LDP
/
man-pages
mirror of https://github.com/mkerrisk/man-pages
0
1
Fork 0
Code Releases Activity

Updates from Kai Makisara <Kai.Makisara@kolumbus.fi>, the author 

of the st driver.
This commit is contained in:
Michael Kerrisk 2005-04-05 12:20:49 +00:00
parent b6dd43ba57
commit e2af0daf4a
1 changed files with 106 additions and 56 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

162
man4/st.4
View File

@ -1,5 +1,5 @@
.\" Copyright 1995 Robert K. Nichols (Robert.K.Nichols@att.com)
.\" Copyright 1999 Kai Mäkisara (Kai.Makisara@metla.fi)
.\" Copyright 1999-2005 Kai Mäkisara (Kai.Makisara@kolumbus.fi)
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
@ -9,7 +9,7 @@
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
@ -17,10 +17,10 @@
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.TH ST 4 1999-01-18 "Linux 2.0 - 2.2" "Linux Programmer's Manual"
.TH ST 4 2005-03-13 "Linux 2.0 - 2.6" "Linux Programmer's Manual"
.SH NAME
st \- SCSI tape device
.SH SYNOPSIS
@ -44,10 +44,12 @@ driver uses major device number 9.
.PP
Each device uses eight minor device numbers. The lower-most five bits
in the minor numbers are assigned sequentially in the order of
detection. The minor numbers can be grouped into
detection. In the 2.6 kernel, the bits above the eight lower-most bits are
concatenated to the five lower-most bits to form the tape number.
The minor numbers can be grouped into
two sets of four numbers: the principal (auto-rewind) minor device numbers,
.IR n ,
and a \(lqno-rewind\(rq device numbers,
and the \(lqno-rewind\(rq device numbers,
.IR "" ( n "+ 128)."
Devices opened using the principal device number will be sent a
\s-1REWIND\s+1 command when they are closed.
@ -88,8 +90,8 @@ The driver uses an internal buffer that has to be large enough to hold
at least one tape block. In kernels before 2.1.121, the buffer is
allocated as one contiguous block. This limits the block size to the
largest contiguous block of memory the kernel allocator can provide.
The limit is currently 128 kB for the 32-bit architectures and
256 kB for the 64-bit architectures. In newer kernels the driver
The limit is currently 128 kB for 32-bit architectures and
256 kB for 64-bit architectures. In newer kernels the driver
allocates the buffer in several parts if necessary. By default, the
maximum number of parts is 16. This means that the maximum block size
is very large (2 MB if allocation of 16 blocks of 128 kB succeeds).
@ -104,8 +106,9 @@ too much on dynamic buffer allocation with kernels older than 2.1.121
.PP
The driver does not specifically support any tape drive brand or
model. After system start-up the tape device options are defined by
the drive firmware. For example, if the drive firmware selects fixed
block mode, the tape device uses fixed block mode. The options can
the drive firmware.
For example, if the drive firmware selects fixed-block mode,
the tape device uses fixed-block mode. The options can
be changed with explicit
.B ioctl()
calls and remain in effect when the device is closed and reopened.
@ -115,8 +118,8 @@ device.
Different options can be specified for the different devices within
the subgroup of four. The options take effect when the device is
opened. For example, the system administrator can define
one device that writes in fixed block mode with a certain block size,
and one which writes in variable block mode (if the drive supports
one device that writes in fixed-block mode with a certain block size,
and one which writes in variable-block mode (if the drive supports
both modes).
.PP
The driver supports
@ -137,31 +140,44 @@ Device
.B /dev/tape
is usually created as a hard or soft link to the default tape device
on the system.
.PP
Starting from kernel 2.6.2, the driver exports in the sysfs directory
.BR /sys/class/scsi_tape
the attached devices and some parameters assigned to the devices.
.SH "DATA TRANSFER"
The driver supports operation in both fixed block mode and variable
block mode (if supported by the drive). In fixed block mode the drive
The driver supports operation in both fixed-block mode and
variable-block mode (if supported by the drive).
In fixed-block mode the drive
writes blocks of the specified size and the block size is not
dependent on the byte counts of the write system calls. In variable
block mode one tape block is written for each write call and the byte
dependent on the byte counts of the write system calls.
In variable-block mode one tape block is written for each write call
and the byte
count determines the size of the corresponding tape block. Note that
the blocks on the tape do don't contain any information about the
the blocks on the tape don't contain any information about the
writing mode: when reading, the only important thing is to use
commands that accept the block sizes on the tape.
