linux/Documentation/usb/usbip_protocol.rst
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   1===============
   2USB/IP protocol
   3===============
   4
   5Architecture
   6============
   7
   8The USB/IP protocol follows a server/client architecture. The server exports the
   9USB devices and the clients import them. The device driver for the exported
  10USB device runs on the client machine.
  11
  12The client may ask for the list of the exported USB devices. To get the list the
  13client opens a TCP/IP connection to the server, and sends an OP_REQ_DEVLIST
  14packet on top of the TCP/IP connection (so the actual OP_REQ_DEVLIST may be sent
  15in one or more pieces at the low level transport layer). The server sends back
  16the OP_REP_DEVLIST packet which lists the exported USB devices. Finally the
  17TCP/IP connection is closed.
  18
  19::
  20
  21 virtual host controller                                 usb host
  22      "client"                                           "server"
  23  (imports USB devices)                             (exports USB devices)
  24          |                                                 |
  25          |                  OP_REQ_DEVLIST                 |
  26          | ----------------------------------------------> |
  27          |                                                 |
  28          |                  OP_REP_DEVLIST                 |
  29          | <---------------------------------------------- |
  30          |                                                 |
  31
  32Once the client knows the list of exported USB devices it may decide to use one
  33of them. First the client opens a TCP/IP connection to the server and
  34sends an OP_REQ_IMPORT packet. The server replies with OP_REP_IMPORT. If the
  35import was successful the TCP/IP connection remains open and will be used
  36to transfer the URB traffic between the client and the server. The client may
  37send two types of packets: the USBIP_CMD_SUBMIT to submit an URB, and
  38USBIP_CMD_UNLINK to unlink a previously submitted URB. The answers of the
  39server may be USBIP_RET_SUBMIT and USBIP_RET_UNLINK respectively.
  40
  41::
  42
  43 virtual host controller                                 usb host
  44      "client"                                           "server"
  45  (imports USB devices)                             (exports USB devices)
  46          |                                                 |
  47          |                  OP_REQ_IMPORT                  |
  48          | ----------------------------------------------> |
  49          |                                                 |
  50          |                  OP_REP_IMPORT                  |
  51          | <---------------------------------------------- |
  52          |                                                 |
  53          |                                                 |
  54          |            USBIP_CMD_SUBMIT(seqnum = n)         |
  55          | ----------------------------------------------> |
  56          |                                                 |
  57          |            USBIP_RET_SUBMIT(seqnum = n)         |
  58          | <---------------------------------------------- |
  59          |                        .                        |
  60          |                        :                        |
  61          |                                                 |
  62          |            USBIP_CMD_SUBMIT(seqnum = m)         |
  63          | ----------------------------------------------> |
  64          |                                                 |
  65          |            USBIP_CMD_SUBMIT(seqnum = m+1)       |
  66          | ----------------------------------------------> |
  67          |                                                 |
  68          |            USBIP_CMD_SUBMIT(seqnum = m+2)       |
  69          | ----------------------------------------------> |
  70          |                                                 |
  71          |            USBIP_RET_SUBMIT(seqnum = m)         |
  72          | <---------------------------------------------- |
  73          |                                                 |
  74          |            USBIP_CMD_SUBMIT(seqnum = m+3)       |
  75          | ----------------------------------------------> |
  76          |                                                 |
  77          |            USBIP_RET_SUBMIT(seqnum = m+1)       |
  78          | <---------------------------------------------- |
  79          |                                                 |
  80          |            USBIP_CMD_SUBMIT(seqnum = m+4)       |
  81          | ----------------------------------------------> |
  82          |                                                 |
  83          |            USBIP_RET_SUBMIT(seqnum = m+2)       |
  84          | <---------------------------------------------- |
  85          |                        .                        |
  86          |                        :                        |
  87
  88For UNLINK, note that after a successful USBIP_RET_UNLINK, the unlinked URB
  89submission would not have a corresponding USBIP_RET_SUBMIT (this is explained in
  90function stub_recv_cmd_unlink of drivers/usb/usbip/stub_rx.c).
