0intro(3) [plan9 man page]

INTRO(3)						     Library Functions Manual							  INTRO(3)

NAME

       intro - introduction to the Plan 9 devices

DESCRIPTION

       A  Plan	9  device  implements a file tree for client processes.  A file name beginning with a pound sign, such as names the root of a file
       tree implemented by a particular kernel device driver identified by the character after the pound sign.	Such names are	usually  bound	to
       conventional locations in the name space.  For example, after

	      bind("#c", "/dev", MREPL)

       an ls(1) of /dev will list the files provided by the console device.

       A kernel device driver is a server in the sense of the Plan 9 File Protocol, 9P (see Section 5), but with the messages implemented by local
       rather than remote procedure calls.  Also, several of the messages (Nop, Session, Flush, and Error) have no subroutine equivalents.

       When a system call is passed a file name beginning with it looks at the next character, and if that is a valid device character it performs
       an  attach(5)  on  the corresponding device to get a channel representing the root of that device's file tree.  If there are any characters
       after the device character but before the next or end of string, those characters are passed as parameter aname to the attach.	For  exam-
       ple,

	      #Itcp

       identifies the implementation of the TCP protocol supplied by the IP device (see ip(3)).

       Each  kernel device has a conventional place at which to be bound to the name space.  The SYNOPSIS sections of the following pages includes
       a shell bind command to put the device in the conventional place.  Most of these binds are done automatically by init(8).

SEE ALSO

       intro(5), intro(2)

																	  INTRO(3)

DEVCTL(4)						   BSD Kernel Interfaces Manual 						 DEVCTL(4)

NAME

     devctl -- device event reporting and device control interface

DESCRIPTION

     The devctl device is used to report device events from the kernel.  Future versions will allow for some device control as well.

IMPLEMENTATION NOTES

     This design allows only one reader for /dev/devctl.  This is not desirable in the long run, but will get a lot of hair out of this implemen-
     tation.  Maybe we should make this device a clonable device.

     Also note: we specifically do not attach a device to the device_t tree to avoid potential chicken and egg problems.  One could argue that all
     of this belongs to the root node.	One could also further argue that the sysctl(3) interface that we have now might more properly be an
     ioctl(2) interface.

     SIGIO support is included in the driver.  However, the author is not sure that the SIGIO support is done correctly.  It was copied from a
     driver that had SIGIO support that likely has not been tested since FreeBSD 3.4 or FreeBSD 2.2.8!

     The read channel for this device is used to report changes to userland in realtime.  We return one record at a time.  If you try to read this
     device a character at a time, you will lose the rest of the data.	Listening programs are expected to cope.

     The sysctl and boot parameter hw.bus.devctl_disable is used to disable devctl when no devd(8) is running.

PROTOCOL

     The devctl device uses an ASCII protocol.	The driver returns one record at a time to its readers.  Each record is terminated with a newline.
     The first character of the record is the event type.

     Type    Description
     !	     A notify event, such as a link state change.
     +	     Device node in tree attached.
     -	     Device node in tree detached.
     ?	     Unknown device detected.

   Message Formats
     Except for the first character in the record, attach and detach messages have the same format.

	   Tdev at parent on location

     Part	 Description
     T		 + or -
     dev	 The device name that was attached/detached.
     parent	 The device name of the parent bus that attached the device.
     location	 Bus specific location information.

     The nomatch messages can be used to load devices driver.  If you load a device driver, then one of two things can happen.	If the device
     driver attaches to something, you will get a device attached message.  If it does not, then nothing will happen.

     The attach and detach messages arrive after the event.  This means one cannot use the attach message to load an alternate driver.	The attach
     message driver has already claimed this device.  One cannot use the detach messages to flush data to the device.  The device is already gone.

SEE ALSO

     devd(8)

BSD
								 February 11, 2003							       BSD