.PP
In variable block mode the read byte count does not have to match
In variable-block mode the read byte count does not have to match
the tape block size exactly. If the byte count is larger than the
next block on tape, the driver returns the data and the function
returns the actual block size. If the block size is larger than the
byte count, the requested amount of data from the start of the block
is returned and the rest of the block is discarded.
.PP
In fixed block mode the read byte counts can be arbitrary if
In fixed-block mode the read byte counts can be arbitrary if
buffering is enabled, or a multiple of the tape block size if
buffering is disabled. Kernels before 2.1.121 allow writes with
arbitrary byte count if buffering is enabled. In all other cases
(kernel before 2.1.121 with buffering disabled or newer kernel) the
write byte count must be a multiple of the tape block size.
.PP
In the 2.6 kernel, the driver tries to use direct transfers between the user
buffer and the device. If this is not possible, the driver's internal buffer
is used. The reasons for not using direct transfers include improper alignment
of the user buffer (default is 512 bytes but this can be changed by the HBA
driver), one of more pages of the user buffer not reachable by the
SCSI adapter, etc.
.PP
A filemark is automatically written to tape if the last tape operation
before close was a write.
.PP
@ -191,8 +207,8 @@ The driver returns an EIO error if the drive rejects an operation.
.ta +.4i +.7i +1i
/* Structure for \s-1MTIOCTOP\s+1 \- mag tape op command: */
struct mtop {
short mt_op; /* operations defined below */
int mt_count; /* how many of them */
short mt_op; /* operations defined below */
int mt_count; /* how many of them */
};
.fi
.PP
@ -224,7 +240,8 @@ is zero. This command uses the MODE page 15 supported by most DATs.
.IP MTEOM
Go to the end of the recorded media (for appending files).
.IP MTERASE
Erase tape.
Erase tape. With 2.6 kernel, short erase (mark tape empty) is performed if the
argument is zero. Otherwise long erase (erase all) is done.
.IP MTFSF
Forward space over
.B mt_count
@ -290,7 +307,7 @@ The density codes supported by a drive can be found from the drive
documentation.
.IP MTSETPART
The active partition is switched to
.B mt_count .
.BR mt_count .
The partitions are numbered from zero. This command is not allowed for
a drive unless the partition support is enabled for the drive (see
MT_ST_CAN_PARTITIONS below).
@ -299,7 +316,7 @@ Execute the SCSI unload command (does not eject the tape).
.IP MTUNLOCK
Unlock the tape drive door.
.IP MTWEOF
Write
Write
.B mt_count
filemarks.
.IP MTWSM
@ -313,7 +330,7 @@ Magnetic Tape operations for setting of device options (by the superuser):
.IP MTSETDRVBUFFER 8
Set various drive and driver options according to bits encoded in
.BR mt_count .
These consist of the drive's buffering mode, 13 Boolean driver
These consist of the drive's buffering mode, a set of Boolean driver
options, the buffer write threshold, defaults for the block size and
density, and timeouts (only in kernels >= 2.1).
A single operation can affect only one item in the list above (the
@ -353,9 +370,9 @@ above).
To set and clear the Boolean options
the value in
.B mt_count
must include one the constants \s-1MT_ST_BOOLEANS\s+1,
must include one of the constants \s-1MT_ST_BOOLEANS\s+1,
\s-1MT_ST_SETBOOLEANS\s+1, \s-1MT_ST_CLEARBOOLEANS\s+1, or
\s-1MT_ST_DEFBOOLEANS\s+1 logically ORed with
\s-1MT_ST_DEFBOOLEANS\s+1 logically or'ed with
whatever combination of the following options is desired.
Using \s-1MT_ST_BOOLEANS\s+1 the options can be set to the values
defined in the corresponding bits. With \s-1MT_ST_SETBOOLEANS\s+1 the
@ -373,12 +390,12 @@ The Boolean options are:
.PD 0
.RS
.IP "\s-1MT_ST_BUFFER_WRITES\s+1 (Default: true)"
Buffer all write operations in fixed block mode.
Buffer all write operations in fixed-block mode.
If this option is false and the drive uses a fixed block size, then
all write operations must be for a multiple of the block size.
This option must be set false to write reliable multi-volume archives.
