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1 | * Introduction |
2 | ||
3 | The name "usbmon" in lowercase refers to a facility in kernel which is | |
4 | used to collect traces of I/O on the USB bus. This function is analogous | |
5 | to a packet socket used by network monitoring tools such as tcpdump(1) | |
6 | or Ethereal. Similarly, it is expected that a tool such as usbdump or | |
7 | USBMon (with uppercase letters) is used to examine raw traces produced | |
8 | by usbmon. | |
9 | ||
10 | The usbmon reports requests made by peripheral-specific drivers to Host | |
11 | Controller Drivers (HCD). So, if HCD is buggy, the traces reported by | |
12 | usbmon may not correspond to bus transactions precisely. This is the same | |
13 | situation as with tcpdump. | |
14 | ||
15 | * How to use usbmon to collect raw text traces | |
16 | ||
17 | Unlike the packet socket, usbmon has an interface which provides traces | |
18 | in a text format. This is used for two purposes. First, it serves as a | |
f1c9e30b | 19 | common trace exchange format for tools while more sophisticated formats |
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20 | are finalized. Second, humans can read it in case tools are not available. |
21 | ||
22 | To collect a raw text trace, execute following steps. | |
23 | ||
24 | 1. Prepare | |
25 | ||
26 | Mount debugfs (it has to be enabled in your kernel configuration), and | |
27 | load the usbmon module (if built as module). The second step is skipped | |
28 | if usbmon is built into the kernel. | |
29 | ||
30 | # mount -t debugfs none_debugs /sys/kernel/debug | |
31 | # modprobe usbmon | |
d9ac2cfc | 32 | # |
1da177e4 LT |
33 | |
34 | Verify that bus sockets are present. | |
35 | ||
d9ac2cfc | 36 | # ls /sys/kernel/debug/usbmon |
092a212e | 37 | 0s 0t 0u 1s 1t 1u 2s 2t 2u 3s 3t 3u 4s 4t 4u |
d9ac2cfc | 38 | # |
1da177e4 | 39 | |
092a212e PBG |
40 | Now you can choose to either use the sockets numbered '0' (to capture packets on |
41 | all buses), and skip to step #3, or find the bus used by your device with step #2. | |
42 | ||
1da177e4 LT |
43 | 2. Find which bus connects to the desired device |
44 | ||
45 | Run "cat /proc/bus/usb/devices", and find the T-line which corresponds to | |
46 | the device. Usually you do it by looking for the vendor string. If you have | |
47 | many similar devices, unplug one and compare two /proc/bus/usb/devices outputs. | |
48 | The T-line will have a bus number. Example: | |
49 | ||
50 | T: Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 0 | |
51 | D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1 | |
52 | P: Vendor=0557 ProdID=2004 Rev= 1.00 | |
53 | S: Manufacturer=ATEN | |
54 | S: Product=UC100KM V2.00 | |
55 | ||
56 | Bus=03 means it's bus 3. | |
57 | ||
58 | 3. Start 'cat' | |
59 | ||
f1c9e30b | 60 | # cat /sys/kernel/debug/usbmon/3u > /tmp/1.mon.out |
1da177e4 | 61 | |
092a212e PBG |
62 | to listen on a single bus, otherwise, to listen on all buses, type: |
63 | ||
64 | # cat /sys/kernel/debug/usbmon/0u > /tmp/1.mon.out | |
65 | ||
1da177e4 LT |
66 | This process will be reading until killed. Naturally, the output can be |
67 | redirected to a desirable location. This is preferred, because it is going | |
68 | to be quite long. | |
69 | ||
70 | 4. Perform the desired operation on the USB bus | |
71 | ||
72 | This is where you do something that creates the traffic: plug in a flash key, | |
73 | copy files, control a webcam, etc. | |
74 | ||
75 | 5. Kill cat | |
76 | ||
77 | Usually it's done with a keyboard interrupt (Control-C). | |
78 | ||
79 | At this point the output file (/tmp/1.mon.out in this example) can be saved, | |
80 | sent by e-mail, or inspected with a text editor. In the last case make sure | |
81 | that the file size is not excessive for your favourite editor. | |
82 | ||
83 | * Raw text data format | |
84 | ||
f1c9e30b PZ |
85 | Two formats are supported currently: the original, or '1t' format, and |
86 | the '1u' format. The '1t' format is deprecated in kernel 2.6.21. The '1u' | |
87 | format adds a few fields, such as ISO frame descriptors, interval, etc. | |
88 | It produces slightly longer lines, but otherwise is a perfect superset | |
89 | of '1t' format. | |
90 | ||
91 | If it is desired to recognize one from the other in a program, look at the | |
92 | "address" word (see below), where '1u' format adds a bus number. If 2 colons | |
