You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
321 lines
12 KiB
321 lines
12 KiB
* Introduction
|
|
|
|
The name "usbmon" in lowercase refers to a facility in kernel which is
|
|
used to collect traces of I/O on the USB bus. This function is analogous
|
|
to a packet socket used by network monitoring tools such as tcpdump(1)
|
|
or Ethereal. Similarly, it is expected that a tool such as usbdump or
|
|
USBMon (with uppercase letters) is used to examine raw traces produced
|
|
by usbmon.
|
|
|
|
The usbmon reports requests made by peripheral-specific drivers to Host
|
|
Controller Drivers (HCD). So, if HCD is buggy, the traces reported by
|
|
usbmon may not correspond to bus transactions precisely. This is the same
|
|
situation as with tcpdump.
|
|
|
|
* How to use usbmon to collect raw text traces
|
|
|
|
Unlike the packet socket, usbmon has an interface which provides traces
|
|
in a text format. This is used for two purposes. First, it serves as a
|
|
common trace exchange format for tools while most sophisticated formats
|
|
are finalized. Second, humans can read it in case tools are not available.
|
|
|
|
To collect a raw text trace, execute following steps.
|
|
|
|
1. Prepare
|
|
|
|
Mount debugfs (it has to be enabled in your kernel configuration), and
|
|
load the usbmon module (if built as module). The second step is skipped
|
|
if usbmon is built into the kernel.
|
|
|
|
# mount -t debugfs none_debugs /sys/kernel/debug
|
|
# modprobe usbmon
|
|
#
|
|
|
|
Verify that bus sockets are present.
|
|
|
|
# ls /sys/kernel/debug/usbmon
|
|
1s 1t 2s 2t 3s 3t 4s 4t
|
|
#
|
|
|
|
2. Find which bus connects to the desired device
|
|
|
|
Run "cat /proc/bus/usb/devices", and find the T-line which corresponds to
|
|
the device. Usually you do it by looking for the vendor string. If you have
|
|
many similar devices, unplug one and compare two /proc/bus/usb/devices outputs.
|
|
The T-line will have a bus number. Example:
|
|
|
|
T: Bus=03 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 0
|
|
D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
|
|
P: Vendor=0557 ProdID=2004 Rev= 1.00
|
|
S: Manufacturer=ATEN
|
|
S: Product=UC100KM V2.00
|
|
|
|
Bus=03 means it's bus 3.
|
|
|
|
3. Start 'cat'
|
|
|
|
# cat /sys/kernel/debug/usbmon/3t > /tmp/1.mon.out
|
|
|
|
This process will be reading until killed. Naturally, the output can be
|
|
redirected to a desirable location. This is preferred, because it is going
|
|
to be quite long.
|
|
|
|
4. Perform the desired operation on the USB bus
|
|
|
|
This is where you do something that creates the traffic: plug in a flash key,
|
|
copy files, control a webcam, etc.
|
|
|
|
5. Kill cat
|
|
|
|
Usually it's done with a keyboard interrupt (Control-C).
|
|
|
|
At this point the output file (/tmp/1.mon.out in this example) can be saved,
|
|
sent by e-mail, or inspected with a text editor. In the last case make sure
|
|
that the file size is not excessive for your favourite editor.
|
|
|
|
* Raw text data format
|
|
|
|
The '1t' type data consists of a stream of events, such as URB submission,
|
|
URB callback, submission error. Every event is a text line, which consists
|
|
of whitespace separated words. The number or position of words may depend
|
|
on the event type, but there is a set of words, common for all types.
|
|
|
|
Here is the list of words, from left to right:
|
|
- URB Tag. This is used to identify URBs is normally a kernel mode address
|
|
of the URB structure in hexadecimal.
|
|
- Timestamp in microseconds, a decimal number. The timestamp's resolution
|
|
depends on available clock, and so it can be much worse than a microsecond
|
|
(if the implementation uses jiffies, for example).
|
|
- Event Type. This type refers to the format of the event, not URB type.
|
|
Available types are: S - submission, C - callback, E - submission error.
|
|
- "Pipe". The pipe concept is deprecated. This is a composite word, used to
|
|
be derived from information in pipes. It consists of three fields, separated
|
|
by colons: URB type and direction, Device address, Endpoint number.
|
|
Type and direction are encoded with two bytes in the following manner:
|
|
Ci Co Control input and output
|
|
Zi Zo Isochronous input and output
|
|
Ii Io Interrupt input and output
|
|
Bi Bo Bulk input and output
|
|
Device address and Endpoint number are 3-digit and 2-digit (respectively)
|
|
decimal numbers, with leading zeroes.
|
|
- URB Status. In most cases, this field contains a number, sometimes negative,
|
|
which represents a "status" field of the URB. This field makes no sense for
|
|
submissions, but is present anyway to help scripts with parsing. When an
|
|
error occurs, the field contains the error code. In case of a submission of
|
|
a Control packet, this field contains a Setup Tag instead of an error code.
