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17af793217
The old document for usbip protocol is misleading and hard to read:
* Some fields in header are incorrect
* Explanation of some fields are unclear or even wrong
* Padding of header (namely all headers have the same length) is
not explicitly pointed out, which is crucial for stream protocol
like TCP
Major changes:
* Document the correct field as described in the codebase.
* Document the padding in usbip headers. This is crucial for TCP
stream hence these padding should be explicitly point out.
In code these padding are implemented by a union of all headers.
* Fix two FIXME related to usbip unlink and Document the behavior
of unlink in different situation.
* Clarify some field with more accurate explanation, like those
fields associated with URB. Some constraints are extracted from
code.
* Delete specific transfer_flag doc in usbip as it should be
documented by the URB doc in Documentation/driver-api/usb/URB.rst
* Add data captured from wire as example
Version change:
From "PRELIMINARY DRAFT, MAY CONTAIN MISTAKES, 28 Jun 2011"
To "Version 1, 31 Mar 2021"
Co-developed-by: Alexandre Demers <alexandre.f.demers@gmail.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Hongren Zheng <i@zenithal.me>
Link: https://lore.kernel.org/r/YGNZHfmAbHO6fyAr@Sun
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
454 lines
29 KiB
ReStructuredText
454 lines
29 KiB
ReStructuredText
===============
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USB/IP protocol
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===============
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Architecture
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============
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The USB/IP protocol follows a server/client architecture. The server exports the
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USB devices and the clients import them. The device driver for the exported
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USB device runs on the client machine.
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The client may ask for the list of the exported USB devices. To get the list the
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client opens a TCP/IP connection to the server, and sends an OP_REQ_DEVLIST
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packet on top of the TCP/IP connection (so the actual OP_REQ_DEVLIST may be sent
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in one or more pieces at the low level transport layer). The server sends back
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the OP_REP_DEVLIST packet which lists the exported USB devices. Finally the
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TCP/IP connection is closed.
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::
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virtual host controller usb host
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"client" "server"
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(imports USB devices) (exports USB devices)
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| |
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| OP_REQ_DEVLIST |
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| ----------------------------------------------> |
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| OP_REP_DEVLIST |
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| <---------------------------------------------- |
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| |
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Once the client knows the list of exported USB devices it may decide to use one
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of them. First the client opens a TCP/IP connection to the server and
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sends an OP_REQ_IMPORT packet. The server replies with OP_REP_IMPORT. If the
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import was successful the TCP/IP connection remains open and will be used
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to transfer the URB traffic between the client and the server. The client may
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send two types of packets: the USBIP_CMD_SUBMIT to submit an URB, and
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USBIP_CMD_UNLINK to unlink a previously submitted URB. The answers of the
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server may be USBIP_RET_SUBMIT and USBIP_RET_UNLINK respectively.
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::
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virtual host controller usb host
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"client" "server"
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(imports USB devices) (exports USB devices)
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| |
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| OP_REQ_IMPORT |
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| ----------------------------------------------> |
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| OP_REP_IMPORT |
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| <---------------------------------------------- |
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| USBIP_CMD_SUBMIT(seqnum = n) |
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| ----------------------------------------------> |
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| USBIP_RET_SUBMIT(seqnum = n) |
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| <---------------------------------------------- |
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| . |
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| : |
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| USBIP_CMD_SUBMIT(seqnum = m) |
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| ----------------------------------------------> |
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| USBIP_CMD_SUBMIT(seqnum = m+1) |
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| ----------------------------------------------> |
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| USBIP_CMD_SUBMIT(seqnum = m+2) |
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| ----------------------------------------------> |
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| USBIP_RET_SUBMIT(seqnum = m) |
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| <---------------------------------------------- |
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| USBIP_CMD_SUBMIT(seqnum = m+3) |
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| ----------------------------------------------> |
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| USBIP_RET_SUBMIT(seqnum = m+1) |
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| <---------------------------------------------- |
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| USBIP_CMD_SUBMIT(seqnum = m+4) |
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| ----------------------------------------------> |
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| USBIP_RET_SUBMIT(seqnum = m+2) |
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| <---------------------------------------------- |
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| . |
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| : |
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For UNLINK, note that after a successful USBIP_RET_UNLINK, the unlinked URB
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submission would not have a corresponding USBIP_RET_SUBMIT (this is explained in
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function stub_recv_cmd_unlink of drivers/usb/usbip/stub_rx.c).
