168 lines
5.5 KiB
Groff
168 lines
5.5 KiB
Groff
.\" $NetBSD: mtio.4,v 1.16 2004/05/11 22:42:47 wiz Exp $
|
|
.\"
|
|
.\" Copyright (c) 1983, 1991, 1993
|
|
.\" The Regents of the University of California. 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.
|
|
.\" 3. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 REGENTS OR CONTRIBUTORS 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.
|
|
.\"
|
|
.\" from: @(#)mtio.4 8.1 (Berkeley) 6/5/93
|
|
.\"
|
|
.Dd January 14, 1999
|
|
.Dt MTIO 4
|
|
.Os
|
|
.Sh NAME
|
|
.Nm mtio
|
|
.Nd generic magnetic tape I/O interface
|
|
.Sh SYNOPSIS
|
|
.In sys/ioctl.h
|
|
.In sys/types.h
|
|
.In sys/mtio.h
|
|
.Sh DESCRIPTION
|
|
Magnetic tape has been the computer system backup and data transfer
|
|
medium of choice for decades, because it has historically been
|
|
cheaper in cost per bit stored, and the formats have been designed
|
|
for portability and storage.
|
|
However, tape drives have generally been the slowest mass
|
|
storage devices attached to any computer system.
|
|
.Pp
|
|
Magnetic tape comes in a wide variety of formats, from classic 9-track,
|
|
through various Quarter Inch Cartridge
|
|
.Pq Tn QIC
|
|
variants, to more modern systems using 8mm video tape, and
|
|
Digital Audio Tape
|
|
.Pq Tn DAT .
|
|
There have also been a variety of proprietary tape systems, including
|
|
.Tn DECtape ,
|
|
and
|
|
.Tn "IBM 3480" .
|
|
.Ss UNIX TAPE I/O
|
|
Regardless of the specific characteristics of the particular tape
|
|
transport mechanism (tape drive),
|
|
.Ux
|
|
tape I/O has two interfaces:
|
|
.Qq block
|
|
and
|
|
.Qq raw .
|
|
I/O through the block interface of a tape device is similar to I/O
|
|
through the block special device for a disk driver: the individual
|
|
.Xr read 2
|
|
and
|
|
.Xr write 2
|
|
calls can be done in any amount of bytes, but all data is buffered
|
|
through the system buffer cache, and I/O to the device is done in
|
|
1024 byte sized blocks.
|
|
This limitation is sufficiently restrictive that the block interface
|
|
to tape devices is rarely used.
|
|
.Pp
|
|
The
|
|
.Qq raw
|
|
interface differs in that all I/O can be done in arbitrary sized blocks,
|
|
within the limitations for the specific device and device driver,
|
|
and all I/O is synchronous.
|
|
This is the most flexible interface, but since there is very little
|
|
that is handled automatically by the kernel, user programs must
|
|
implement specific magnetic tape handling routines, which puts the onus
|
|
of correctness on the application programmer.
|
|
.Ss DEVICE NAME CONVENTIONS
|
|
Each magnetic tape subsystem has a couple of special devices
|
|
associated with it.
|
|
.Pp
|
|
The block device is usually named for the driver, e.g.
|
|
.Pa /dev/st0
|
|
for unit zero of a
|
|
.Xr st 4
|
|
.Tn SCSI
|
|
tape drive.
|
|
.Pp
|
|
The raw device name is the block device name with an
|
|
.Qq r
|
|
prepended, e.g.
|
|
.Pa /dev/rst0 .
|
|
.Pp
|
|
By default, the tape driver will rewind the tape drive when the
|
|
device is closed.
|
|
To make it possible for multiple program invocations to
|
|
sequentially write multiple files on the same tape, a
|
|
.Qq no rewind on close
|
|
device is provided, denoted by the letter
|
|
.Qq n
|
|
prepended to the name of the device, e.g.
|
|
.Pa /dev/nst0 ,
|
|
.Pa /dev/nrst0 .
|
|
.Pp
|
|
The
|
|
.Xr mt 1
|
|
command can be used to explicitly rewind, or otherwise position a
|
|
tape at a particular point with the no-rewind device.
|
|
.Ss FILE MARK HANDLING
|
|
Two end-of-file (EOF) markers mark the end of a tape (EOT), and
|
|
one end-of-file marker marks the end of a tape file.
|
|
.Pp
|
|
By default, the tape driver will write two End Of File (EOF) marks
|
|
and rewind the tape when the device is closed after the last write.
|
|
.Pp
|
|
If the tape is not to be rewound it is positioned with the
|
|
head in between the two tape marks, where the next write
|
|
will over write the second end-of-file marker.
|
|
.Pp
|
|
All of the magnetic tape devices may be manipulated with the
|
|
.Xr mt 1
|
|
command.
|
|
.Pp
|
|
A number of
|
|
.Xr ioctl 2
|
|
operations are available on raw magnetic tape.
|
|
Please see
|
|
.Aq Pa sys/mtio.h
|
|
for their definitions.
|
|
.\" The following definitions are from
|
|
.\" .Aq Pa sys/mtio.h :
|
|
.\" .Bd -literal
|
|
.\" there was a copy of sys/mtio.h here. silly.
|
|
.\" .Ed
|
|
.Pp
|
|
The manual pages for specific tape device drivers should list their
|
|
particular capabilities and limitations.
|
|
.Sh SEE ALSO
|
|
.Xr dd 1 ,
|
|
.Xr mt 1 ,
|
|
.Xr pax 1 ,
|
|
.Xr tar 1 ,
|
|
.Xr st 4 ,
|
|
.Xr wt 4
|
|
.Sh HISTORY
|
|
The
|
|
.Nm
|
|
manual appeared in
|
|
.Bx 4.2 .
|
|
.Sh BUGS
|
|
The status should be returned in a device independent format.
|
|
.Pp
|
|
If and when
|
|
.Nx
|
|
is updated to deal with non-512 byte per sector disk media through the
|
|
system buffer cache, perhaps a more sane tape interface can be
|
|
implemented.
|