|
|
It is easy to tell whether the Setup Tag is present because it is never a
|
|
number. Thus if scripts find a number in this field, they proceed to read
|
|
Data Length. If they find something else, like a letter, they read the setup
|
|
packet before reading the Data Length.
|
|
- Setup packet, if present, consists of 5 words: one of each for bmRequestType,
|
|
bRequest, wValue, wIndex, wLength, as specified by the USB Specification 2.0.
|
|
These words are safe to decode if Setup Tag was 's'. Otherwise, the setup
|
|
packet was present, but not captured, and the fields contain filler.
|
|
- Data Length. For submissions, this is the requested length. For callbacks,
|
|
this is the actual length.
|
|
- Data tag. The usbmon may not always capture data, even if length is nonzero.
|
|
The data words are present only if this tag is '='.
|
|
- Data words follow, in big endian hexadecimal format. Notice that they are
|
|
not machine words, but really just a byte stream split into words to make
|
|
it easier to read. Thus, the last word may contain from one to four bytes.
|
|
The length of collected data is limited and can be less than the data length
|
|
report in Data Length word.
|
|
|
|
Here is an example of code to read the data stream in a well known programming
|
|
language:
|
|
|
|
class ParsedLine {
|
|
int data_len; /* Available length of data */
|
|
byte data[];
|
|
|
|
void parseData(StringTokenizer st) {
|
|
int availwords = st.countTokens();
|
|
data = new byte[availwords * 4];
|
|
data_len = 0;
|
|
while (st.hasMoreTokens()) {
|
|
String data_str = st.nextToken();
|
|
int len = data_str.length() / 2;
|
|
int i;
|
|
int b; // byte is signed, apparently?! XXX
|
|
for (i = 0; i < len; i++) {
|
|
// data[data_len] = Byte.parseByte(
|
|
// data_str.substring(i*2, i*2 + 2),
|
|
// 16);
|
|
b = Integer.parseInt(
|
|
data_str.substring(i*2, i*2 + 2),
|
|
16);
|
|
if (b >= 128)
|
|
b *= -1;
|
|
data[data_len] = (byte) b;
|
|
data_len++;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
This format may be changed in the future.
|
|
|
|
Examples:
|
|
|
|
An input control transfer to get a port status.
|
|
|
|
d5ea89a0 3575914555 S Ci:001:00 s a3 00 0000 0003 0004 4 <
|
|
d5ea89a0 3575914560 C Ci:001:00 0 4 = 01050000
|
|
|
|
An output bulk transfer to send a SCSI command 0x5E in a 31-byte Bulk wrapper
|
|
to a storage device at address 5:
|
|
|
|
dd65f0e8 4128379752 S Bo:005:02 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000
|
|
dd65f0e8 4128379808 C Bo:005:02 0 31 >
|
|
|
|
* Raw binary format and API
|
|
|
|
The overall architecture of the API is about the same as the one above,
|
|
only the events are delivered in binary format. Each event is sent in
|
|
the following structure (its name is made up, so that we can refer to it):
|
|
|
|
struct usbmon_packet {
|
|
u64 id; /* 0: URB ID - from submission to callback */
|
|
unsigned char type; /* 8: Same as text; extensible. */
|
|
unsigned char xfer_type; /* ISO (0), Intr, Control, Bulk (3) */
|
|
unsigned char epnum; /* Endpoint number and transfer direction */
|
|
unsigned char devnum; /* Device address */
|
|
u16 busnum; /* 12: Bus number */
|
|
char flag_setup; /* 14: Same as text */
|
|
char flag_data; /* 15: Same as text; Binary zero is OK. */
|
|
s64 ts_sec; /* 16: gettimeofday */
|
|
s32 ts_usec; /* 24: gettimeofday */
|
|
int status; /* 28: */
|
|
unsigned int length; /* 32: Length of data (submitted or actual) */
|
|
unsigned int len_cap; /* 36: Delivered length */
|
|
unsigned char setup[8]; /* 40: Only for Control 'S' */
|
|
}; /* 48 bytes total */
|
|
|
|
These events can be received from a character device by reading with read(2),
|
|
with an ioctl(2), or by accessing the buffer with mmap.
|
|
|
|
The character device is usually called /dev/usbmonN, where N is the USB bus
|
|
number. Number zero (/dev/usbmon0) is special and means "all buses".
|
|
However, this feature is not implemented yet. Note that specific naming
|
|
policy is set by your Linux distribution.
|
|
|
|
If you create /dev/usbmon0 by hand, make sure that it is owned by root
|
|
and has mode 0600. Otherwise, unpriviledged users will be able to snoop
|
|
keyboard traffic.
|
|
|
|
The following ioctl calls are available, with MON_IOC_MAGIC 0x92:
|
|
|
|
MON_IOCQ_URB_LEN, defined as _IO(MON_IOC_MAGIC, 1)
|
|
|
|
This call returns the length of data in the next event. Note that majority of
|
|
events contain no data, so if this call returns zero, it does not mean that
|
|
no events are available.