93 | are present, it's the '1t' format, otherwise '1u'. | |
94 | ||
95 | Any text format data consists of a stream of events, such as URB submission, | |
1da177e4 | 96 | URB callback, submission error. Every event is a text line, which consists |
6f23ee1f | 97 | of whitespace separated words. The number or position of words may depend |
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98 | on the event type, but there is a set of words, common for all types. |
99 | ||
100 | Here is the list of words, from left to right: | |
f1c9e30b | 101 | |
1da177e4 LT |
102 | - URB Tag. This is used to identify URBs is normally a kernel mode address |
103 | of the URB structure in hexadecimal. | |
f1c9e30b | 104 | |
1da177e4 LT |
105 | - Timestamp in microseconds, a decimal number. The timestamp's resolution |
106 | depends on available clock, and so it can be much worse than a microsecond | |
107 | (if the implementation uses jiffies, for example). | |
f1c9e30b | 108 | |
1da177e4 LT |
109 | - Event Type. This type refers to the format of the event, not URB type. |
110 | Available types are: S - submission, C - callback, E - submission error. | |
f1c9e30b PZ |
111 | |
112 | - "Address" word (formerly a "pipe"). It consists of four fields, separated by | |
113 | colons: URB type and direction, Bus number, Device address, Endpoint number. | |
1da177e4 LT |
114 | Type and direction are encoded with two bytes in the following manner: |
115 | Ci Co Control input and output | |
116 | Zi Zo Isochronous input and output | |
117 | Ii Io Interrupt input and output | |
118 | Bi Bo Bulk input and output | |
f1c9e30b PZ |
119 | Bus number, Device address, and Endpoint are decimal numbers, but they may |
120 | have leading zeros, for the sake of human readers. | |
121 | ||
122 | - URB Status word. This is either a letter, or several numbers separated | |
123 | by colons: URB status, interval, start frame, and error count. Unlike the | |
124 | "address" word, all fields save the status are optional. Interval is printed | |
125 | only for interrupt and isochronous URBs. Start frame is printed only for | |
126 | isochronous URBs. Error count is printed only for isochronous callback | |
127 | events. | |
128 | ||
129 | The status field is a decimal number, sometimes negative, which represents | |
130 | a "status" field of the URB. This field makes no sense for submissions, but | |
131 | is present anyway to help scripts with parsing. When an error occurs, the | |
132 | field contains the error code. | |
133 | ||
134 | In case of a submission of a Control packet, this field contains a Setup Tag | |
135 | instead of an group of numbers. It is easy to tell whether the Setup Tag is | |
136 | present because it is never a number. Thus if scripts find a set of numbers | |
137 | in this word, they proceed to read Data Length (except for isochronous URBs). | |
138 | If they find something else, like a letter, they read the setup packet before | |
139 | reading the Data Length or isochronous descriptors. | |
140 | ||
ae0d6cce PZ |
141 | - Setup packet, if present, consists of 5 words: one of each for bmRequestType, |
142 | bRequest, wValue, wIndex, wLength, as specified by the USB Specification 2.0. | |
143 | These words are safe to decode if Setup Tag was 's'. Otherwise, the setup | |
144 | packet was present, but not captured, and the fields contain filler. | |
f1c9e30b PZ |
145 | |
146 | - Number of isochronous frame descriptors and descriptors themselves. | |
147 | If an Isochronous transfer event has a set of descriptors, a total number | |
148 | of them in an URB is printed first, then a word per descriptor, up to a | |
149 | total of 5. The word consists of 3 colon-separated decimal numbers for | |
150 | status, offset, and length respectively. For submissions, initial length | |
151 | is reported. For callbacks, actual length is reported. | |
152 | ||
d9ac2cfc PZ |
153 | - Data Length. For submissions, this is the requested length. For callbacks, |
154 | this is the actual length. | |
f1c9e30b | 155 | |
1da177e4 | 156 | - Data tag. The usbmon may not always capture data, even if length is nonzero. |
d9ac2cfc | 157 | The data words are present only if this tag is '='. |
f1c9e30b | 158 | |
1da177e4 LT |
159 | - Data words follow, in big endian hexadecimal format. Notice that they are |
160 | not machine words, but really just a byte stream split into words to make | |
