[PATCH, RFC] USBIP protocol documentation

Németh Márton
2011-06-28T06:55:20Z

From: Márton Németh <nm127@freemail.hu>

USBIP v1.0.0 protocol documentation.

Signed-off-by: Márton Németh <nm127@freemail.hu>
---

Hi,

I tried to document the USBIP protocol as implemented in the Linux kernel 3.0-rc2.

The description is a preliminary draft only, it may contain mistakes. I tried
to document what I have understand from the source code and from the actual
captured network traffic when the USBIP is in action. Please review it, correct it,
point out the missing parts.

During I have documented the protocol a question came into my mind: why do we
have two different type of package when the URB completition handler is called,
namely USB_RET_SUBMIT and USBIP_RET_UNLINK? As far as I can see this causes race
condition because for one URB the completition handler is only called once. If
the one URB is sent in with USB_CMD_SUBMIT and then unlinked with USB_CMD_UNLINK
the completition handler is called only once. In the protocol, however, we have
two different type of packets: USB_RET_SUBMIT and USBIP_RET_UNLINK. The status
field of these messages may contain anything in this case depending on the timing.

Regards,

Márton Németh
---
diff -uprN staging-2.6.orig/drivers/staging/usbip/usbip_protocol.txt staging-2.6/drivers/staging/usbip/usbip_protocol.txt
--- staging-2.6.orig/drivers/staging/usbip/usbip_protocol.txt 1970-01-01 01:00:00.000000000 +0100
+++ staging-2.6/drivers/staging/usbip/usbip_protocol.txt 2011-06-28 08:30:04.000000000 +0200
@@ -0,0 +1,352 @@
+PRELIMINARY DRAFT, MAY CONTAIN MISTAKES!
+28 Jun 2011
+
+The USB/IP protocol follows a server/client architecture. The server exports the
+USB devices and the clients imports them. The device driver for the exported
+USB device runs on the client machine.
+
+The client may ask for the list of the exported USB devices. To get the list the
+client opens a TCP/IP connection towards the server, and sends an OP_REQ_DEVLIST
+packet on top of the TCP/IP connection (so the actual OP_REQ_DEVLIST may be sent
+in one or more pieces at the low level transport layer). The server sends back
+the OP_REP_DEVLIST packet which lists the exported USB devices. Finally the
+TCP/IP connection is closed.
+
+ virtual host controller usb host
+ "client" "server"
+ (imports USB devices) (exports USB devices)
+ | |
+ | OP_REQ_DEVLIST |
+ | ----------------------------------------------> |
+ | |
+ | OP_REP_DEVLIST |
+ | <---------------------------------------------- |
+ | |
+
+Once the client knows the list of exported USB devices it may decide to use one
+of them. First the client opens a TCP/IP connection towards the server and
+sends an OP_REQ_IMPORT packet. The server replies with OP_REP_IMPORT. If the
+import was successful the TCP/IP connection remains open and will be used
+to trasfer the URB traffic between the client and the server. The client may
+send two types of packets: the USBIP_CMD_SUBMIT to submit an URB, and
+USBIP_CMD_UNLINK to unlink a previously submitted URB. The answers of the
+server may be USBIP_RET_SUBMIT and USBIP_RET_UNLINK respectively.
+
+ virtual host controller usb host
+ "client" "server"
+ (imports USB devices) (exports USB devices)
+ | |
+ | OP_REQ_IMPORT |
+ | ----------------------------------------------> |
+ | |
+ | OP_REP_IMPORT |
+ | <---------------------------------------------- |
+ | |
+ | |
+ | USBIP_CMD_SUBMIT(seqnum = n) |
+ | ----------------------------------------------> |
+ | |
+ | USBIP_RET_SUBMIT(seqnum = n) |
+ | <---------------------------------------------- |
+ | . |
+ | : |
+ | |
+ | USBIP_CMD_SUBMIT(seqnum = m) |
+ | ----------------------------------------------> |
+ | |
+ | USBIP_CMD_SUBMIT(seqnum = m+1) |
+ | ----------------------------------------------> |
+ | |
+ | USBIP_CMD_SUBMIT(seqnum = m+2) |
+ | ----------------------------------------------> |
+ | |
+ | USBIP_RET_SUBMIT(seqnum = m) |
+ | <---------------------------------------------- |
+ | |
+ | USBIP_CMD_SUBMIT(seqnum = m+3) |
+ | ----------------------------------------------> |
+ | |
+ | USBIP_RET_SUBMIT(seqnum = m+1) |
+ | <---------------------------------------------- |
+ | |
+ | USBIP_CMD_SUBMIT(seqnum = m+4) |
+ | ----------------------------------------------> |
+ | |
+ | USBIP_RET_SUBMIT(seqnum = m+2) |
+ | <---------------------------------------------- |
+ | . |
+ | : |
+ | |
+ | USBIP_CMD_UNLINK |
+ | ----------------------------------------------> |
+ | |
+ | USBIP_RET_UNLINK |
+ | <---------------------------------------------- |
+ | |
+
+The fields are in network (big endian) byte order meaning that the most significant
+byte (MSB) is stored at the lowest address.
+
+
+OP_REQ_DEVLIST: Retrieve the list of exported USB devices.
+
+ Offset | Length | Value | Meaning
