-02-19 22:54:45 -0700208 union { /* 40: */
209 unsigned char setup[SETUP_LEN]; /* Only for Control S-type */
210 struct iso_rec { /* Only for ISO */
211 int error_count;
212 int numdesc;
213 } iso;
214 } s;
215 int interval; /* 48: Only for Interrupt and ISO */
216 int start_frame; /* 52: For ISO */
217 unsigned int xfer_flags; /* 56: copy of URB's transfer_flags */
218 unsigned int ndesc; /* 60: Actual number of ISO descriptors */
219}; /* 64 total length */
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800220
221These events can be received from a character device by reading with read(2),
Pete Zaitcev471c6042009-02-19 22:54:45 -0700222with an ioctl(2), or by accessing the buffer with mmap. However, read(2)
223only returns first 48 bytes for compatibility reasons.
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800224
225The character device is usually called /dev/usbmonN, where N is the USB bus
226number. Number zero (/dev/usbmon0) is special and means "all buses".
Pete Zaitcev471c6042009-02-19 22:54:45 -0700227Note that specific naming policy is set by your Linux distribution.
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800228
229If you create /dev/usbmon0 by hand, make sure that it is owned by root
230and has mode 0600. Otherwise, unpriviledged users will be able to snoop
231keyboard traffic.
232
233The following ioctl calls are available, with MON_IOC_MAGIC 0x92:
234
235 MON_IOCQ_URB_LEN, defined as _IO(MON_IOC_MAGIC, 1)
236
237This call returns the length of data in the next event. Note that majority of
238events contain no data, so if this call returns zero, it does not mean that
239no events are available.
240
241 MON_IOCG_STATS, defined as _IOR(MON_IOC_MAGIC, 3, struct mon_bin_stats)
242
243The argument is a pointer to the following structure:
244
245struct mon_bin_stats {
246 u32 queued;
247 u32 dropped;
248};
249
250The member "queued" refers to the number of events currently queued in the
251buffer (and not to the number of events processed since the last reset).
252
253The member "dropped" is the number of events lost since the last call
254to MON_IOCG_STATS.
255
256 MON_IOCT_RING_SIZE, defined as _IO(MON_IOC_MAGIC, 4)
257
258This call sets the buffer size. The argument is the size in bytes.
259The size may be rounded down to the next chunk (or page). If the requested
260size is out of [unspecified] bounds for this kernel, the call fails with
261-EINVAL.
262
263 MON_IOCQ_RING_SIZE, defined as _IO(MON_IOC_MAGIC, 5)
264
265This call returns the current size of the buffer in bytes.
266
267 MON_IOCX_GET, defined as _IOW(MON_IOC_MAGIC, 6, struct mon_get_arg)
Pete Zaitcev471c6042009-02-19 22:54:45 -0700268 MON_IOCX_GETX, defined as _IOW(MON_IOC_MAGIC, 10, struct mon_get_arg)
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800269
Pete Zaitcev471c6042009-02-19 22:54:45 -0700270These calls wait for events to arrive if none were in the kernel buffer,
271then return the first event. The argument is a pointer to the following
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800272structure:
273
274struct mon_get_arg {
275 struct usbmon_packet *hdr;
276 void *data;
277 size_t alloc; /* Length of data (can be zero) */
278};
279
280Before the call, hdr, data, and alloc should be filled. Upon return, the area
281pointed by hdr contains the next event structure, and the data buffer contains
282the data, if any. The event is removed from the kernel buffer.
283
Pete Zaitcevf4e23322009-06-10 15:23:52 -0600284The MON_IOCX_GET copies 48 bytes to hdr area, MON_IOCX_GETX copies 64 bytes.
Pete Zaitcev471c6042009-02-19 22:54:45 -0700285
Pete Zaitcev6f23ee12006-12-30 22:43:10 -0800286 MON_IOCX_MFETCH, defined as _IOWR(MON_IOC_MAGIC, 7, struct mon_mfetch_arg)
287
288This ioctl is primarily used when the application accesses the buffer
289with mmap(2). Its argument is a pointer to the following structure:
290
291struct mon_mfetch_arg {
292 uint32_t *offvec; /* Vector of events fetched */
293 uint32_t nfetch; /* Number of events to fetch (out: fetched) */
294 uint32_t nflush; /* Number of events to flush */
295};
296
297The ioctl operates in 3 stages.
298
299First, it removes and discards up to nflush events from the kernel buffer.
300The actual number of events discarded is returned in nflush.
301
302Second, it waits for an event to be present in the buffer, unless the pseudo-
303device is open with O_NONBLOCK.
304
305Third, it extracts up to nfetch offsets into the mmap buffer, and stores
306them into the offvec. The actual number of event offsets is stored into
307the nfetch.
308
309 MON_IOCH_MFLUSH, defined as _IO(MON_IOC_MAGIC, 8)
310
311This call removes a number of events from the kernel buffer. Its argument
312is the number of events to remove. If the buffer contains fewer events
313than requested, all events present are removed, and no error is reported.
314This works when no events are available too.
315
316 FIONBIO
317
318The ioctl FIONBIO may be implemented in the future, if there's a need.
319
320In addition to ioctl(2) and read(2), the special file of binary API can
321be polled with select(2) and poll(2). But lseek(2) does not work.
322
323* Memory-mapped access of the kernel buffer for the binary API
324
325The basic idea is simple:
326
327To prepare, map the buffer by getting the current size, then using mmap(2).
328Then, execute a loop similar to the one written in pseudo-code below:
329
330 struct mon_mfetch_arg fetch;
331 struct usbmon_packet *hdr;
332 int nflush = 0;
333 for (;;) {
334 fetch.offvec = vec; // Has N 32-bit words
335 fetch.nfetch = N; // Or less than N
336 fetch.nflush = nflush;
337 ioctl(fd, MON_IOCX_MFETCH, &fetch); // Process errors, too
338 nflush = fetch.nfetch; // This many packets to flush when done
339 for (i = 0; i < nflush; i++) {
340 hdr = (struct ubsmon_packet *) &mmap_area[vec[i]];
341 if (hdr->type == '@') // Filler packet
342 continue;
343 caddr_t data = &mmap_area[vec[i]] + 64;
344 process_packet(hdr, data);
345 }
346 }
347
348Thus, the main idea is to execute only one ioctl per N events.
349
350Although the buffer is circular, the returned headers and data do not cross
351the end of the buffer, so the above pseudo-code does not need any gathering.