161 | it easier to read. Thus, the last word may contain from one to four bytes. | |
162 | The length of collected data is limited and can be less than the data length | |
163 | report in Data Length word. | |
164 | ||
165 | Here is an example of code to read the data stream in a well known programming | |
166 | language: | |
167 | ||
168 | class ParsedLine { | |
169 | int data_len; /* Available length of data */ | |
170 | byte data[]; | |
171 | ||
172 | void parseData(StringTokenizer st) { | |
173 | int availwords = st.countTokens(); | |
174 | data = new byte[availwords * 4]; | |
175 | data_len = 0; | |
176 | while (st.hasMoreTokens()) { | |
177 | String data_str = st.nextToken(); | |
178 | int len = data_str.length() / 2; | |
179 | int i; | |
ae0d6cce | 180 | int b; // byte is signed, apparently?! XXX |
1da177e4 | 181 | for (i = 0; i < len; i++) { |
ae0d6cce PZ |
182 | // data[data_len] = Byte.parseByte( |
183 | // data_str.substring(i*2, i*2 + 2), | |
184 | // 16); | |
185 | b = Integer.parseInt( | |
186 | data_str.substring(i*2, i*2 + 2), | |
187 | 16); | |
188 | if (b >= 128) | |
189 | b *= -1; | |
190 | data[data_len] = (byte) b; | |
1da177e4 LT |
191 | data_len++; |
192 | } | |
193 | } | |
194 | } | |
195 | } | |
196 | ||
1da177e4 LT |
197 | Examples: |
198 | ||
ae0d6cce | 199 | An input control transfer to get a port status. |
1da177e4 | 200 | |
f1c9e30b PZ |
201 | d5ea89a0 3575914555 S Ci:1:001:0 s a3 00 0000 0003 0004 4 < |
202 | d5ea89a0 3575914560 C Ci:1:001:0 0 4 = 01050000 | |
1da177e4 LT |
203 | |
204 | An output bulk transfer to send a SCSI command 0x5E in a 31-byte Bulk wrapper | |
205 | to a storage device at address 5: | |
206 | ||
f1c9e30b PZ |
207 | dd65f0e8 4128379752 S Bo:1:005:2 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000 |
208 | dd65f0e8 4128379808 C Bo:1:005:2 0 31 > | |
1da177e4 LT |
209 | |
210 | * Raw binary format and API | |
211 | ||
6f23ee1f PZ |
212 | The overall architecture of the API is about the same as the one above, |
213 | only the events are delivered in binary format. Each event is sent in | |
214 | the following structure (its name is made up, so that we can refer to it): | |
215 | ||
216 | struct usbmon_packet { | |
217 | u64 id; /* 0: URB ID - from submission to callback */ | |
218 | unsigned char type; /* 8: Same as text; extensible. */ | |
219 | unsigned char xfer_type; /* ISO (0), Intr, Control, Bulk (3) */ | |
220 | unsigned char epnum; /* Endpoint number and transfer direction */ | |
221 | unsigned char devnum; /* Device address */ | |
222 | u16 busnum; /* 12: Bus number */ | |
223 | char flag_setup; /* 14: Same as text */ | |
224 | char flag_data; /* 15: Same as text; Binary zero is OK. */ | |
225 | s64 ts_sec; /* 16: gettimeofday */ | |
226 | s32 ts_usec; /* 24: gettimeofday */ | |
227 | int status; /* 28: */ | |
228 | unsigned int length; /* 32: Length of data (submitted or actual) */ | |
229 | unsigned int len_cap; /* 36: Delivered length */ | |
230 | unsigned char setup[8]; /* 40: Only for Control 'S' */ | |
231 | }; /* 48 bytes total */ | |
232 | ||
233 | These events can be received from a character device by reading with read(2), | |
234 | with an ioctl(2), or by accessing the buffer with mmap. | |
235 | ||
236 | The character device is usually called /dev/usbmonN, where N is the USB bus | |
237 | number. Number zero (/dev/usbmon0) is special and means "all buses". | |
238 | However, this feature is not implemented yet. Note that specific naming | |
239 | policy is set by your Linux distribution. | |
240 | ||
241 | If you create /dev/usbmon0 by hand, make sure that it is owned by root | |
242 | and has mode 0600. Otherwise, unpriviledged users will be able to snoop | |
243 | keyboard traffic. | |
244 | ||
245 | The following ioctl calls are available, with MON_IOC_MAGIC 0x92: | |
246 | ||
247 | MON_IOCQ_URB_LEN, defined as _IO(MON_IOC_MAGIC, 1) | |
248 | ||
249 | This call returns the length of data in the next event. Note that majority of | |
250 | events contain no data, so if this call returns zero, it does not mean that | |
251 | no events are available. | |
252 | ||
253 | MON_IOCG_STATS, defined as _IOR(MON_IOC_MAGIC, 3, struct mon_bin_stats) | |
254 | ||
255 | The argument is a pointer to the following structure: | |
256 | ||
257 | struct mon_bin_stats { | |
258 | u32 queued; | |
259 | u32 dropped; | |
260 | }; | |
261 | ||
262 | The member "queued" refers to the number of events currently queued in the | |