+-----------+--------+------------+---------------------------------------------------
+ 0 | 2 | 0x0100 | Binary-coded decimal USBIP version number: v1.0.0
+-----------+--------+------------+---------------------------------------------------
+ 2 | 2 | 0x8005 | Command code: Retrieve the list of exported USB
+ | | | devices.
+-----------+--------+------------+---------------------------------------------------
+ 4 | 4 | 0x00000000 | Status: unused, shall be set to 0
+
+OP_REP_DEVLIST: Reply with the list of exported USB devices.
+
+ Offset | Length | Value | Meaning
+-----------+--------+------------+---------------------------------------------------
+ 0 | 2 | 0x0100 | Binary-coded decimal USBIP version number: v1.0.0.
+-----------+--------+------------+---------------------------------------------------
+ 2 | 2 | 0x0005 | Reply code: The list of exported USB devices.
+-----------+--------+------------+---------------------------------------------------
+ 4 | 4 | 0x00000000 | Status: 0 for OK
+-----------+--------+------------+---------------------------------------------------
+ 8 | 4 | n | Number of exported devices: 0 means no exported
+ | | | devices.
+-----------+--------+------------+---------------------------------------------------
+ 0x0C | | | From now on the exported n devices are described,
+ | | | if any. If no devices are exported the message
+ | | | ends with the previous "number of exported
+ | | | devices" field.
+-----------+--------+------------+---------------------------------------------------
+ | 256 | | path: Path of the device on the host exporting the
+ | | | USB device, string closed with zero byte, e.g.
+ | | | "/sys/devices/pci0000:00/0000:00:1d.1/usb3/3-2"
+ | | | The unused bytes shall be filled with zero
+ | | | bytes.
+-----------+--------+------------+---------------------------------------------------
+ 0x10C | 32 | | busid: Bus ID of the exported device, string
+ | | | closed with zero byte, e.g. "3-2". The unused
+ | | | bytes shall be filled with zero bytes.
+-----------+--------+------------+---------------------------------------------------
+ 0x12C | 4 | | busnum
+-----------+--------+------------+---------------------------------------------------
+ 0x130 | 4 | | devnum
+-----------+--------+------------+---------------------------------------------------
+ 0x134 | 4 | | speed
+-----------+--------+------------+---------------------------------------------------
+ 0x138 | 2 | | idVendor
+-----------+--------+------------+---------------------------------------------------
+ 0x13A | 2 | | idProduct
+-----------+--------+------------+---------------------------------------------------
+ 0x13C | 2 | | bcdDevice
+-----------+--------+------------+---------------------------------------------------
+ 0x13E | 1 | | bDeviceClass
+-----------+--------+------------+---------------------------------------------------
+ 0x13F | 1 | | bDeviceSubClass
+-----------+--------+------------+---------------------------------------------------
+ 0x140 | 1 | | bDeviceProtocol
+-----------+--------+------------+---------------------------------------------------
+ 0x141 | 1 | | bConfigurationValue
+-----------+--------+------------+---------------------------------------------------
+ 0x142 | 1 | | bNumConfigurations
+-----------+--------+------------+---------------------------------------------------
+ 0x143 | 1 | | bNumInterfaces
+-----------+--------+------------+---------------------------------------------------
+ 0x144 | | m_0 | From now on each interface is described, all
+ | | | together bNumInterfaces times, with the
+ | | | the following 4 fields:
+-----------+--------+------------+---------------------------------------------------
+ | 1 | | bInterfaceClass
+-----------+--------+------------+---------------------------------------------------
+ 0x145 | 1 | | bInterfaceSubClass
+-----------+--------+------------+---------------------------------------------------
+ 0x146 | 1 | | bInterfaceProtocol
+-----------+--------+------------+---------------------------------------------------
+ 0x147 | 1 | | padding byte for alignment, shall be set to zero
+-----------+--------+------------+---------------------------------------------------
+ 0xC + | | | The second exported USB device starts at i=1
+ i*0x138 + | | | with the busid field.
+ m_(i-1)*4 | | |
+
+OP_REQ_IMPORT: Request to import (attach) a remote USB device.
+
+ Offset | Length | Value | Meaning
+-----------+--------+------------+---------------------------------------------------
+ 0 | 2 | 0x0100 | Binary-coded decimal USBIP version number: v1.0.0
+-----------+--------+------------+---------------------------------------------------
+ 2 | 2 | 0x8003 | Command code: import a remote USB device.
+-----------+--------+------------+---------------------------------------------------