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::
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virtual host controller usb host
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"client" "server"
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(imports USB devices) (exports USB devices)
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| |
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| USBIP_CMD_SUBMIT(seqnum = p) |
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| ----------------------------------------------> |
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| USBIP_CMD_UNLINK |
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| (seqnum = p+1, unlink_seqnum = p) |
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| ----------------------------------------------> |
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| USBIP_RET_UNLINK |
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| (seqnum = p+1, status = -ECONNRESET) |
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| <---------------------------------------------- |
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| |
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| Note: No USBIP_RET_SUBMIT(seqnum = p) |
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| <--X---X---X---X---X---X---X---X---X---X---X--- |
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| . |
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| : |
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| USBIP_CMD_SUBMIT(seqnum = q) |
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| ----------------------------------------------> |
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| USBIP_RET_SUBMIT(seqnum = q) |
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| <---------------------------------------------- |
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| USBIP_CMD_UNLINK |
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| (seqnum = q+1, unlink_seqnum = q) |
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| ----------------------------------------------> |
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| USBIP_RET_UNLINK |
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| (seqnum = q+1, status = 0) |
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| <---------------------------------------------- |
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The fields are in network (big endian) byte order meaning that the most significant
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byte (MSB) is stored at the lowest address.
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Protocol Version
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================
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The documented USBIP version is v1.1.1. The binary representation of this
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version in message headers is 0x0111.
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This is defined in tools/usb/usbip/configure.ac
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Message Format
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==============
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OP_REQ_DEVLIST:
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Retrieve the list of exported USB devices.
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+-----------+--------+------------+---------------------------------------------------+
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| Offset | Length | Value | Description |
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+===========+========+============+===================================================+
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| 0 | 2 | | USBIP version |
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+-----------+--------+------------+---------------------------------------------------+
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| 2 | 2 | 0x8005 | Command code: Retrieve the list of exported USB |
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| | | | devices. |
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+-----------+--------+------------+---------------------------------------------------+
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| 4 | 4 | 0x00000000 | Status: unused, shall be set to 0 |
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+-----------+--------+------------+---------------------------------------------------+
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OP_REP_DEVLIST:
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Reply with the list of exported USB devices.
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+-----------+--------+------------+---------------------------------------------------+
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| Offset | Length | Value | Description |
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+===========+========+============+===================================================+
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| 0 | 2 | | USBIP version |
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+-----------+--------+------------+---------------------------------------------------+
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| 2 | 2 | 0x0005 | Reply code: The list of exported USB devices. |
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+-----------+--------+------------+---------------------------------------------------+
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| 4 | 4 | 0x00000000 | Status: 0 for OK |
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+-----------+--------+------------+---------------------------------------------------+
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| 8 | 4 | n | Number of exported devices: 0 means no exported |
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| | | | devices. |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x0C | | | From now on the exported n devices are described, |
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| | | | if any. If no devices are exported the message |
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| | | | ends with the previous "number of exported |
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| | | | devices" field. |
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+-----------+--------+------------+---------------------------------------------------+
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| | 256 | | path: Path of the device on the host exporting the|
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| | | | USB device, string closed with zero byte, e.g. |
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| | | | "/sys/devices/pci0000:00/0000:00:1d.1/usb3/3-2" |
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| | | | The unused bytes shall be filled with zero |
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| | | | bytes. |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x10C | 32 | | busid: Bus ID of the exported device, string |
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| | | | closed with zero byte, e.g. "3-2". The unused |
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| | | | bytes shall be filled with zero bytes. |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x12C | 4 | | busnum |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x130 | 4 | | devnum |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x134 | 4 | | speed |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x138 | 2 | | idVendor |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x13A | 2 | | idProduct |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x13C | 2 | | bcdDevice |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x13E | 1 | | bDeviceClass |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x13F | 1 | | bDeviceSubClass |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x140 | 1 | | bDeviceProtocol |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x141 | 1 | | bConfigurationValue |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x142 | 1 | | bNumConfigurations |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x143 | 1 | | bNumInterfaces |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x144 | | m_0 | From now on each interface is described, all |
