mirror of
https://github.com/freebsd/freebsd-src.git
synced 2024-11-30 21:43:34 +00:00
Add intro(4), as it's being referenced from severall other pages.
Closes PR # docs/947: missing intro(4) manpage Submitted by: David E. O'Brien (initial version)
This commit is contained in:
Joerg Wunsch
parent
85373d20b1
commit
f00e21badf
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=13531
175
share/man/man4/intro.4
Normal file
175
share/man/man4/intro.4
Normal file
@ -0,0 +1,175 @@
|
||||
.\"
|
||||
.\" Copyright (c) 1996 David E. O'Brien, Joerg Wunsch
|
||||
.\"
|
||||
.\" All rights reserved.
|
||||
.\"
|
||||
.\" Redistribution and use in source and binary forms, with or without
|
||||
.\" modification, are permitted provided that the following conditions
|
||||
.\" are met:
|
||||
.\" 1. Redistributions of source code must retain the above copyright
|
||||
.\" notice, this list of conditions and the following disclaimer.
|
||||
.\" 2. Redistributions in binary form must reproduce the above copyright
|
||||
.\" notice, this list of conditions and the following disclaimer in the
|
||||
.\" documentation and/or other materials provided with the distribution.
|
||||
.\"
|
||||
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
|
||||
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
|
||||
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
|
||||
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
|
||||
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
|
||||
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
|
||||
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
|
||||
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
|
||||
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
|
||||
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
|
||||
.\"
|
||||
.\" $Id$
|
||||
.\"
|
||||
.Dd January 20, 1996
|
||||
.Dt INTRO 4
|
||||
.Os FreeBSD 2.1
|
||||
.Sh NAME
|
||||
.Nm intro
|
||||
.Nd introduction to devices and device drivers
|
||||
.Sh DESCRIPTION
|
||||
This section contains information related to devices, device driver
|
||||
and miscellaneous hardware.
|
||||
.Ss The device abstraction
|
||||
Device is a term used mostly for hardware-related stuff that belongs
|
||||
to the system, like disks, printers, or a graphics display with its
|
||||
keyboard. There are also so-called
|
||||
.Em pseudo-devices
|
||||
where a device driver emulates the behaviour of a device in software
|
||||
without any particular underlying hardware. A typical example for
|
||||
the latter class is
|
||||
.Pa /dev/mem ,
|
||||
a loophole where the physical memory can be accessed using the regular
|
||||
file access semantics.
|
||||
.Pp
|
||||
The device abstraction generally provides a common set of system calls
|
||||
layered on top of them, which are dispatched to the corresponding
|
||||
device driver by the upper layers of the kernel. The set of system
|
||||
calls available for devices is chosen from
|
||||
.Xr open 2 ,
|
||||
.Xr close 2 ,
|
||||
.Xr read 2 ,
|
||||
.Xr write 2 ,
|
||||
.Xr ioctl 2 ,
|
||||
.Xr select 2 ,
|
||||
and
|
||||
.Xr mmap 2 .
|
||||
Not all drivers implement all system calls, for example, calling
|
||||
.Xr mmap 2
|
||||
on a terminal devices is likely to be not useful at all.
|
||||
.Ss Accessing Devices
|
||||
Most of the devices in a unix-like operating system are accessed
|
||||
through so-called
|
||||
.Em device nodes ,
|
||||
sometimes also called
|
||||
.Em special files .
|
||||
They are usually located under the directory
|
||||
.Pa /dev
|
||||
in the file system hierarchy
|
||||
.Pq see also Xr hier 7 .
|
||||
.Pp
|
||||
Until
|
||||
.Xr devfs 5
|
||||
is fully functional, each device node must be created statically and
|
||||
independently of the existence of the associated device driver,
|
||||
usually by running
|
||||
.Xr MAKEDEV 8 .
