Hi All, Here is what I have in mind as usb redirection protocol:
USB redirerection protocol (draft) ---------------------------------- The protocol described in this document is meant for tunneling usb transfers to a single usb device. Note: not an entire hub, only a single device. The most significant use case for this is taking a usb device attached to some machine "a" which acts as a client / viewer to a virtual machine "v" hosted on another machine "b", and make the usb device show up inside the virtual machine as if it were attached directly to the virtual machine "v". The described protocol assumes a reliable ordered bidirectional transport is available, for example a tcp socket. Definitions: vm-host: machine running the virtual machine with the guest os accessing the usb device usb-host: machine which has the usb device which "appears" inside the vm Basic packet structure / communication -------------------------------------- Each packet exchanged between the vm-host and the usb-host starts with a usb_redir_header, followed by an optional command specific header follow by optional additional data. The usb_redir_header each packet starts with looks as follows: struct usb_redir_header { uint32_t command; uint32_t length; } command: A command code, from the command enum length: length of the optional command specific header + the optional additional data. Can be 0. There are 3 types of commands: 1) Connection setup commands 2) Synchroneous commands 3) Asynchroneous commands Given that everything is done over a potentially slow transport in practice the diferentiating between synchroneous and asynchroneous commands may seem odd. The difference is how the usb-host will handle them once received. For synchroneous commands the usb-host will hand the request over to the host os and then *wait* for a response. This means that the vm-host is guaranteed to get an "immediate" response. Where as for asynchroneous commands to usb-host hands the request over to the host os with the request to let the usb-host process know when the request is done. Also note that all synchroneous commands should only be executed when no asynchroneous commands are pending on the device / interface / endpoint affected by the synchroneous command. Any pending commands will get dropped, and any active iso streams / allocated bulk streams will get stopped / free-ed. Command list ------------ Connection setup commands: usb_redir_hello usb_redir_report_descriptor Synchroneous commands: usb_redir_set_configuration usb_redir_get_configuration usb_redir_configuration_status usb_redir_set_alt_setting usb_redir_get_alt_setting usb_redir_alt_setting_status usb_redir_start_iso_stream usb_redir_stop_iso_stream usb_redir_iso_stream_status usb_redir_alloc_bulk_streams usb_redir_free_bulk_streams usb_redir_bulk_streams_status Asynchroneous commands: usb_redir_control_packet usb_redir_bulk_packet usb_redir_iso_packet usb_redir_hello --------------- usb_redir_header.command: usb_redir_hello usb_redir_header.length: <see description> struct usb_redir_hello_header { char version[64]; uint32_t capabilities[0]; } No command specific additional data. A packet of this type is send by both sides as soon as a connection is establised. This commands consists of: version: A free form 0 terminated version string, useful for logging should not be parsed! Suggested format: "qemu 0.13", "usb-redir-daemon 0.1", etc. capabilities: A variable length array for announcing capabilities. The value of the length field depends on the size of the capabilities array. If we cross the 32 capabilities count, it will go from 1 uint32_t to 2, etc. the value is 64 + capabilities-array-size * sizeof(uint32_t). Currently the following capabilities are defined: usb_redir_cap_bulk_streams: USB 3 bulk streams are supported usb_redir_report_descriptor --------------------------- usb_redir_header.command: usb_redir_report_desciptor usb_redir_header.length: <sizeof usb device descriptors> No command specific header. The command specific additional data contains the entire descriptors for the usb device. A packet of this type is send by the usb-host directly after the hello packet it contains the usb descriptor tables for the usb device. usb_redir_set_configuration --------------------------- usb_redir_header.command: usb_redir_set_configuration usb_redir_header.length: sizeof(usb_redir_set_configuration_header) struct usb_redir_set_configuration_header { uint8_t configuration; } No command specific additional data. This command can be send