.IP "\s-1MT_ST_ASYNC_WRITES\s+1 (Default: true)"
When this options is true write operations return immediately without
When this option is true, write operations return immediately without
waiting for the data to be transferred to the drive if the data fits
into the driver's buffer.
The write threshold determines how full the buffer must be before a
@ -388,7 +405,7 @@ operation.
This option must be set false to write reliable multi-volume archives.
.IP "\s-1MT_ST_READ_AHEAD\s+1 (Default: true)"
This option causes the driver to provide read buffering and
read-ahead in fixed block mode.
read-ahead in fixed-block mode.
If this option is false and the drive uses a fixed block size, then
all read operations must be for a multiple of the block size.
.IP "\s-1MT_ST_TWO_FM\s+1 (Default: false)"
@ -439,8 +456,9 @@ correct position when the device is closed and the SCSI command to
space backwards over records is used for this purpose. Some older
drives can't process this command reliably and this option can be used
to instruct the driver not to use the command. The end result is that,
with read-ahead and fixed block mode, the tape may not be correctly
positioned within a file when the device is closed.
with read-ahead and fixed-block mode, the tape may not be correctly
positioned within a file when the device is closed. With 2.6 kernel, the
default is true for drives supporting SCSI-3.
.IP "\s-1MT_ST_NO_BLKLIMS\s+1 (Default: false)"
Some drives don't accept the READ BLOCK LIMITS SCSI command. If
this is used, the driver does not use the command. The drawback is
@ -464,14 +482,17 @@ difference between the semantics is what happens when a device used
for reading is closed: in SYSV semantics the tape is spaced forward
past the next filemark if this has not happened while using the
device. In BSD semantics the tape position is not changed.
.IP "\s-1MT_NO_WAIT\s+1 (Default: false)"
Enables immediate mode (i.e., don't wait for the command to finish) for some
commands (e.g., rewind).
.IP \s-1EXAMPLE\s+1
.nf
.ta +.4i +.7i +1i
.BI "struct mtop " mt_cmd ;
.IB "mt_cmd.mt_op" " = \s-1MTSETDRVBUFFER\s+1;"
.IB "mt_cmd.mt_count" " = \s-1MT_ST_BOOLEANS\s+1 |"
.B " \s-1MT_ST_BUFFER_WRITES\s+1 |"
.B " \s-1MT_ST_ASYNC_WRITES\s+1;"
.B " \s-1MT_ST_BUFFER_WRITES\s+1 |"
.B " \s-1MT_ST_ASYNC_WRITES\s+1;"
.BI "ioctl(" fd ", \s-1MTIOCTOP\s+1, &" mt_cmd ");"
.fi
.RE
@ -479,11 +500,11 @@ device. In BSD semantics the tape position is not changed.
.IP ""
The default block size for a device can be set with
\s-1MT_ST_DEF_BLKSIZE\s+1 and the default density code can be set with
\s-1MT_ST_DEFDENSITY\s+1. The values for the parameters are ORed
\s-1MT_ST_DEFDENSITY\s+1. The values for the parameters are or'ed
with the operation code.
.IP ""
With kernels 2.1.x and later, the timeout values can be set with the
subcommand \s-1MT_ST_SET_TIMEOUT\s+1 or'ed with the timeout in seconds.
subcommand \s-1MT_ST_SET_TIMEOUT\s+1 ORed with the timeout in seconds.
The long timeout (used for rewinds and other commands
that may take a long time) can be set with
\s-1MT_ST_SET_LONG_TIMEOUT\s+1. The kernel defaults are very long to
@ -492,6 +513,20 @@ drive. Because of this the driver may seem stuck even if it is only
waiting for the timeout. These commands can be used to set more
practical values for a specific drive. The timeouts set for one device
apply for all devices linked to the same drive.
.IP ""
Starting from kernels 2.4.19 and 2.5.43, the driver supports a status
bit which indicates whether the drive requests cleaning.
The method used by the
drive to return cleaning information is set using the
\s-1MT_ST_SEL_CLN\s+1 subcommand. If the value is zero, the cleaning
bit is always zero. If the value is one, the TapeAlert data defined
in the SCSI-3 standard is used (not yet implemented). Values 2-17 are
reserved. If the lowest eight bits are >= 18, bits from the extended
sense data are used. The bits 9-16 specify a mask to select the bits
to look at and the bits 17-23 specify the bit pattern to look for.
If the bit pattern is zero, one or more bits under the mask indicate
the cleaning request. If the pattern is non-zero, the pattern must match
the masked sense data byte.