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| | | | together bNumInterfaces times, with the following |
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| | | | 4 fields: |
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+-----------+--------+------------+---------------------------------------------------+
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| | 1 | | bInterfaceClass |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x145 | 1 | | bInterfaceSubClass |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x146 | 1 | | bInterfaceProtocol |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x147 | 1 | | padding byte for alignment, shall be set to zero |
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+-----------+--------+------------+---------------------------------------------------+
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| 0xC + | | | The second exported USB device starts at i=1 |
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| i*0x138 + | | | with the path field. |
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| m_(i-1)*4 | | | |
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+-----------+--------+------------+---------------------------------------------------+
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OP_REQ_IMPORT:
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Request to import (attach) a remote USB device.
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+-----------+--------+------------+---------------------------------------------------+
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| Offset | Length | Value | Description |
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+===========+========+============+===================================================+
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| 0 | 2 | | USBIP version |
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+-----------+--------+------------+---------------------------------------------------+
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| 2 | 2 | 0x8003 | Command code: import a remote USB device. |
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+-----------+--------+------------+---------------------------------------------------+
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| 4 | 4 | 0x00000000 | Status: unused, shall be set to 0 |
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+-----------+--------+------------+---------------------------------------------------+
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| 8 | 32 | | busid: the busid of the exported device on the |
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| | | | remote host. The possible values are taken |
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| | | | from the message field OP_REP_DEVLIST.busid. |
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| | | | A string closed with zero, the unused bytes |
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| | | | shall be filled with zeros. |
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+-----------+--------+------------+---------------------------------------------------+
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OP_REP_IMPORT:
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Reply to import (attach) a remote USB device.
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+-----------+--------+------------+---------------------------------------------------+
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| Offset | Length | Value | Description |
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+===========+========+============+===================================================+
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| 0 | 2 | | USBIP version |
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+-----------+--------+------------+---------------------------------------------------+
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| 2 | 2 | 0x0003 | Reply code: Reply to import. |
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+-----------+--------+------------+---------------------------------------------------+
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| 4 | 4 | 0x00000000 | Status: |
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| | | | |
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| | | | - 0 for OK |
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| | | | - 1 for error |
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+-----------+--------+------------+---------------------------------------------------+
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| 8 | | | From now on comes the details of the imported |
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| | | | device, if the previous status field was OK (0), |
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| | | | otherwise the reply ends with the status field. |
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+-----------+--------+------------+---------------------------------------------------+
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| | 256 | | path: Path of the device on the host exporting the|
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| | | | USB device, string closed with zero byte, e.g. |
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| | | | "/sys/devices/pci0000:00/0000:00:1d.1/usb3/3-2" |
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| | | | The unused bytes shall be filled with zero |
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| | | | bytes. |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x108 | 32 | | busid: Bus ID of the exported device, string |
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| | | | closed with zero byte, e.g. "3-2". The unused |
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| | | | bytes shall be filled with zero bytes. |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x128 | 4 | | busnum |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x12C | 4 | | devnum |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x130 | 4 | | speed |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x134 | 2 | | idVendor |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x136 | 2 | | idProduct |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x138 | 2 | | bcdDevice |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x139 | 1 | | bDeviceClass |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x13A | 1 | | bDeviceSubClass |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x13B | 1 | | bDeviceProtocol |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x13C | 1 | | bConfigurationValue |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x13D | 1 | | bNumConfigurations |
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+-----------+--------+------------+---------------------------------------------------+
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| 0x13E | 1 | | bNumInterfaces |
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+-----------+--------+------------+---------------------------------------------------+
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The following four commands have a common basic header called
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'usbip_header_basic', and their headers, called 'usbip_header' (before
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transfer_buffer payload), have the same length, therefore paddings are needed.
