INTRO(3)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
#c,
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 example,
#I2
identifies the number 2 IP protocol stack
(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
bind
command to put the device in the conventional place.
Most of these binds are done automatically by
init(8)
using
newns
(see
auth(2))
on the file
/lib/namespace
(see
namespace(6)).
When typed to
rc(1),
the
bind
commands will need quotes to protect the
#
characters.
SEE
intro(5),
intro(2)