  91
  92::
  93
  94 virtual host controller                                 usb host
  95      "client"                                           "server"
  96  (imports USB devices)                             (exports USB devices)
  97          |                                                 |
  98          |            USBIP_CMD_SUBMIT(seqnum = p)         |
  99          | ----------------------------------------------> |
 100          |                                                 |
 101          |               USBIP_CMD_UNLINK                  |
 102          |         (seqnum = p+1, unlink_seqnum = p)       |
 103          | ----------------------------------------------> |
 104          |                                                 |
 105          |               USBIP_RET_UNLINK                  |
 106          |        (seqnum = p+1, status = -ECONNRESET)     |
 107          | <---------------------------------------------- |
 108          |                                                 |
 109          |         Note: No USBIP_RET_SUBMIT(seqnum = p)   |
 110          | <--X---X---X---X---X---X---X---X---X---X---X--- |
 111          |                        .                        |
 112          |                        :                        |
 113          |                                                 |
 114          |            USBIP_CMD_SUBMIT(seqnum = q)         |
 115          | ----------------------------------------------> |
 116          |                                                 |
 117          |            USBIP_RET_SUBMIT(seqnum = q)         |
 118          | <---------------------------------------------- |
 119          |                                                 |
 120          |               USBIP_CMD_UNLINK                  |
 121          |         (seqnum = q+1, unlink_seqnum = q)       |
 122          | ----------------------------------------------> |
 123          |                                                 |
 124          |               USBIP_RET_UNLINK                  |
 125          |           (seqnum = q+1, status = 0)            |
 126          | <---------------------------------------------- |
 127          |                                                 |
 128
 129The fields are in network (big endian) byte order meaning that the most significant
 130byte (MSB) is stored at the lowest address.
 131
 132Protocol Version
 133================
 134
 135The documented USBIP version is v1.1.1. The binary representation of this
 136version in message headers is 0x0111.
 137
 138This is defined in tools/usb/usbip/configure.ac
 139
 140Message Format
 141==============
 142
 143OP_REQ_DEVLIST:
 144        Retrieve the list of exported USB devices.
 145
 146+-----------+--------+------------+---------------------------------------------------+
 147| Offset    | Length | Value      | Description                                       |
 148+===========+========+============+===================================================+
 149| 0         | 2      |            | USBIP version                                     |
 150+-----------+--------+------------+---------------------------------------------------+
 151| 2         | 2      | 0x8005     | Command code: Retrieve the list of exported USB   |
 152|           |        |            | devices.                                          |
 153+-----------+--------+------------+---------------------------------------------------+
 154| 4         | 4      | 0x00000000 | Status: unused, shall be set to 0                 |
 155+-----------+--------+------------+---------------------------------------------------+
 156
 157OP_REP_DEVLIST:
 158        Reply with the list of exported USB devices.
 159
 160+-----------+--------+------------+---------------------------------------------------+
 161| Offset    | Length | Value      | Description                                       |
 162+===========+========+============+===================================================+
 163| 0         | 2      |            | USBIP version                                     |
 164+-----------+--------+------------+---------------------------------------------------+
 165| 2         | 2      | 0x0005     | Reply code: The list of exported USB devices.     |
 166+-----------+--------+------------+---------------------------------------------------+
 167| 4         | 4      | 0x00000000 | Status: 0 for OK                                  |
 168+-----------+--------+------------+---------------------------------------------------+
 169| 8         | 4      | n          | Number of exported devices: 0 means no exported   |
 170|           |        |            | devices.                                          |
 171+-----------+--------+------------+---------------------------------------------------+
 172| 0x0C      |        |            | From now on the exported n devices are described, |
 173|           |        |            | if any. If no devices are exported the message    |
 174|           |        |            | ends with the previous "number of exported        |
 175|           |        |            | devices" field.                                   |
 176+-----------+--------+------------+---------------------------------------------------+
 177|           | 256    |            | path: Path of the device on the host exporting the|
 178|           |        |            | USB device, string closed with zero byte, e.g.    |
 179|           |        |            | "/sys/devices/pci0000:00/0000:00:1d.1/usb3/3-2"   |
 180|           |        |            | The unused bytes shall be filled with zero        |
 181|           |        |            | bytes.                                            |
 182+-----------+--------+------------+---------------------------------------------------+
 183| 0x10C     | 32     |            | busid: Bus ID of the exported device, string      |
 184|           |        |            | closed with zero byte, e.g. "3-2". The unused     |
 185|           |        |            | bytes shall be filled with zero bytes.            |
 186+-----------+--------+------------+---------------------------------------------------+
 187| 0x12C     | 4      |            | busnum                                            |
 188+-----------+--------+------------+---------------------------------------------------+
 189| 0x130     | 4      |            | devnum                                            |
 190+-----------+--------+------------+---------------------------------------------------+
 191| 0x134     | 4      |            | speed                                             |
 192+-----------+--------+------------+---------------------------------------------------+
 193| 0x138     | 2      |            | idVendor                                          |
 194+-----------+--------+------------+---------------------------------------------------+
 195| 0x13A     | 2      |            | idProduct                                         |
 196+-----------+--------+------------+---------------------------------------------------+
 197| 0x13C     | 2      |            | bcdDevice                                         |
 198+-----------+--------+------------+---------------------------------------------------+
 199| 0x13E     | 1      |            | bDeviceClass                                      |
 200+-----------+--------+------------+---------------------------------------------------+
 201| 0x13F     | 1      |            | bDeviceSubClass                                   |
 202+-----------+--------+------------+---------------------------------------------------+
 203| 0x140     | 1      |            | bDeviceProtocol                                   |
 204+-----------+--------+------------+---------------------------------------------------+
 205| 0x141     | 1      |            | bConfigurationValue                               |
 206+-----------+--------+------------+---------------------------------------------------+
 207| 0x142     | 1      |            | bNumConfigurations                                |
 208+-----------+--------+------------+---------------------------------------------------+
 209| 0x143     | 1      |            | bNumInterfaces                                    |
 210+-----------+--------+------------+---------------------------------------------------+
 211| 0x144     |        | m_0        | From now on each interface is described, all      |
 212|           |        |            | together bNumInterfaces times, with the following |
 213|           |        |            | 4 fields:                                         |
 214+-----------+--------+------------+---------------------------------------------------+
 215|           | 1      |            | bInterfaceClass                                   |
 216+-----------+--------+------------+---------------------------------------------------+
 217| 0x145     | 1      |            | bInterfaceSubClass                                |
 218+-----------+--------+------------+---------------------------------------------------+
 219| 0x146     | 1      |            | bInterfaceProtocol                                |
 220+-----------+--------+------------+---------------------------------------------------+
 221| 0x147     | 1      |            | padding byte for alignment, shall be set to zero  |
 222+-----------+--------+------------+---------------------------------------------------+
 223| 0xC +     |        |            | The second exported USB device starts at i=1      |
 224| i*0x138 + |        |            | with the path field.                              |
 225| m_(i-1)*4 |        |            |                                                   |
 226+-----------+--------+------------+---------------------------------------------------+
 227
 228OP_REQ_IMPORT:
 229        Request to import (attach) a remote USB device.
 230
 231+-----------+--------+------------+---------------------------------------------------+
 232| Offset    | Length | Value      | Description                                       |
 233+===========+========+============+===================================================+
 234| 0         | 2      |            | USBIP version                                     |
 235+-----------+--------+------------+---------------------------------------------------+
 236| 2         | 2      | 0x8003     | Command code: import a remote USB device.         |
 237+-----------+--------+------------+---------------------------------------------------+
 238| 4         | 4      | 0x00000000 | Status: unused, shall be set to 0                 |
 239+-----------+--------+------------+---------------------------------------------------+
 240| 8         | 32     |            | busid: the busid of the exported device on the    |
 241|           |        |            | remote host. The possible values are taken        |
 242|           |        |            | from the message field OP_REP_DEVLIST.busid.      |
 243|           |        |            | A string closed with zero, the unused bytes       |
 244|           |        |            | shall be filled with zeros.                       |
 245+-----------+--------+------------+---------------------------------------------------+
 246
 247OP_REP_IMPORT:
 248        Reply to import (attach) a remote USB device.
 249
 250+-----------+--------+------------+---------------------------------------------------+
 251| Offset    | Length | Value      | Description                                       |
 252+===========+========+============+===================================================+
 253| 0         | 2      |            | USBIP version                                     |
 254+-----------+--------+------------+---------------------------------------------------+
 255| 2         | 2      | 0x0003     | Reply code: Reply to import.                      |
 256+-----------+--------+------------+---------------------------------------------------+
 257| 4         | 4      | 0x00000000 | Status:                                           |
 258|           |        |            |                                                   |
 259|           |        |            |   - 0 for OK                                      |
 260|           |        |            |   - 1 for error                                   |
 261+-----------+--------+------------+---------------------------------------------------+
 262| 8         |        |            | From now on comes the details of the imported     |
 263|           |        |            | device, if the previous status field was OK (0),  |
 264|           |        |            | otherwise the reply ends with the status field.   |
 265+-----------+--------+------------+---------------------------------------------------+
 266|           | 256    |            | path: Path of the device on the host exporting the|
 267|           |        |            | USB device, string closed with zero byte, e.g.    |
 268|           |        |            | "/sys/devices/pci0000:00/0000:00:1d.1/usb3/3-2"   |
 269|           |        |            | The unused bytes shall be filled with zero        |
 270|           |        |            | bytes.                                            |
 271+-----------+--------+------------+---------------------------------------------------+
 272| 0x108     | 32     |            | busid: Bus ID of the exported device, string      |
 273|           |        |            | closed with zero byte, e.g. "3-2". The unused     |
 274|           |        |            | bytes shall be filled with zero bytes.            |
 275+-----------+--------+------------+---------------------------------------------------+
 276| 0x128     | 4      |            | busnum                                            |
 277+-----------+--------+------------+---------------------------------------------------+
 278| 0x12C     | 4      |            | devnum                                            |
 279+-----------+--------+------------+---------------------------------------------------+
 280| 0x130     | 4      |            | speed                                             |
 281+-----------+--------+------------+---------------------------------------------------+
 282| 0x134     | 2      |            | idVendor                                          |
 283+-----------+--------+------------+---------------------------------------------------+
 284| 0x136     | 2      |            | idProduct                                         |
 285+-----------+--------+------------+---------------------------------------------------+
 286| 0x138     | 2      |            | bcdDevice                                         |
 287+-----------+--------+------------+---------------------------------------------------+
 288| 0x139     | 1      |            | bDeviceClass                                      |
 289+-----------+--------+------------+---------------------------------------------------+
 290| 0x13A     | 1      |            | bDeviceSubClass                                   |
 291+-----------+--------+------------+---------------------------------------------------+
 292| 0x13B     | 1      |            | bDeviceProtocol                                   |
 293+-----------+--------+------------+---------------------------------------------------+
 294| 0x13C     | 1      |            | bConfigurationValue                               |
 295+-----------+--------+------------+---------------------------------------------------+
 296| 0x13D     | 1      |            | bNumConfigurations                                |
 297+-----------+--------+------------+---------------------------------------------------+
 298| 0x13E     | 1      |            | bNumInterfaces                                    |
 299+-----------+--------+------------+---------------------------------------------------+
 300
 301The following four commands have a common basic header called
 302'usbip_header_basic', and their headers, called 'usbip_header' (before
 303transfer_buffer payload), have the same length, therefore paddings are needed.