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usbip_header_basic:
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+-----------+--------+---------------------------------------------------+
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| Offset | Length | Description |
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+===========+========+===================================================+
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| 0 | 4 | command |
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+-----------+--------+---------------------------------------------------+
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| 4 | 4 | seqnum: sequential number that identifies requests|
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| | | and corresponding responses; |
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| | | incremented per connection |
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+-----------+--------+---------------------------------------------------+
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| 8 | 4 | devid: specifies a remote USB device uniquely |
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| | | instead of busnum and devnum; |
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| | | for client (request), this value is |
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| | | ((busnum << 16) | devnum); |
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| | | for server (response), this shall be set to 0 |
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+-----------+--------+---------------------------------------------------+
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| 0xC | 4 | direction: |
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| | | |
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| | | - 0: USBIP_DIR_OUT |
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| | | - 1: USBIP_DIR_IN |
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| | | |
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| | | only used by client, for server this shall be 0 |
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+-----------+--------+---------------------------------------------------+
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| 0x10 | 4 | ep: endpoint number |
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| | | only used by client, for server this shall be 0; |
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| | | for UNLINK, this shall be 0 |
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+-----------+--------+---------------------------------------------------+
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USBIP_CMD_SUBMIT:
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Submit an URB
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+-----------+--------+---------------------------------------------------+
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| Offset | Length | Description |
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+===========+========+===================================================+
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| 0 | 20 | usbip_header_basic, 'command' shall be 0x00000001 |
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+-----------+--------+---------------------------------------------------+
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| 0x14 | 4 | transfer_flags: possible values depend on the |
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| | | URB transfer_flags (refer to URB doc in |
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| | | Documentation/driver-api/usb/URB.rst) |
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| | | but with URB_NO_TRANSFER_DMA_MAP masked. Refer to |
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| | | function usbip_pack_cmd_submit and function |
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| | | tweak_transfer_flags in drivers/usb/usbip/ |
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| | | usbip_common.c. The following fields may also ref |
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| | | to function usbip_pack_cmd_submit and URB doc |
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+-----------+--------+---------------------------------------------------+
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| 0x18 | 4 | transfer_buffer_length: |
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| | | use URB transfer_buffer_length |
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+-----------+--------+---------------------------------------------------+
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| 0x1C | 4 | start_frame: use URB start_frame; |
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| | | initial frame for ISO transfer; |
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| | | shall be set to 0 if not ISO transfer |
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+-----------+--------+---------------------------------------------------+
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| 0x20 | 4 | number_of_packets: number of ISO packets; |
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| | | shall be set to 0xffffffff if not ISO transfer |
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+-----------+--------+---------------------------------------------------+
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| 0x24 | 4 | interval: maximum time for the request on the |
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| | | server-side host controller |
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+-----------+--------+---------------------------------------------------+
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| 0x28 | 8 | setup: data bytes for USB setup, filled with |
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| | | zeros if not used. |
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+-----------+--------+---------------------------------------------------+
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| 0x30 | n | transfer_buffer. |
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| | | If direction is USBIP_DIR_OUT then n equals |
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| | | transfer_buffer_length; otherwise n equals 0. |
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| | | For ISO transfers the padding between each ISO |
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| | | packets is not transmitted. |
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+-----------+--------+---------------------------------------------------+
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| 0x30+n | m | iso_packet_descriptor |
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+-----------+--------+---------------------------------------------------+
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USBIP_RET_SUBMIT:
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Reply for submitting an URB
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+-----------+--------+---------------------------------------------------+
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| Offset | Length | Description |