+ 4 | 4 | 0x00000000 | Status: unused, shall be set to 0
+-----------+--------+------------+---------------------------------------------------
+ 8 | 32 | | busid: the busid of the exported device on the
+ | | | remote host. The possible values are taken
+ | | | from the message field OP_REP_DEVLIST.busid.
+ | | | A string closed with zero, the unused bytes
+ | | | shall be filled with zeros.
+-----------+--------+------------+---------------------------------------------------
+
+OP_REP_IMPORT: Reply to import (attach) a remote USB device.
+
+ Offset | Length | Value | Meaning
+-----------+--------+------------+---------------------------------------------------
+ 0 | 2 | 0x0100 | Binary-coded decimal USBIP version number: v1.0.0
+-----------+--------+------------+---------------------------------------------------
+ 2 | 2 | 0x0003 | Reply code: Reply to import.
+-----------+--------+------------+---------------------------------------------------
+ 4 | 4 | 0x00000000 | Status: 0 for OK
+ | | | 1 for error
+-----------+--------+------------+---------------------------------------------------
+ 8 | | | From now on comes the details of the imported
+ | | | device, if the previous status field was OK (0),
+ | | | otherwise the reply ends with the status field.
+-----------+--------+------------+---------------------------------------------------
+ | 256 | | path: Path of the device on the host exporting the
+ | | | USB device, string closed with zero byte, e.g.
+ | | | "/sys/devices/pci0000:00/0000:00:1d.1/usb3/3-2"
+ | | | The unused bytes shall be filled with zero
+ | | | bytes.
+-----------+--------+------------+---------------------------------------------------
+ 0x108 | 32 | | busid: Bus ID of the exported device, string
+ | | | closed with zero byte, e.g. "3-2". The unused
+ | | | bytes shall be filled with zero bytes.
+-----------+--------+------------+---------------------------------------------------
+ 0x128 | 4 | | busnum
+-----------+--------+------------+---------------------------------------------------
+ 0x12C | 4 | | devnum
+-----------+--------+------------+---------------------------------------------------
+ 0x130 | 4 | | speed
+-----------+--------+------------+---------------------------------------------------
+ 0x134 | 2 | | idVendor
+-----------+--------+------------+---------------------------------------------------
+ 0x136 | 2 | | idProduct
+-----------+--------+------------+---------------------------------------------------
+ 0x138 | 2 | | bcdDevice
+-----------+--------+------------+---------------------------------------------------
+ 0x139 | 1 | | bDeviceClass
+-----------+--------+------------+---------------------------------------------------
+ 0x13A | 1 | | bDeviceSubClass
+-----------+--------+------------+---------------------------------------------------
+ 0x13B | 1 | | bDeviceProtocol
+-----------+--------+------------+---------------------------------------------------
+ 0x13C | 1 | | bConfigurationValue
+-----------+--------+------------+---------------------------------------------------
+ 0x13D | 1 | | bNumConfigurations
+-----------+--------+------------+---------------------------------------------------
+ 0x13E | 1 | | bNumInterfaces
+
+USBIP_CMD_SUBMIT: Submit an URB
+
+ Offset | Length | Value | Meaning
+-----------+--------+------------+---------------------------------------------------
+ 0 | 4 | 0x00000001 | command: Submit an URB
+-----------+--------+------------+---------------------------------------------------
+ 4 | 4 | | seqnum: the sequence number of the URB to submit
+-----------+--------+------------+---------------------------------------------------
+ 8 | 4 | | devid
+-----------+--------+------------+---------------------------------------------------
+ 0xC | 4 | | direction: 0: USBIP_DIR_IN
+ | | | 1: USBIP_DIR_OUT
+-----------+--------+------------+---------------------------------------------------
+ 0x10 | 4 | | ep: endpoint number, possible values are: 0...15
+-----------+--------+------------+---------------------------------------------------
+ 0x14 | 4 | | transfer_flags: possible values depend on the
+ | | | URB transfer type, see below
+-----------+--------+------------+---------------------------------------------------
+ 0x18 | 4 | | transfer_buffer_length
+-----------+--------+------------+---------------------------------------------------
+ 0x1C | 4 | | start_frame: specify the selected frame to
+ | | | transmit an ISO frame, ignored if URB_ISO_ASAP
+ | | | is specified at transfer_flags
+-----------+--------+------------+---------------------------------------------------
+ 0x20 | 4 | | number_of_packets: number of ISO packets
+-----------+--------+------------+---------------------------------------------------
+ 0x24 | 4 | | interval: maximum time for the request on the