by the vm-host to set (change) the active configuration of the usb device. usb_redir_get_configuration --------------------------- usb_redir_header.command: usb_redir_get_configuration usb_redir_header.length: 0 No command specific header. No command specific additional data. This command can be send by the vm-host to get (query) the active configuration of the usb device. usb_redir_configuration_status ------------------------------ usb_redir_header.command: usb_redir_configuration_status usb_redir_header.length: sizeof(usb_redir_configuration_status_header) struct usb_redir_configuration_status_header { uint8_t status; uint8_t configuration; } No command specific additional data. This command is send by the usb-host in response to a usb_redir_set_configuration/usb_redir_get_configuration command. It reports a status code and the active configuration after the command. usb_redir_set_alt_setting ------------------------- usb_redir_header.command: usb_redir_set_alt_setting usb_redir_header.length: sizeof(usb_redir_set_alt_setting_header) struct usb_redir_set_alt_setting_header { uint8_t interface; uint8_t alt; } No command specific additional data. This command can be send by the vm-host to set (change) the alt_setting of interface <interface> to <alt>. usb_redir_get_alt_setting --------------------------- usb_redir_header.command: usb_redir_get_alt_setting usb_redir_header.length: sizeof(usb_redir_get_alt_setting_header) struct usb_redir_get_alt_setting_header { uint8_t interface; } No command specific additional data. The command specific additional data is a single byte specifing the interface for which to get the alt setting. This command can be send by the vm-host to get (query) the active alt_setting of an interface of the usb device. usb_redir_alt_setting_status ---------------------------- usb_redir_header.command: usb_redir_alt_setting_status usb_redir_header.length: sizeof(usb_redir_alt_setting_status_header) struct usb_redir_alt_setting_status_header { uint8_t status; uint8_t interface; uint8_t alt; } No command specific additional data. This command is send by the usb-host in response to a usb_redir_set_alt_setting/usb_redir_get_alt_setting command. It reports a status code, the affected interface and the active alt_setting for that interface after the command. usb_redir_start_iso_stream -------------------------- usb_redir_header.command: usb_redir_start_iso_stream usb_redir_header.length: sizeof(usb_redir_start_iso_stream_header) struct usb_redir_start_iso_stream_header { uint8_t endpoint; uint8_t pkts_per_urb; uint8_t no_urbs; } No command specific additional data. This command can be send by the vm-host to start a iso stream on the designated endpoint of the usb device. This function allocates no_urbs urbs with pkts_per_urb iso packets/frames per urb. For iso input endpoints these urbs will get submitted to the device *immediately*, for iso output endpoints the usb-host will wait till it has received 1.5 * pkts_per_urb iso packets to fill its ring buffer before submitting the first urb. usb_redir_stop_iso_stream ------------------------- usb_redir_header.command: usb_redir_stop_iso_stream usb_redir_header.length: 1 No command specific header. The command specific additional data is a single byte specifing the endpoint on which to stop the stream. This command can be send by the vm-host to stop an iso stream on the designated endpoint. This will cancel all pending urbs, flush the usb-host's buffers and free all relevant resources. usb_redir_iso_stream_status --------------------------- usb_redir_header.command: usb_redir_iso_stream_status usb_redir_header.length: sizeof(usb_redir_iso_stream_status_header) struct usb_redir_alt_setting_status_header { uint8_t status; uint8_t endpoint; } No command specific additional data. This command is send by the usb-host in response to a usb_redir_start_iso_stream or usb_redir_stop_iso_stream command. Note that for the starting of output iso streams a success status only indicates that all the buffers were successfully allocated, the actual stream is not started until enough packets are buffered. Note that this can also be send unsolicited by a usb-host in case of an error with an iso output stream, see usb_redir_iso_packet. usb_redir_alloc_bulk_streams ---------------------------- usb_redir_header.command: usb_redir_alloc_bulk_streams usb_redir_header.length: sizeof(usb_redir_alloc_bulk_streams_header) struct usb_redir_alloc_bulk_streams_header { uint8_t endpoint; uint8_t no_streams; } No command specific