term% ls -F
term% cat index.txt
USBD(4)                    Kernel Interfaces Manual                    USBD(4)

       usbd - Universal Serial Bus daemon

       usbd [ -Dd ] [ -s srv ] [ -m mnt ] [ hub...  ]

       Usbd complements usb(3) to provide USB I/O for device drivers.  It enu‐
       merates the bus, polling hub ports to detect device attachments and de‐
       tachments,  performs  initial  configuration  of  setup  endpoints, and
       writes extra information into usb(3) endpoint control  files,  to  ease
       device location.

       By  default, usbd opens all setup endpoints found at #u/usb (which cor‐
       respond to built-in hubs initialized by the kernel during boot).  Paths
       to  directories  representing  setup endpoints for hubs can be given as
       arguments to restrict usbd operation to such hubs.

       When a device is attached, depending upon a configuration file compiled
       into  usbd  , the appropriate device driver may be started without user
       intervention.  This mechanism can be used to statically link  some  USB
       device  drivers into usbd itself.  Initial configuration for setup end‐
       points is performed independently of this configuration.

       Usbd provides a file interface used to change debugging flags, and also
       used  by  USB  device drivers statically linked into usbd.  By default,
       the file system is mounted (after) at  /dev  and  a  9P  connection  is
       posted at /srv/usb.

       Besides  files  provided  by device drivers, the file usbdctl is always
       present in the file interface.  It accepts these control requests:

       debug n
              Sets the debugging level to n.

       fsdebug n
              Sets the file system debugging level to n.

       dump   Prints the list of devices and file systems known by usbd.

       Usbd recognizes the following options:

       -d     Print debugging diagnostics.   Repeating  the  option  increases

       -D     Print debugging diagnostics for the file system interface.

       -m mnt Mount the served file system at mnt.

       -s srv Post a 9P connection at #s/srv.

       Usbd  can  be  configured  to start drivers for devices matching one or
       more CSPs (hex representation of USB  class,  subclass  and  protocol),
       class,  subclass, protocol, vendor id, or device id.  When a new device
       is attached, usbd scans the configuration and, if an entry matches  the
       device  descriptor, starts the driver.  If no driver is configured, the
       setup endpoint for the device is left configured to let the user  start
       the driver by hand.

       Configuration is via compilation because one of the options is to embed
       (link) the driver into the usbd binary.  If  the  driver  is  embedded,
       usbd  creates  a process for it and calls its main entry point.  Other‐
       wise, usbd tries to locate the driver binary in /bin/usb and creates  a
       process to execute it.

       The  configuration file, usbdb, has two sections: embed and auto.  Each
       section includes lines to configure particular drivers.  A  driver  may
       have  more  than one line if necessary.  Each line includes the name of
       the driver (the base name of the binary) and one or more attributes  of
       the form


       The following attributes exist:

       class  Value  may  be the name of the class or a number identifying the
              device class (using C syntax).  The following  class  names  are
              known: audio, comms, hid, printer, storage, hub, and data.

              Value is the number of the device subclass.

       proto  Value is the number of the device protocol.

       csp    Value  is  the hexadecimal number describing the CSP for the de‐

       vid    Value is the vendor id.

       did    Value is the device id.

       args   This must be the last field.  The value is the rest of the line,
              and is supplied as arguments to the driver process.

       Several  environment  variables  can  be used to alter the behaviour of
       usbd, for example, for use in  plan9.ini(8).   usbdebug  sets  a  debug
       level  (zero for no diagnostics and positive values for increasing ver‐
       bosity).  kbargs overrides the keyboard arguments as specified  by  the
       configuration  file.  diskargs overrides the disk arguments in the same

       This configuration file links usb/kb into usbd when it is compiled.  It
       arranges  for  the  driver's  entry  point,  kbmain in this case, to be
       called for any device with CSPs matching either 0x010103  or  0x020103.
       Option  -d will be supplied as command line arguments for kbmain.  This
       configuration also arranges for /bin/usb/disk to start (with  no  argu‐
       ments) whenever a device of class storage is attached.

                   kb   csp=0x010103 csp=0x020103     args=-d
                   disk class=storage  args=

              9P connection to the driver file system.

       /dev   mount point for the driver file system.

              Configuration file deciding which devices are included into usbd
              and which ones are started automatically.


       usb(2), usb(3), usb(4)

       Usbd is not supposed to be restarted.  This is arguable.

       Not heavily exercised yet.