346 lines
11 KiB
Groff
346 lines
11 KiB
Groff
.\" $NetBSD: st.4,v 1.4 1997/10/08 09:55:33 kleink Exp $
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.\"
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.\" Copyright (c) 1996
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.\" Julian Elischer <julian@freebsd.org>. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\"
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Dd August 23, 1996
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.Dt ST 4
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.Os NetBSD
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.Sh NAME
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.Nm st
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.Nd SCSI tape driver
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.Sh SYNOPSIS
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.Cd st* at scsibus? target ? lun ?
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.Cd st1 at scsibus0 target 4 lun 0
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.Sh DESCRIPTION
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The
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.Nm
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driver provides support for
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.Tn SCSI
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tape drives. It allows a tape drive to be run in several different
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modes depending on minor numbers and supports several different
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`sub-modes'. The device can have both a
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.Em raw
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interface
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and a
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.Em block
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interface; however, only the raw interface is usually used (or
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recommended).
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.Pp
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.Tn SCSI
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devices have a relatively high level interface and talk to the
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system via a
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.Tn SCSI
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adapter and a
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.Tn SCSI
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adapter driver
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(e.g.,
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.Xr ahc 4 ) .
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A
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.Tn SCSI
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adapter must also be separately configured into the system before a
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.Tn SCSI
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tape can be configured.
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.Pp
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As the
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.Tn SCSI
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adapter is probed during boot, the
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.Tn SCSI
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bus is scanned for devices. Any devices found which answer as
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.Sq Em Sequential
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type devices will be attached to the
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.Nm
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driver.
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.Sh MOUNT SESSIONS
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The
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.Nm
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driver is based around the concept of a
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.Dq Em mount session ,
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which is defined as the period between the time that a tape is
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mounted, and the time when it is unmounted. Any parameters set
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during a mount session remain in effect for the remainder of the
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session or until replaced. The tape can be unmounted, bringing the
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session to a close in several ways. These include:
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.Bl -enum
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.It
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Closing an `unmount device', referred to as sub-mode 00 below. An
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example is
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.Pa /dev/rst0 .
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.It
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Using the MTOFFL
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.Xr ioctl 2
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command, reachable through the
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.Sq Cm offline
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command of
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.Xr mt 1 .
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.It
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Opening a different mode will implicitly unmount the tape, thereby
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closing off the mode that was previously mounted. All parameters
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will be loaded freshly from the new mode. (See below for more on
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modes.)
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.El
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.Sh MODES AND SUB-MODES
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There are several different
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.Sq operation
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modes. These are controlled by bits 2 and 3 of the minor number
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and are designed to allow users to easily read and write different
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formats of tape on devices that allow multiple formats. The
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parameters for each mode can be set individually by hand with the
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.Xr mt 1
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command. When a device corresponding to a particular mode is first
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mounted, The operating parameters for that mount session are copied
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from that mode. Further changes to the parameters during the
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session will change those in effect for the session but not those
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set in the operation mode. To change the parameters for an operation
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mode, one must compile them into the
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.Dq Em quirk
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table in the driver's source code.
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.Pp
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In addition to the operating modes mentioned above, bits 0 and 1
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of the minor number are interpreted as
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.Sq sub-modes .
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The sub-modes differ in the action taken when the device is closed:
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.Bl -tag -width XXXX
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.It 00
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A close will rewind the device; if the tape has been written, then
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a file mark will be written before the rewind is requested.
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The device is unmounted.
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.It 01
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A close will leave the tape mounted. If the tape was written to,
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a file mark will be written. No other head positioning takes place.
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Any further reads or writes will occur directly after the last
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read, or the written file mark.
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.It 10
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A close will rewind the device. If the tape has been written, then
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a file mark will be written before the rewind is requested. On
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completion of the rewind an unload command will be issued. The
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device is unmounted.
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.It 11
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Reserved. Currently unused.
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.El
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.Sh BLOCKING MODES
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.Tn SCSI
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tapes may run in either
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.Sq Em variable
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or
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.Sq Em fixed
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block-size modes. Most
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.Tn QIC Ns -type
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devices run in fixed block-size mode, where most nine-track tapes
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and many new cartridge formats allow variable block-size. The
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difference between the two is as follows:
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.Bl -inset
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.It Variable block-size:
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Each write made to the device results in a single logical record
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written to the tape. One can never read or write
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.Em part
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of a record from tape (though you may request a larger block and
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read a smaller record); nor can one read multiple blocks. Data
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from a single write is therefore read by a single read. The block
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size used may be any value supported by the device, the
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.Tn SCSI
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adapter and the system (usually between 1 byte and 64 Kbytes,
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sometimes more).
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.Pp
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When reading a variable record/block from the tape, the head is
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logically considered to be immediately after the last item read,
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and before the next item after that. If the next item is a file
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mark, but it was never read, then the next process to read will
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immediately hit the file mark and receive an end-of-file notification.
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.It Fixed block-size
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Data written by the user is passed to the tape as a succession of
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fixed size blocks. It may be contiguous in memory, but it is
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considered to be a series of independent blocks. One may never
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write an amount of data that is not an exact multiple of the
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blocksize. One may read and write the same data as a different
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set of records, In other words, blocks that were written together
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may be read separately, and vice-versa.
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.Pp
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If one requests more blocks than remain in the file, the drive will
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encounter the file mark. Because there is some data to return
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(unless there were no records before the file mark), the read will
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succeed, returning that data, The next read will return immediately
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with an EOF. (As above, if the file mark is never read, it remains
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for the next process to read if in no-rewind mode.)