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+===========+========+===================================================+
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| 0 | 20 | usbip_header_basic, 'command' shall be 0x00000003 |
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+-----------+--------+---------------------------------------------------+
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| 0x14 | 4 | status: zero for successful URB transaction, |
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| | | otherwise some kind of error happened. |
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+-----------+--------+---------------------------------------------------+
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| 0x18 | 4 | actual_length: number of URB data bytes; |
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| | | use URB actual_length |
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+-----------+--------+---------------------------------------------------+
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| 0x1C | 4 | start_frame: use URB start_frame; |
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| | | initial frame for ISO transfer; |
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| | | shall be set to 0 if not ISO transfer |
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+-----------+--------+---------------------------------------------------+
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| 0x20 | 4 | number_of_packets: number of ISO packets; |
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| | | shall be set to 0xffffffff if not ISO transfer |
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+-----------+--------+---------------------------------------------------+
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| 0x24 | 4 | error_count |
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+-----------+--------+---------------------------------------------------+
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| 0x28 | 8 | padding, shall be set to 0 |
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+-----------+--------+---------------------------------------------------+
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| 0x30 | n | transfer_buffer. |
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| | | If direction is USBIP_DIR_IN then n equals |
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| | | actual_length; otherwise n equals 0. |
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| | | For ISO transfers the padding between each ISO |
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| | | packets is not transmitted. |
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+-----------+--------+---------------------------------------------------+
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| 0x30+n | m | iso_packet_descriptor |
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+-----------+--------+---------------------------------------------------+
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USBIP_CMD_UNLINK:
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Unlink an URB
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+-----------+--------+---------------------------------------------------+
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| Offset | Length | Description |
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+===========+========+===================================================+
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| 0 | 20 | usbip_header_basic, 'command' shall be 0x00000002 |
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+-----------+--------+---------------------------------------------------+
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| 0x14 | 4 | unlink_seqnum, of the SUBMIT request to unlink |
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+-----------+--------+---------------------------------------------------+
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| 0x18 | 24 | padding, shall be set to 0 |
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+-----------+--------+---------------------------------------------------+
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USBIP_RET_UNLINK:
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Reply for URB unlink
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+-----------+--------+---------------------------------------------------+
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| Offset | Length | Description |
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+===========+========+===================================================+
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| 0 | 20 | usbip_header_basic, 'command' shall be 0x00000004 |
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+-----------+--------+---------------------------------------------------+
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| 0x14 | 4 | status: This is similar to the status of |
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| | | USBIP_RET_SUBMIT (share the same memory offset). |
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| | | When UNLINK is successful, status is -ECONNRESET; |
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| | | when USBIP_CMD_UNLINK is after USBIP_RET_SUBMIT |
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| | | status is 0 |
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+-----------+--------+---------------------------------------------------+
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| 0x18 | 24 | padding, shall be set to 0 |
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+-----------+--------+---------------------------------------------------+
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EXAMPLE
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|
=======
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The following data is captured from wire with Human Interface Devices (HID)
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|
payload
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|
|
::
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CmdIntrIN: 00000001 00000d05 0001000f 00000001 00000001 00000200 00000040 ffffffff 00000000 00000004 00000000 00000000
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CmdIntrOUT: 00000001 00000d06 0001000f 00000000 00000001 00000000 00000040 ffffffff 00000000 00000004 00000000 00000000
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ffffffff860008a784ce5ae212376300000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
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RetIntrOut: 00000003 00000d06 00000000 00000000 00000000 00000000 00000040 ffffffff 00000000 00000000 00000000 00000000
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RetIntrIn: 00000003 00000d05 00000000 00000000 00000000 00000000 00000040 ffffffff 00000000 00000000 00000000 00000000
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ffffffff860011a784ce5ae2123763612891b1020100000400000000000000000000000000000000000000000000000000000000000000000000000000000000
|