--- /dev/null
+* 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.
+
+Two APIs are currently implemented: "text" and "binary". The binary API
+is available through a character device in /dev namespace and is an ABI.
+The text API is deprecated since 2.6.35, but available for convenience.
+
+* 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 more 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/usb/usbmon
+0s 0u 1s 1t 1u 2s 2t 2u 3s 3t 3u 4s 4t 4u
+#
+
+Now you can choose to either use the socket '0u' (to capture packets on all
+buses), and skip to step #3, or find the bus used by your device with step #2.
+This allows to filter away annoying devices that talk continuously.
+
+2. Find which bus connects to the desired device
+
+Run "cat /sys/kernel/debug/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 the two
+/sys/kernel/debug/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. Alternatively, you can look at the output from
+"lsusb" and get the bus number from the appropriate line. Example:
+
+Bus 003 Device 002: ID 0557:2004 ATEN UC100KM V2.00
+
+3. Start 'cat'
+
+# cat /sys/kernel/debug/usb/usbmon/3u > /tmp/1.mon.out
+
+to listen on a single bus, otherwise, to listen on all buses, type:
+
+# cat /sys/kernel/debug/usb/usbmon/0u > /tmp/1.mon.out
+
+This process will read until it is 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
+
+Two formats are supported currently: the original, or '1t' format, and
+the '1u' format. The '1t' format is deprecated in kernel 2.6.21. The '1u'
+format adds a few fields, such as ISO frame descriptors, interval, etc.
+It produces slightly longer lines, but otherwise is a perfect superset
+of '1t' format.
+
+If it is desired to recognize one from the other in a program, look at the
+"address" word (see below), where '1u' format adds a bus number. If 2 colons
+are present, it's the '1t' format, otherwise '1u'.
+
+Any text format 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, and is normally an in-kernel address
+ of the URB structure in hexadecimal, but can be a sequence number or any
+ other unique string, within reason.
+
+- 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.
+
+- "Address" word (formerly a "pipe"). It consists of four fields, separated by
+ colons: URB type and direction, Bus number, 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
+ Bus number, Device address, and Endpoint are decimal numbers, but they may
+ have leading zeros, for the sake of human readers.
+
+- URB Status word. This is either a letter, or several numbers separated
+ by colons: URB status, interval, start frame, and error count. Unlike the
+ "address" word, all fields save the status are optional. Interval is printed
+ only for interrupt and isochronous URBs. Start frame is printed only for
+ isochronous URBs. Error count is printed only for isochronous callback
+ events.
+
+ The status field is a decimal 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 group of numbers. It is easy to tell whether the Setup Tag is
+ present because it is never a number. Thus if scripts find a set of numbers
+ in this word, they proceed to read Data Length (except for isochronous URBs).
+ If they find something else, like a letter, they read the setup packet before
+ reading the Data Length or isochronous descriptors.
+
+- 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.
+
+- Number of isochronous frame descriptors and descriptors themselves.
+ If an Isochronous transfer event has a set of descriptors, a total number
+ of them in an URB is printed first, then a word per descriptor, up to a
+ total of 5. The word consists of 3 colon-separated decimal numbers for
+ status, offset, and length respectively. For submissions, initial length
+ is reported. For callbacks, actual length is reported.
+
+- 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
+ reported in the Data Length word. In the case of an Isochronous input (Zi)
+ completion where the received data is sparse in the buffer, the length of
+ the collected data can be greater than the Data Length value (because Data
+ Length counts only the bytes that were received whereas the Data words
+ contain the entire transfer buffer).
+
+Examples:
+
+An input control transfer to get a port status.
+
+d5ea89a0 3575914555 S Ci:1:001:0 s a3 00 0000 0003 0004 4 <
+d5ea89a0 3575914560 C Ci:1:001:0 0 4 = 01050000
+
+An output bulk transfer to send a SCSI command 0x28 (READ_10) in a 31-byte
+Bulk wrapper to a storage device at address 5:
+
+dd65f0e8 4128379752 S Bo:1:005:2 -115 31 = 55534243 ad000000 00800000 80010a28 20000000 20000040 00000000 000000
+dd65f0e8 4128379808 C Bo:1:005:2 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 */
+ union { /* 40: */
+ unsigned char setup[SETUP_LEN]; /* Only for Control S-type */
+ struct iso_rec { /* Only for ISO */
+ int error_count;
+ int numdesc;
+ } iso;
+ } s;
+ int interval; /* 48: Only for Interrupt and ISO */
+ int start_frame; /* 52: For ISO */
+ unsigned int xfer_flags; /* 56: copy of URB's transfer_flags */
+ unsigned int ndesc; /* 60: Actual number of ISO descriptors */
+}; /* 64 total length */
+
+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. However, read(2)
+only returns first 48 bytes for compatibility reasons.
+
+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".
+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, unprivileged 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)
+ MON_IOCX_GETX, defined as _IOW(MON_IOC_MAGIC, 10, struct mon_get_arg)
+
+These calls wait for events to arrive if none were in the kernel buffer,
+then return the first event. The 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.
+
+The MON_IOCX_GET copies 48 bytes to hdr area, MON_IOCX_GETX copies 64 bytes.
+
+ 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.
Code Review / kvmfornfv.git / blobdiff