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.El
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.Sh FILE MARK HANDLING
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The handling of file marks on write is automatic. If the user has
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written to the tape, and has not done a read since the last write,
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then a file mark will be written to the tape when the device is
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closed. If a rewind is requested after a write, then the driver
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assumes that the last file on the tape has been written, and ensures
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that there are two file marks written to the tape. The exception
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to this is that there seems to be a standard (which we follow, but
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don't understand why) that certain types of tape do not actually
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write two file marks to tape, but when read, report a `phantom'
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file mark when the last file is read. These devices include the
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QIC family of devices. (It might be that this set of devices is
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the same set as that of fixed block devices. This has not been
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determined yet, and they are treated as separate behaviors by the
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driver at this time.)
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.Sh KERNEL CONFIGURATION
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Because different tape drives behave differently, there is a
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mechanism within the source to
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.Nm
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to quickly and conveniently recognize and deal with brands and
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models of drive that have special requirements.
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.Pp
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There is a table (called the
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.Dq Em quirk table )
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in which the identification strings of known errant drives can be
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stored. Alongside each is a set of flags that allows the setting
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of densities and blocksizes for each of the modes, along with a
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set of `QUIRK' flags that can be used to enable or disable sections
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of code within the driver if a particular drive is recognized.
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.Sh IOCTLS
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The following
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.Xr ioctl 2
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calls apply to
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.Tn SCSI
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tapes. Some also apply to other tapes. They are defined in the
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header file
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.Aq Pa sys/mtio.h .
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.\"
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.\" Almost all of this discussion belongs in a separate mt(4)
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.\" manual page, since it is common to all magnetic tapes.
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.\"
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.Pp
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.Bl -tag -width MTIOCEEOT
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.It Dv MTIOCGET
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.Pq Li "struct mtget"
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Retrieve the status and parameters of the tape.
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.It Dv MTIOCTOP
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.Pq Li "struct mtop"
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Perform a multiplexed operation. The argument structure is as follows:
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.Bd -literal -offset indent
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struct mtop {
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short mt_op;
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daddr_t mt_count;
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};
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.Ed
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.Pp
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The following operation values are defined for
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.Va mt_op :
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.Bl -tag -width MTSELDNSTY
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.It Dv MTWEOF
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Write
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.Va mt_count
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end of file marks at the present head position.
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.It Dv MTFSF
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Skip over
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.Va mt_count
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file marks. Leave the head on the EOM side of the last skipped
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file mark.
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.It Dv MTBSF
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Skip
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.Em backwards
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over
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.Va mt_count
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file marks. Leave the head on the BOM (beginning of media)
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side of the last skipped file mark.
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.It Dv MTFSR
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Skip forwards over
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.Va mt_count
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records.
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.It Dv MTBSR
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Skip backwards over
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.Va mt_count
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records.
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.It Dv MTREW
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Rewind the device to the beginning of the media.
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.It Dv MTOFFL
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Rewind the media (and, if possible, eject). Even if the device cannot
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eject the media it will often no longer respond to normal requests.
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.It Dv MTNOP
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No-op; set status only.
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.It Dv MTCACHE
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Enable controller buffering.
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.It Dv MTNOCACHE
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Disable controller buffering.
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.It Dv MTSETBSIZ
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Set the blocksize to use for the device/mode. If the device is capable of
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variable blocksize operation, and the blocksize is set to 0, then the drive
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will be driven in variable mode. This parameter is in effect for the present
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mount session only.
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.It Dv MTSETDNSTY
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Set the density value (see
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.Xr mt 1 )
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to use when running in the mode opened (minor bits 2 and 3).
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This parameter is in effect for the present
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mount session only.
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.It Dv MTCMPRESS
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Enable or disable tape drive data compression. Typically tape drives will
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quite contentedly ignore settings on reads, and will probably keep you from
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changing density for writing anywhere but BOT.
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.El
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.It Dv MTIOCIEOT
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Set end-of-tape processing (not presently supported for
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.Nm
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devices).
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.It Dv MTIOCEEOT
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Set end-of-tape processing (not presently supported for
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.Nm
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devices).
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.It Dv MTIOCRDSPOS
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.Pq Li "u_int32_t"
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Read device logical block position. Not all drives support this option.
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.It Dv MTIOCRDHPOS
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.Pq Li "u_int32_t"
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Read device hardware block position. Not all drives support this option.
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.It Dv MTIOCSLOCATE
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.Pq Li "u_int32_t"
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Position the tape to the specified device logical block position.
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.It Dv MTIOCHLOCATE
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.Pq Li "u_int32_t"
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Position the tape to the specified hardware block position.
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Not all drives support this option.
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.El
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.Sh FILES
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.Bl -tag -width /dev/[n][e]rst[0-9] -compact
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.It Pa /dev/[n][e]rst[0-9]
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general form:
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.It Pa /dev/rst0
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Mode 0, rewind on close
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.It Pa /dev/nrst0
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Mode 2, No rewind on close
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.It Pa /dev/erst0
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Mode 3, Eject on close (if capable)
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.El
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.Sh DIAGNOSTICS
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None.
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.Sh SEE ALSO
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.Xr mt 1 ,
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.Xr scsi 4
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.Sh HISTORY
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This
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.Nm
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driver was originally written for
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.Tn Mach
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2.5 by Julian Elischer, and was ported to
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.Tn NetBSD
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by Charles Hannum. This man page was edited for
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.Tn NetBSD
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by Jon Buller.
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