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diff --git a/share/man/man4/intro.4 b/share/man/man4/intro.4 new file mode 100644 index 000000000000..93a9ab59d25d --- /dev/null +++ b/share/man/man4/intro.4 @@ -0,0 +1,178 @@ +.\" +.\" 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. +.\" +.\" $FreeBSD$ +.\" +.Dd January 20, 1996 +.Dt INTRO 4 +.Os +.Sh NAME +.Nm intro +.Nd introduction to devices and device drivers +.Sh DESCRIPTION +This section contains information related to devices, device drivers +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 terminal devices is likely to be not useful at all. +.Ss Accessing Devices +Most of the devices in a +.Ux Ns +-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 +(see also +.Xr hier 7 ) . +.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 +.Er 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 to use better terms, buffered and unbuffered +(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 and, for historical reasons, 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 letter +.Ql r +to the path name of the device node, for example +.Pa /dev/rda0 +denotes the raw device for the first SCSI disk, while +.Pa /dev/da0 +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 +(i.e., those used like tapes). +.Pp +Access restrictions to device nodes are usually subject to the regular +file permissions of the device node entry, instead of being enforced +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 +(for the +.Em i386 +architecture). +.Sh SEE ALSO +.Xr close 2 , +.Xr ioctl 2 , +.Xr mmap 2 , +.Xr open 2 , +.Xr read 2 , +.Xr select 2 , +.Xr socket 2 , +.Xr write 2 , +.Xr devfs 5 , +.Xr hier 7 , +.Xr config 8 +.Sh HISTORY +This manual page first appeared in +.Fx 2.1 . +.Sh AUTHORS +.An -nosplit +This man page has been written by +.An J\(:org Wunsch +with initial input by +.An David E. O'Brien . |