|
||||
.Pp
|
||||
Note that this could lead to an inconsistent state, where either there
|
||||
are device nodes that do not have a configured driver associated with
|
||||
them, or there may be drivers that have successfully probed for their
|
||||
devices, but cannot be accessed since the corresponding device node is
|
||||
still missing. In the first case, any attempt to reference the device
|
||||
through the device node will result in an error, returned by the upper
|
||||
layers of the kernel, usually
|
||||
.Ql ENXIO .
|
||||
In the second case, the device node needs to be created before the
|
||||
driver and its device will be usable.
|
||||
.Pp
|
||||
Some devices come in two flavors:
|
||||
.Em block
|
||||
and
|
||||
.Em character
|
||||
devices, or by a better name, buffered and unbuffered
|
||||
.Pq raw
|
||||
devices. The traditional names are reflected by the letters
|
||||
.Ql b
|
||||
and
|
||||
.Ql c
|
||||
as the file type identification in the output of
|
||||
.Ql ls -l .
|
||||
Buffered devices are being accessed through the buffer cache of the
|
||||
operating system, and they are solely intended to layer a file system
|
||||
on top of them. They are normally implemented for disks and disk-like
|
||||
devices only, for historical reasons also for tape devices.
|
||||
.Pp
|
||||
Raw devices are available for all drivers, including those that also
|
||||
implement a buffered device. For the latter group of devices, the
|
||||
differentiation is conventionally done by prepending the latter
|
||||
.Ql r
|
||||
to the path name of the device node, for example
|
||||
.Pa /dev/rsd0
|
||||
denotes the raw device for the first SCSI disk, while
|
||||
.Pa /dev/sd0
|
||||
is the corresponding device node for the buffered device.
|
||||
.Pp
|
||||
Unbuffered devices should be used for all actions that are not related
|
||||
to file system operations, even if the device in question is a disk
|
||||
device. This includes making backups of entire disk partitions, or
|
||||
to
|
||||
.Em raw
|
||||
floppy disks
|
||||
.Pq i.e. those used like tapes .
|
||||
.Pp
|
||||
Access restrictions to device nodes are usually subject of the regular
|
||||
file permissions of the device node entry, instead of being implied
|
||||
directly by the drivers in the kernel.
|
||||
.Ss Drivers without device nodes
|
||||
Drivers for network devices do not use device nodes in order to be
|
||||
accessed. Their selection is based on other decisions inside the
|
||||
kernel, and instead of calling
|
||||
.Xr open 2 ,
|
||||
use of a network device is generally introduced by using the system
|
||||
call
|
||||
.Xr socket 2 .
|
||||
.Ss Configuring a driver into the kernel
|
||||
For each kernel, there is a configuration file that is used as a base
|
||||
to select the facilities and drivers for that kernel, and to tune
|
||||
several options. See
|
||||
.Xr config 8
|
||||
for a detailed description of the files involved. The individual
|
||||
manual pages in this section provide a sample line for the
|
||||
configuration file in their synopsis portion. See also the sample
|
||||
config file
|
||||
.Pa /sys/i386/conf/LINT
|
||||
.Po
|
||||
for the
|
||||
.Em i386
|
||||
architecture
|
||||
.Pc .
|
||||
.Sh SEE ALSO
|
||||
.Xr open 2 ,
|
||||
.Xr close 2 ,
|
||||
.Xr read 2 ,
|
||||
.Xr write 2 ,
|
||||
.Xr ioctl 2 ,
|
||||
.Xr select 2 ,
|
||||
.Xr mmap 2 ,
|
||||
.Xr socket 2 ,
|
||||
.Xr hier 7 ,
|
||||
.Xr config 8 ,
|
||||
.Xr MAKEDEV 7 ,
|
||||
.Xr devfs 5 Pq not yet existent .
|
||||
.Sh AUTHORS
|
||||
This man page has been written by
|
||||
.if t J\(:org Wunsch
|
||||
.if n Joerg Wunsch
|
||||
with initial input by David E. O'Brien.
|
||||
.Sh HISTORY
|
||||
.Nm intro
|
||||
appeared in FreeBSD 2.1.
|
||||
|
||||
Loading…
Reference in New Issue
Block a user