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.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)