Manual page for ST(4)
st - SCSI Tape Device Driver
SYNOPSIS
device_name as st0/1 at sc0 target ? lun ?
DESCRIPTION
This driver allows access to a number of tape drives with standard SCSI
interfaces. Four different devices in /dev access this driver:
-
/dev/rst? Generic SCSI tape, rewind on close
/dev/nrst? Generic SCSI tape, no rewind on close
/dev/rxt? Exabyte SCSI tape, rewind on close
/dev/nrxt? Exabyte SCSI tape, no rewind on close
All four of these devices are character devices. There is no block I/O to
tape on the NeXT machine. The Exabyte has its own device entry because it
has unusual initialization requirements that are performed implicitly by
the driver when /dev/rxt? or /dev/nrxt? is opened.
Tape operation occurs in two basic modes - fixed block size and variable
block size. In this context, a "block" refers to one record on the tape.
Some tape drives can write blocks of arbitrary length; others require a
constant block size. Ioctl() calls are provided to set the appropriate
mode. In the case of fixed block mode, if a write() occurs with a byte
count which is not an integral multiple of the block size, the last partial
block written will be padded with zeroes to make a complete block. The
default mode for the st driver is variable block mode.
The following operations are allowed by the SCSI tape driver:
- open()
-
See open(2).
- close()
-
Closing a SCSI tape devices has some implied effects. If the last
operation on the device was a write(), a tape mark is written during
the close operation. If the tape device is /dev/rst? or /dev/rxt?, the
tape will be rewound to beginning of tape (BOT) during the close operation.
- read()
-
See read(2).
- write()
-
See write(2). This operation is not legal at all times; for example, after
reading a portion of a tape, a write command is illegal if more data exists
on the tape. One can only write to a tape if the tape is at BOT or at the
end of recorded data.
- ioctl()
-
The general form of an ioctl() call is
-
ioctl(int d, u_int request, char *argp)
The following ioctl requests are currently defined
(see /NextDeveloper/Headers/bsd/dev/scsireg.h and /NextDeveloper/Headers/bsd/sys/mtio.h):
- MTIOCFIXBLK
-
Sets the driver to fixed block mode. argp points to
an int containing the desired block size.
- MTIOCVARBLK
-
Set variable block mode. *argp is undefined. This mode
is the default mode.
- MTIOCMODSEL
-
Executes a mode select command. argp points to
struct modesel_parms (see /NextDeveloper/Headers/bsd/dev/scsireg.h). Mode select
and Mode Sense command are largely vendor unique SCSI
implementations.
- MTIOCMODSEN
-
Executes a mode sense command. argp points to
struct modesel_parms (see /NextDeveloper/Headers/bsd/dev/scsireg.h).
- MTIOCINILL
-
Inhibit illegal length. This causes the "suppress Illegal
length" bit to be set on all SCSI read commands. This
allows reading variable block sizes without knowing
the block size (and without receiving error status
from the drive when doing so). This is the default mode for
the Exabyte device (/dev/rxt? and /dev/nrxt?).
- MTIOCALILL
-
Allow illegal length. This causes error status (EIO) to
result when the number of bytes requested in a read
operation does not equal the number of bytes actually in
the block to be read. This is the default mode for the
non-Exabyte device (/dev/rst? and /dev/nrst?).
- MTIOCSRQ
-
Execute an arbitrary SCSI command using the scsi_req
mechanism.
argp points to a struct scsi_req, which is defined in
/NextDeveloper/Headers/bsd/dev/scsireg.h as are all other constants used with
this mechanism. This struct contains both the input to the
st driver required for execution of a command (SCSI CDB
bytes, address at which DMA will occur, etc.) as well as
the status block upon return.
For MTIOCSRQ, the following status is provided:
- srp->sr_io_status
-
Indicates success, I/O timeout, SCSI
check status, DMA overrun, etc.
- srp->sr_scsi_status
-
The actual SCSI status byte returned by the target.
- srp->sr_dma_xfr
-
Number of data bytes actually transferred to/from device.
- srp->sr_exec_time
-
Command execution time, with microsecond resolution.
FILES
/NextDeveloper/Headers/bsd/dev/scsireg.h
/NextDeveloper/Headers/bsd/sys/mtio.h
/dev/rst?
/dev/nrst?
/dev/rxt?
/dev/nrxt?
SEE ALSO
open(2), read(2), write(2), ioctl(2), close(2), dump(8)
BUGS
The default of variable block mode does not work for some older tape drives. Before these drives can be used,
the driver must be reconfigured
for the appropriate fixed block size
using the MTIOCFIXBLK ioctl.
Created by unroff & hp-tools.
© somebody (See intro for details). All Rights Reserved.
Last modified 11/5/97
