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+===============
+USB/IP protocol
+===============
+
+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 transfer 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 | Description |
++===========+========+============+===================================================+
+| 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 | Description |
++===========+========+============+===================================================+
+| 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 | Description |
++===========+========+============+===================================================+
+| 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 | Description |
++===========+========+============+===================================================+
+| 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 | Description |
++===========+========+============+===================================================+
+| 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_OUT |
+| | | | - 1: USBIP_DIR_IN |
++-----------+--------+------------+---------------------------------------------------+
+| 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_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 | Description |
++===========+========+============+===================================================+
+| 0 | 4 | 0x00000003 | command |
++-----------+--------+------------+---------------------------------------------------+
+| 4 | 4 | | seqnum: URB sequence number |
++-----------+--------+------------+---------------------------------------------------+
+| 8 | 4 | | devid |
++-----------+--------+------------+---------------------------------------------------+
+| 0xC | 4 | | direction: |
+| | | | |
+| | | | - 0: USBIP_DIR_OUT |
+| | | | - 1: USBIP_DIR_IN |
++-----------+--------+------------+---------------------------------------------------+
+| 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 | Description |
++===========+========+============+===================================================+
+| 0 | 4 | 0x00000002 | 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_OUT |
+| | | | - 1: USBIP_DIR_IN |
++-----------+--------+------------+---------------------------------------------------+
+| 0x10 | 4 | | ep: endpoint number: zero |
++-----------+--------+------------+---------------------------------------------------+
+| 0x14 | 4 | | seqnum: the URB sequence number given previously |
+| | | | at USBIP_CMD_SUBMIT.seqnum field |
++-----------+--------+------------+---------------------------------------------------+
+| 0x30 | n | | URB data bytes. For ISO transfers the padding |
+| | | | between each ISO packets is not transmitted. |
++-----------+--------+------------+---------------------------------------------------+
+
+USBIP_RET_UNLINK:
+ Reply for URB unlink
+
++-----------+--------+------------+---------------------------------------------------+
+| Offset | Length | Value | Description |
++===========+========+============+===================================================+
+| 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_OUT |
+| | | | - 1: USBIP_DIR_IN |
++-----------+--------+------------+---------------------------------------------------+
+| 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. |
++-----------+--------+------------+---------------------------------------------------+
+| 0x30 | n | | URB data bytes. For ISO transfers the padding |
+| | | | between each ISO packets is not transmitted. |
++-----------+--------+------------+---------------------------------------------------+