ref: 20b9326daddd52ffe534a968fb596af1674f53cc
dir: /sys/man/3/0intro/
.TH INTRO 3
.SH NAME
intro \- introduction to the Plan 9 devices
.SH DESCRIPTION
A Plan 9
.I device
implements a file tree for client processes.
A file name beginning with a pound sign, such as
.LR #c ,
names the root of a file tree implemented by
a particular
.IR "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
.IP
.EX
bind("#c", "/dev", MREPL)
.EE
.LP
an
.IR ls (1)
of
.B /dev
will list the files provided by the
.I console
device.
.PP
A kernel device driver is a
.I 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
.RI ( Nop ,
.IR Session ,
.IR Flush ,
and
.IR Error )
have no subroutine equivalents.
.PP
When a system call is passed a file name beginning with
.L "#"
it looks at the next character, and if that is a valid
.I device character
it performs an
.IR 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
.L "/"
or end of string, those characters are passed as parameter
.I aname
to the attach. For example,
.IP
.EX
#I2
.EE
.PP
identifies the number 2 IP protocol stack
(see
.IR ip (3)).
.PP
Each kernel device has a conventional place at which to be bound
to the name space.
The
.I SYNOPSIS
sections of the following pages includes a
.I bind
command to put the device in the conventional place.
Most of these binds are done automatically by
.IR init (8)
using
.B newns
(see
.IR auth (2))
on the file
.B /lib/namespace
(see
.IR namespace (6)).
When typed to
.IR rc (1),
the
.I bind
commands will need quotes to protect the
.B #
characters.
.SH SEE ALSO
.IR intro (5),
.IR intro (2)