263 | buffer (and not to the number of events processed since the last reset). | |
264 | ||
265 | The member "dropped" is the number of events lost since the last call | |
266 | to MON_IOCG_STATS. | |
267 | ||
268 | MON_IOCT_RING_SIZE, defined as _IO(MON_IOC_MAGIC, 4) | |
269 | ||
270 | This call sets the buffer size. The argument is the size in bytes. | |
271 | The size may be rounded down to the next chunk (or page). If the requested | |
272 | size is out of [unspecified] bounds for this kernel, the call fails with | |
273 | -EINVAL. | |
274 | ||
275 | MON_IOCQ_RING_SIZE, defined as _IO(MON_IOC_MAGIC, 5) | |
276 | ||
277 | This call returns the current size of the buffer in bytes. | |
278 | ||
279 | MON_IOCX_GET, defined as _IOW(MON_IOC_MAGIC, 6, struct mon_get_arg) | |
280 | ||
281 | This call waits for events to arrive if none were in the kernel buffer, | |
282 | then returns the first event. Its argument is a pointer to the following | |
283 | structure: | |
284 | ||
285 | struct mon_get_arg { | |
286 | struct usbmon_packet *hdr; | |
287 | void *data; | |
288 | size_t alloc; /* Length of data (can be zero) */ | |
289 | }; | |
290 | ||
291 | Before the call, hdr, data, and alloc should be filled. Upon return, the area | |
292 | pointed by hdr contains the next event structure, and the data buffer contains | |
293 | the data, if any. The event is removed from the kernel buffer. | |
294 | ||
295 | MON_IOCX_MFETCH, defined as _IOWR(MON_IOC_MAGIC, 7, struct mon_mfetch_arg) | |
296 | ||
297 | This ioctl is primarily used when the application accesses the buffer | |
298 | with mmap(2). Its argument is a pointer to the following structure: | |
299 | ||
300 | struct mon_mfetch_arg { | |
301 | uint32_t *offvec; /* Vector of events fetched */ | |
302 | uint32_t nfetch; /* Number of events to fetch (out: fetched) */ | |
303 | uint32_t nflush; /* Number of events to flush */ | |
304 | }; | |
305 | ||
306 | The ioctl operates in 3 stages. | |
307 | ||
308 | First, it removes and discards up to nflush events from the kernel buffer. | |
309 | The actual number of events discarded is returned in nflush. | |
310 | ||
311 | Second, it waits for an event to be present in the buffer, unless the pseudo- | |
312 | device is open with O_NONBLOCK. | |
313 | ||
314 | Third, it extracts up to nfetch offsets into the mmap buffer, and stores | |
315 | them into the offvec. The actual number of event offsets is stored into | |
316 | the nfetch. | |
317 | ||
318 | MON_IOCH_MFLUSH, defined as _IO(MON_IOC_MAGIC, 8) | |
319 | ||
320 | This call removes a number of events from the kernel buffer. Its argument | |
321 | is the number of events to remove. If the buffer contains fewer events | |
322 | than requested, all events present are removed, and no error is reported. | |
323 | This works when no events are available too. | |
324 | ||
325 | FIONBIO | |
326 | ||
327 | The ioctl FIONBIO may be implemented in the future, if there's a need. | |
328 | ||
329 | In addition to ioctl(2) and read(2), the special file of binary API can | |
330 | be polled with select(2) and poll(2). But lseek(2) does not work. | |
331 | ||
332 | * Memory-mapped access of the kernel buffer for the binary API | |
333 | ||
334 | The basic idea is simple: | |
335 | ||
336 | To prepare, map the buffer by getting the current size, then using mmap(2). | |
337 | Then, execute a loop similar to the one written in pseudo-code below: | |
338 | ||
339 | struct mon_mfetch_arg fetch; | |
340 | struct usbmon_packet *hdr; | |
341 | int nflush = 0; | |
342 | for (;;) { | |
343 | fetch.offvec = vec; // Has N 32-bit words | |
344 | fetch.nfetch = N; // Or less than N | |
345 | fetch.nflush = nflush; | |
346 | ioctl(fd, MON_IOCX_MFETCH, &fetch); // Process errors, too | |
347 | nflush = fetch.nfetch; // This many packets to flush when done | |
348 | for (i = 0; i < nflush; i++) { | |
349 | hdr = (struct ubsmon_packet *) &mmap_area[vec[i]]; | |
350 | if (hdr->type == '@') // Filler packet | |
351 | continue; | |
352 | caddr_t data = &mmap_area[vec[i]] + 64; | |
353 | process_packet(hdr, data); | |
354 | } | |
355 | } | |
356 | ||
357 | Thus, the main idea is to execute only one ioctl per N events. | |
358 | ||
359 | Although the buffer is circular, the returned headers and data do not cross | |
360 | the end of the buffer, so the above pseudo-code does not need any gathering. |