.SS "\s-1MTIOCGET\s+1 \- Get status"
.PP
This request takes an argument of type
@ -500,15 +535,15 @@ This request takes an argument of type
.nf
/* structure for \s-1MTIOCGET\s+1 - mag tape get status command */
struct mtget {
long mt_type;
long mt_resid;
/* the following registers are device dependent */
long mt_dsreg;
long mt_gstat;
long mt_erreg;
/* The next two fields are not always used */
daddr_t mt_fileno;
daddr_t mt_blkno;
long mt_type;
long mt_resid;
/* the following registers are device dependent */
long mt_dsreg;
long mt_gstat;
long mt_erreg;
/* The next two fields are not always used */
daddr_t mt_fileno;
daddr_t mt_blkno;
};
.fi
.IP \fBmt_type\fP 11
@ -569,6 +604,9 @@ Immediate report mode. This bit is set if there are no guarantees that
the data has been physically written to the tape when the write call
returns. It is set zero only when the driver does not buffer data and
the drive is set not to buffer data.
.HP
\s-1GMT_CLN(\s+1\fIx\fP\s-1)\s+1:
The drive has requested cleaning. Implemented in kernels >= 2.4.19 and 2.5.43.
.RE
.IP \fBmt_erreg\fP
The only field defined in
@ -604,8 +642,8 @@ Viper, Wangtek, ... ).
.PP
.nf
/* structure for \s-1MTIOCPOS\s+1 - mag tape get position command */
struct mtpos {
long mt_blkno; /* current block number */
struct mtpos {
long mt_blkno; /* current block number */
};
.fi
@ -615,6 +653,10 @@ The requested operation could not be completed.
.IP ENOSPC
A write operation could not be completed because the tape reached
end-of-medium.
.IP ENOMEM
The byte count in read() is smaller than the next physical block on
the tape. (Before 2.2.18 and 2.4.0-test6 the extra bytes have been
silently ignored.)
.IP EACCES
An attempt was made to write or erase a write-protected tape.
(This error is not detected during
@ -651,25 +693,25 @@ people have also contributed to the driver.
.SH "SEE ALSO"
.BR mt (1)
.PP
The file README.st in the kernel sources contains the most recent
information about the driver and its configuration
The file README.st or st.txt (kernel >= 2.6) in the kernel sources contains
the most recent information about the driver and its configuration
possibilities.
.SH NOTES
1. When exchanging data between systems, both systems have to agree on
the physical tape block size. The parameters of a drive after startup
are often not the ones most operating systems use with these
devices. Most systems use drives in variable block mode if the drive
devices. Most systems use drives in variable-block mode if the drive
supports that mode. This applies to most modern drives, including
DATs, 8mm helical scan drives, DLTs, etc. It may be advisable use
these drives in variable block mode also in Linux (i.e., use MTSETBLK
DATs, 8mm helical scan drives, DLTs, etc. It may be advisable to use
these drives in variable-block mode also in Linux (i.e., use MTSETBLK
or MTSETDEFBLK at system startup to set the mode), at least when
exchanging data with foreign system. The drawback of
exchanging data with a foreign system. The drawback of
this is that a fairly large tape block size has to be used to get
acceptable data transfer rates on the SCSI bus.
.PP
2. Many programs (e.g., tar) allow the user to specify the blocking
factor on command line. Note that this determines the physical block
size on tape only in variable block mode.
factor on the command line. Note that this determines the physical block
size on tape only in variable-block mode.
.PP
3. In order to use SCSI tape drives, the basic SCSI driver,
a SCSI-adapter driver and the SCSI tape driver must be either
@ -680,10 +722,18 @@ described in this page is not available.
4. The driver writes error messages to the console/log. The SENSE
codes written into some messages are automatically translated to text
if verbose SCSI messages are enabled in kernel configuration.
.PP
5. The driver's internal buffering allows good throughput in fixed-block
mode also with small read() and write() byte counts. With direct transfers
this is not possible and may cause a surprise when moving to the 2.6
kernel.
The solution is to tell the software to use larger transfers (often
telling it to use larger blocks).
If this is not possible, direct transfers can be disabled.
.SH COPYRIGHT
Copyright \(co 1995 Robert K. Nichols.
.br
Copyright \(co 1999 Kai M\(:akisara.
Copyright \(co 1999-2005 Kai M\(:akisara.
.PP
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are