additional data. This command can be send by the vm-host to the usb-host to request that the usb-host allocates IDs so the vm-host can use up to no_streams stream IDs. usb_redir_free_bulk_streams ---------------------------- usb_redir_header.command: usb_redir_free_bulk_streams usb_redir_header.length: sizeof(usb_redir_free_bulk_streams_header) struct usb_redir_free_bulk_streams_header { uint8_t endpoint; } No command specific additional data. This command can be send by the vm-host to the usb-host to free any bulk streams previouisly allocated on the endpoint. usb_redir_bulk_streams_status ----------------------------- usb_redir_header.command: usb_redir_bulk_streams_status usb_redir_header.length: sizeof(usb_redir_bulk_streams_status_header) struct usb_redir_bulk_streams_status_header { uint8_t status; uint8_t endpoint; uint8_t no_streams; } No command specific additional data. This command is send by the usb-host in response to a usb_redir_alloc_bulk_streams or usb_redir_free_bulk_streams command. Note that on a success status in response to a usb_redir_alloc_bulk_streams no_streams may be less then requested due to host controller / device limitations. On a success status in response to a usb_redir_alloc_bulk_streams the usb-host may use stream ids 1 through no_streams. usb_redir_control_packet ------------------------ usb_redir_header.command: usb_redir_control_packet usb_redir_header.length: sizeof(usb_redir_control_packet_header) + data_size struct usb_redir_control_packet_header { uint64_t pid; uint8_t endpoint; uint8_t request; uint8_t requesttype; uint8_t status; uint16_t value; uint16_t index; uint16_t data_size; } The additional data contains the control msg data to be send / received. Packets of this type initially get send by the vm-host to the usb-host. Where pid is a unique Packet ID to be able to match the async response from the usb-host to the original request. endpoint, request, requesttype, value and index have their standard meaning for usb control messages. status is only used when the usb-host sends its response, data_size is the amount of data the vm_host is sending / expects to read (in the USB_DIR_IN case). When the control msg has been processed by the device the usb device sends a usb_redir_control_packet back to the vm-host, with all fields unchanged except for the status field and data_size which get updated to match the actual results. Note how this packet only has additional data in one direction depending on the USB_DIR_IN flag of the requesttype. usb_redir_bulk_packet --------------------- usb_redir_header.command: usb_redir_bulk_packet usb_redir_header.length: sizeof(usb_redir_bulk_packet_header) + data_size struct usb_redir_bulk_packet_header { uint64_t pid; uint8_t endpoint; uint8_t status; uint16_t data_size; } The additional data contains the bulk msg data to be send / received. Packets of this type initially get send by the vm-host to the usb-host. Where pid is a unique Packet ID to be able to match the async response from the usb-host to the original request. data_size is the amount of data the vm_host is sending / expects to read (depending on the direction of the endpoint). When the bulk msg has been processed by the device the usb device sends a usb_redir_bulk_packet back to the vm-host, with the pid and endpoint fields unchanged and the status field and data_size updated to match the actual results. Note how this packet only has additional data in one direction depending on the direction of the endpoint. usb_redir_iso_packet -------------------- usb_redir_header.command: usb_redir_iso_packet usb_redir_header.length: sizeof(usb_redir_iso_packet_header) + data_size struct usb_redir_iso_packet_header { uint8_t endpoint; uint8_t status; uint16_t data_size; } The additional data contains the iso msg data to be send / received. Packets of this type should be send continuesly (at the endpoint interval speed) as soon as an iso stream is started using usb_redir_start_iso_stream the direction in which they gets send depends on the endpoints direction. The status field only has meaning for packets send from the usb-host to the vm-host (for iso input endpoints). Due to buffering it is not possibly to timely notify the vm-host of transfer errors for iso output packets. The usb-host will try to clear any error conditions itself. If it fails to do so it will send a usb_redir_iso_stream_status to the vm-host indicating there is a problem with the iso stream. ### Please let me know what you think of this. Thanks & Regards, Hans