|
|
|
|
MON_IOCG_STATS, defined as _IOR(MON_IOC_MAGIC, 3, struct mon_bin_stats)
|
|
|
|
The argument is a pointer to the following structure:
|
|
|
|
struct mon_bin_stats {
|
|
u32 queued;
|
|
u32 dropped;
|
|
};
|
|
|
|
The member "queued" refers to the number of events currently queued in the
|
|
buffer (and not to the number of events processed since the last reset).
|
|
|
|
The member "dropped" is the number of events lost since the last call
|
|
to MON_IOCG_STATS.
|
|
|
|
MON_IOCT_RING_SIZE, defined as _IO(MON_IOC_MAGIC, 4)
|
|
|
|
This call sets the buffer size. The argument is the size in bytes.
|
|
The size may be rounded down to the next chunk (or page). If the requested
|
|
size is out of [unspecified] bounds for this kernel, the call fails with
|
|
-EINVAL.
|
|
|
|
MON_IOCQ_RING_SIZE, defined as _IO(MON_IOC_MAGIC, 5)
|
|
|
|
This call returns the current size of the buffer in bytes.
|
|
|
|
MON_IOCX_GET, defined as _IOW(MON_IOC_MAGIC, 6, struct mon_get_arg)
|
|
|
|
This call waits for events to arrive if none were in the kernel buffer,
|
|
then returns the first event. Its argument is a pointer to the following
|
|
structure:
|
|
|
|
struct mon_get_arg {
|
|
struct usbmon_packet *hdr;
|
|
void *data;
|
|
size_t alloc; /* Length of data (can be zero) */
|
|
};
|
|
|
|
Before the call, hdr, data, and alloc should be filled. Upon return, the area
|
|
pointed by hdr contains the next event structure, and the data buffer contains
|
|
the data, if any. The event is removed from the kernel buffer.
|
|
|
|
MON_IOCX_MFETCH, defined as _IOWR(MON_IOC_MAGIC, 7, struct mon_mfetch_arg)
|
|
|
|
This ioctl is primarily used when the application accesses the buffer
|
|
with mmap(2). Its argument is a pointer to the following structure:
|
|
|
|
struct mon_mfetch_arg {
|
|
uint32_t *offvec; /* Vector of events fetched */
|
|
uint32_t nfetch; /* Number of events to fetch (out: fetched) */
|
|
uint32_t nflush; /* Number of events to flush */
|
|
};
|
|
|
|
The ioctl operates in 3 stages.
|
|
|
|
First, it removes and discards up to nflush events from the kernel buffer.
|
|
The actual number of events discarded is returned in nflush.
|
|
|
|
Second, it waits for an event to be present in the buffer, unless the pseudo-
|
|
device is open with O_NONBLOCK.
|
|
|
|
Third, it extracts up to nfetch offsets into the mmap buffer, and stores
|
|
them into the offvec. The actual number of event offsets is stored into
|
|
the nfetch.
|
|
|
|
MON_IOCH_MFLUSH, defined as _IO(MON_IOC_MAGIC, 8)
|
|
|
|
This call removes a number of events from the kernel buffer. Its argument
|
|
is the number of events to remove. If the buffer contains fewer events
|
|
than requested, all events present are removed, and no error is reported.
|
|
This works when no events are available too.
|
|
|
|
FIONBIO
|
|
|
|
The ioctl FIONBIO may be implemented in the future, if there's a need.
|
|
|
|
In addition to ioctl(2) and read(2), the special file of binary API can
|
|
be polled with select(2) and poll(2). But lseek(2) does not work.
|
|
|
|
* Memory-mapped access of the kernel buffer for the binary API
|
|
|
|
The basic idea is simple:
|
|
|
|
To prepare, map the buffer by getting the current size, then using mmap(2).
|
|
Then, execute a loop similar to the one written in pseudo-code below:
|
|
|
|
struct mon_mfetch_arg fetch;
|
|
struct usbmon_packet *hdr;
|
|
int nflush = 0;
|
|
for (;;) {
|
|
fetch.offvec = vec; // Has N 32-bit words
|
|
fetch.nfetch = N; // Or less than N
|
|
fetch.nflush = nflush;
|
|
ioctl(fd, MON_IOCX_MFETCH, &fetch); // Process errors, too
|
|
nflush = fetch.nfetch; // This many packets to flush when done
|
|
for (i = 0; i < nflush; i++) {
|
|
hdr = (struct ubsmon_packet *) &mmap_area[vec[i]];
|
|
if (hdr->type == '@') // Filler packet
|
|
continue;
|
|
caddr_t data = &mmap_area[vec[i]] + 64;
|
|
process_packet(hdr, data);
|
|
}
|
|
}
|
|
|
|
Thus, the main idea is to execute only one ioctl per N events.
|
|
|
|
Although the buffer is circular, the returned headers and data do not cross
|
|
the end of the buffer, so the above pseudo-code does not need any gathering.
|
|
|