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
+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.
Verify that bus sockets are present.
# ls /sys/kernel/debug/usbmon
-1s 1t 2s 2t 3s 3t 4s 4t
+1s 1t 1u 2s 2t 2u 3s 3t 3u 4s 4t 4u
#
2. Find which bus connects to the desired device
3. Start 'cat'
-# cat /sys/kernel/debug/usbmon/3t > /tmp/1.mon.out
+# cat /sys/kernel/debug/usbmon/3u > /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
* Raw text data format
-The '1t' type data consists of a stream of events, such as URB submission,
+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 of position of words may depend
+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.
+
+- "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
- 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.
+ 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.
}
}
-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
+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 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 >
+dd65f0e8 4128379752 S Bo:1:005:2 -115 31 = 55534243 5e000000 00000000 00000600 00000000 00000000 00000000 000000
+dd65f0e8 4128379808 C Bo:1:005:2 0 31 >
* Raw binary format and API
-TBD
+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.
projects / linux-drm-fsl-dcu.git / blobdiff