 304
 305usbip_header_basic:
 306
 307+-----------+--------+---------------------------------------------------+
 308| Offset    | Length | Description                                       |
 309+===========+========+===================================================+
 310| 0         | 4      | command                                           |
 311+-----------+--------+---------------------------------------------------+
 312| 4         | 4      | seqnum: sequential number that identifies requests|
 313|           |        | and corresponding responses;                      |
 314|           |        | incremented per connection                        |
 315+-----------+--------+---------------------------------------------------+
 316| 8         | 4      | devid: specifies a remote USB device uniquely     |
 317|           |        | instead of busnum and devnum;                     |
 318|           |        | for client (request), this value is               |
 319|           |        | ((busnum << 16) | devnum);                        |
 320|           |        | for server (response), this shall be set to 0     |
 321+-----------+--------+---------------------------------------------------+
 322| 0xC       | 4      | direction:                                        |
 323|           |        |                                                   |
 324|           |        |    - 0: USBIP_DIR_OUT                             |
 325|           |        |    - 1: USBIP_DIR_IN                              |
 326|           |        |                                                   |
 327|           |        | only used by client, for server this shall be 0   |
 328+-----------+--------+---------------------------------------------------+
 329| 0x10      | 4      | ep: endpoint number                               |
 330|           |        | only used by client, for server this shall be 0;  |
 331|           |        | for UNLINK, this shall be 0                       |
 332+-----------+--------+---------------------------------------------------+
 333
 334USBIP_CMD_SUBMIT:
 335        Submit an URB
 336
 337+-----------+--------+---------------------------------------------------+
 338| Offset    | Length | Description                                       |
 339+===========+========+===================================================+
 340| 0         | 20     | usbip_header_basic, 'command' shall be 0x00000001 |
 341+-----------+--------+---------------------------------------------------+
 342| 0x14      | 4      | transfer_flags: possible values depend on the     |
 343|           |        | URB transfer_flags (refer to URB doc in           |
 344|           |        | Documentation/driver-api/usb/URB.rst)             |
 345|           |        | but with URB_NO_TRANSFER_DMA_MAP masked. Refer to |
 346|           |        | function usbip_pack_cmd_submit and function       |
 347|           |        | tweak_transfer_flags in drivers/usb/usbip/        |
 348|           |        | usbip_common.c. The following fields may also ref |
 349|           |        | to function usbip_pack_cmd_submit and URB doc     |
 350+-----------+--------+---------------------------------------------------+
 351| 0x18      | 4      | transfer_buffer_length:                           |
 352|           |        | use URB transfer_buffer_length                    |
 353+-----------+--------+---------------------------------------------------+
 354| 0x1C      | 4      | start_frame: use URB start_frame;                 |
 355|           |        | initial frame for ISO transfer;                   |
 356|           |        | shall be set to 0 if not ISO transfer             |
 357+-----------+--------+---------------------------------------------------+
 358| 0x20      | 4      | number_of_packets: number of ISO packets;         |
 359|           |        | shall be set to 0xffffffff if not ISO transfer    |
 360+-----------+--------+---------------------------------------------------+
 361| 0x24      | 4      | interval: maximum time for the request on the     |
 362|           |        | server-side host controller                       |
 363+-----------+--------+---------------------------------------------------+
 364| 0x28      | 8      | setup: data bytes for USB setup, filled with      |
 365|           |        | zeros if not used.                                |
 366+-----------+--------+---------------------------------------------------+
 367| 0x30      | n      | transfer_buffer.                                  |
 368|           |        | If direction is USBIP_DIR_OUT then n equals       |
 369|           |        | transfer_buffer_length; otherwise n equals 0.     |
 370|           |        | For ISO transfers the padding between each ISO    |
 371|           |        | packets is not transmitted.                       |
 372+-----------+--------+---------------------------------------------------+
 373| 0x30+n    | m      | iso_packet_descriptor                             |
 374+-----------+--------+---------------------------------------------------+
 375
 376USBIP_RET_SUBMIT:
 377        Reply for submitting an URB
 378
 379+-----------+--------+---------------------------------------------------+
 380| Offset    | Length | Description                                       |
 381+===========+========+===================================================+
 382| 0         | 20     | usbip_header_basic, 'command' shall be 0x00000003 |
 383+-----------+--------+---------------------------------------------------+
 384| 0x14      | 4      | status: zero for successful URB transaction,      |
 385|           |        | otherwise some kind of error happened.            |
 386+-----------+--------+---------------------------------------------------+
 387| 0x18      | 4      | actual_length: number of URB data bytes;          |
 388|           |        | use URB actual_length                             |
 389+-----------+--------+---------------------------------------------------+
 390| 0x1C      | 4      | start_frame: use URB start_frame;                 |
 391|           |        | initial frame for ISO transfer;                   |
 392|           |        | shall be set to 0 if not ISO transfer             |
 393+-----------+--------+---------------------------------------------------+
 394| 0x20      | 4      | number_of_packets: number of ISO packets;         |
 395|           |        | shall be set to 0xffffffff if not ISO transfer    |
 396+-----------+--------+---------------------------------------------------+
 397| 0x24      | 4      | error_count                                       |
 398+-----------+--------+---------------------------------------------------+
 399| 0x28      | 8      | padding, shall be set to 0                        |
 400+-----------+--------+---------------------------------------------------+
 401| 0x30      | n      | transfer_buffer.                                  |
 402|           |        | If direction is USBIP_DIR_IN then n equals        |
 403|           |        | actual_length; otherwise n equals 0.              |
 404|           |        | For ISO transfers the padding between each ISO    |
 405|           |        | packets is not transmitted.                       |
 406+-----------+--------+---------------------------------------------------+
 407| 0x30+n    | m      | iso_packet_descriptor                             |
 408+-----------+--------+---------------------------------------------------+
 409
 410USBIP_CMD_UNLINK:
 411        Unlink an URB
 412
 413+-----------+--------+---------------------------------------------------+
 414| Offset    | Length | Description                                       |
 415+===========+========+===================================================+
 416| 0         | 20     | usbip_header_basic, 'command' shall be 0x00000002 |
 417+-----------+--------+---------------------------------------------------+
 418| 0x14      | 4      | unlink_seqnum, of the SUBMIT request to unlink    |
 419+-----------+--------+---------------------------------------------------+
 420| 0x18      | 24     | padding, shall be set to 0                        |
 421+-----------+--------+---------------------------------------------------+
 422
 423USBIP_RET_UNLINK:
 424        Reply for URB unlink
 425
 426+-----------+--------+---------------------------------------------------+
 427| Offset    | Length | Description                                       |
 428+===========+========+===================================================+
 429| 0         | 20     | usbip_header_basic, 'command' shall be 0x00000004 |
 430+-----------+--------+---------------------------------------------------+
 431| 0x14      | 4      | status: This is similar to the status of          |
 432|           |        | USBIP_RET_SUBMIT (share the same memory offset).  |
 433|           |        | When UNLINK is successful, status is -ECONNRESET; |
 434|           |        | when USBIP_CMD_UNLINK is after USBIP_RET_SUBMIT   |
 435|           |        | status is 0                                       |
 436+-----------+--------+---------------------------------------------------+
 437| 0x18      | 24     | padding, shall be set to 0                        |
 438+-----------+--------+---------------------------------------------------+
 439
 440EXAMPLE
 441=======
 442
 443  The following data is captured from wire with Human Interface Devices (HID)
 444  payload
 445
 446::
 447
 448  CmdIntrIN:  00000001 00000d05 0001000f 00000001 00000001 00000200 00000040 ffffffff 00000000 00000004 00000000 00000000
 449  CmdIntrOUT: 00000001 00000d06 0001000f 00000000 00000001 00000000 00000040 ffffffff 00000000 00000004 00000000 00000000
 450              ffffffff860008a784ce5ae212376300000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
 451  RetIntrOut: 00000003 00000d06 00000000 00000000 00000000 00000000 00000040 ffffffff 00000000 00000000 00000000 00000000
 452  RetIntrIn:  00000003 00000d05 00000000 00000000 00000000 00000000 00000040 ffffffff 00000000 00000000 00000000 00000000
 453              ffffffff860011a784ce5ae2123763612891b1020100000400000000000000000000000000000000000000000000000000000000000000000000000000000000
 454