+ | | | server-side host controller
+-----------+--------+------------+---------------------------------------------------
+ 0x28 | 8 | | setup: data bytes for USB setup, filled with
+ | | | zeros if not used
+-----------+--------+------------+---------------------------------------------------
+ 0x30 | | | URB data. For ISO transfers the padding between
+ | | | each ISO packets is not transmitted.
+
+
+ Allowed transfer_flags | value | control | interrupt | bulk | isochronous
+ -------------------------+------------+---------+-----------+----------+-------------
+ URB_SHORT_NOT_OK | 0x00000001 | only in | only in | only in | no
+ URB_ISO_ASAP | 0x00000002 | no | no | no | yes
+ URB_NO_TRANSFER_DMA_MAP | 0x00000004 | yes | yes | yes | yes
+ URB_NO_FSBR | 0x00000020 | yes | no | no | no
+ URB_ZERO_PACKET | 0x00000040 | no | no | only out | no
+ URB_NO_INTERRUPT | 0x00000080 | yes | yes | yes | yes
+ URB_FREE_BUFFER | 0x00000100 | yes | yes | yes | yes
+ URB_DIR_MASK | 0x00000200 | yes | yes | yes | yes
+
+
+USBIP_RET_SUBMIT: Reply for submitting an URB
+
+ Offset | Length | Value | Meaning
+-----------+--------+------------+---------------------------------------------------
+ 0 | 4 | 0x00000002 | command
+-----------+--------+------------+---------------------------------------------------
+ 4 | 4 | | seqnum: URB sequence number
+-----------+--------+------------+---------------------------------------------------
+ 8 | 4 | | devid
+-----------+--------+------------+---------------------------------------------------
+ 0xC | 4 | | direction: 0: USBIP_DIR_IN
+ | | | 1: USBIP_DIR_OUT
+-----------+--------+------------+---------------------------------------------------
+ 0x10 | 4 | | ep: endpoint number
+-----------+--------+------------+---------------------------------------------------
+ 0x14 | 4 | | status: zero for successful URB transaction,
+ | | | otherwise some kind of error happened.
+-----------+--------+------------+---------------------------------------------------
+ 0x18 | 4 | n | actual_length: number of URB data bytes
+-----------+--------+------------+---------------------------------------------------
+ 0x1C | 4 | | start_frame: for an ISO frame the actually
+ | | | selected frame for transmit.
+-----------+--------+------------+---------------------------------------------------
+ 0x20 | 4 | | number_of_packets
+-----------+--------+------------+---------------------------------------------------
+ 0x24 | 4 | | error_count
+-----------+--------+------------+---------------------------------------------------
+ 0x28 | 8 | | setup: data bytes for USB setup, filled with
+ | | | zeros if not used
+-----------+--------+------------+---------------------------------------------------
+ 0x30 | n | | URB data bytes. For ISO transfers the padding
+ | | | between each ISO packets is not transmitted.
+
+USBIP_CMD_UNLINK: Unlink an URB
+
+ Offset | Length | Value | Meaning
+-----------+--------+------------+---------------------------------------------------
+ 0 | 4 | 0x00000003 | command: URB unlink command
+-----------+--------+------------+---------------------------------------------------
+ 4 | 4 | | seqnum: URB sequence number to unlink: FIXME: is this so?
+-----------+--------+------------+---------------------------------------------------
+ 8 | 4 | | devid
+-----------+--------+------------+---------------------------------------------------
+ 0xC | 4 | | direction: 0: USBIP_DIR_IN
+ | | | 1: USBIP_DIR_OUT
+-----------+--------+------------+---------------------------------------------------
+ 0x10 | 4 | | ep: endpoint number: zero
+-----------+--------+------------+---------------------------------------------------
+ 0x14 | 4 | | seqnum: the URB sequence number given previously
+ | | | at USBIP_CMD_SUBMIT.seqnum field
+
+USBIP_RET_UNLINK: Reply for URB unlink
+
+ Offset | Length | Value | Meaning
+-----------+--------+------------+---------------------------------------------------
+ 0 | 4 | 0x00000004 | command: reply for the URB unlink command
+-----------+--------+------------+---------------------------------------------------
+ 4 | 4 | | seqnum: the unlinked URB sequence number
+-----------+--------+------------+---------------------------------------------------
+ 8 | 4 | | devid
+-----------+--------+------------+---------------------------------------------------
+ 0xC | 4 | | direction: 0: USBIP_DIR_IN
+ | | | 1: USBIP_DIR_OUT
+-----------+--------+------------+---------------------------------------------------
+ 0x10 | 4 | | ep: endpoint number
+-----------+--------+------------+---------------------------------------------------
+ 0x14 | 4 | | status: This is the value contained in the
+ | | | urb->status in the URB completition handler.
+ | | | FIXME: a better explanation needed.