diff options
Diffstat (limited to 'man/man4/st.4')
| -rw-r--r-- | man/man4/st.4 | 950 |
1 files changed, 950 insertions, 0 deletions
diff --git a/man/man4/st.4 b/man/man4/st.4 new file mode 100644 index 000000000..3dd16d744 --- /dev/null +++ b/man/man4/st.4 @@ -0,0 +1,950 @@ +.\" Copyright 1995 Robert K. Nichols (Robert.K.Nichols@att.com) +.\" Copyright 1999-2005 Kai Mäkisara (Kai.Makisara@kolumbus.fi) +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.TH st 4 (date) "Linux man-pages (unreleased)" +.SH NAME +st \- SCSI tape device +.SH SYNOPSIS +.nf +.B #include <sys/mtio.h> +.P +.BI "int ioctl(int " fd ", int " request " [, (void *)" arg3 "]);" +.BI "int ioctl(int " fd ", MTIOCTOP, (struct mtop *)" mt_cmd ); +.BI "int ioctl(int " fd ", MTIOCGET, (struct mtget *)" mt_status ); +.BI "int ioctl(int " fd ", MTIOCPOS, (struct mtpos *)" mt_pos ); +.fi +.SH DESCRIPTION +The +.B st +driver provides the interface to a variety of SCSI tape devices. +Currently, the driver takes control of all detected devices of type +\[lq]sequential-access\[rq]. +The +.B st +driver uses major device number 9. +.P +Each device uses eight minor device numbers. +The lowermost five bits +in the minor numbers are assigned sequentially in the order of +detection. +In the 2.6 kernel, the bits above the eight lowermost bits are +concatenated to the five lowermost 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 the \[lq]no-rewind\[rq] device numbers, +.RI ( n " + 128)." +Devices opened using the principal device number will be sent a +.B REWIND +command when they are closed. +Devices opened using the \[lq]no-rewind\[rq] device number will not. +(Note that using an auto-rewind device for positioning the tape with, +for instance, mt does not lead to the desired result: the tape is +rewound after the mt command and the next command starts from the +beginning of the tape). +.P +Within each group, four minor numbers are available to define +devices with different characteristics (block size, compression, +density, etc.) +When the system starts up, only the first device is available. +The other three are activated when the default +characteristics are defined (see below). +(By changing compile-time +constants, it is possible to change the balance between the maximum +number of tape drives and the number of minor numbers for each +drive. +The default allocation allows control of 32 tape drives. +For instance, it is possible to control up to 64 tape drives +with two minor numbers for different options.) +.P +Devices are typically created by: +.P +.in +4n +.EX +mknod \-m 666 /dev/st0 c 9 0 +mknod \-m 666 /dev/st0l c 9 32 +mknod \-m 666 /dev/st0m c 9 64 +mknod \-m 666 /dev/st0a c 9 96 +mknod \-m 666 /dev/nst0 c 9 128 +mknod \-m 666 /dev/nst0l c 9 160 +mknod \-m 666 /dev/nst0m c 9 192 +mknod \-m 666 /dev/nst0a c 9 224 +.EE +.in +.P +There is no corresponding block device. +.P +The driver uses an internal buffer that has to be large enough to hold +at least one tape block. +Before Linux 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 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). +.P +The driver's internal buffer size is determined by a compile-time +constant which can be overridden with a kernel startup option. +In addition to this, the driver tries to allocate a larger temporary +buffer at run time if necessary. +However, run-time allocation of large +contiguous blocks of memory may fail and it is advisable not to rely +too much on dynamic buffer allocation before Linux 2.1.121 +(this applies also to demand-loading the driver with kerneld or kmod). +.P +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 +be changed with explicit +.BR ioctl (2) +calls and remain in effect when the device is closed and reopened. +Setting the options affects both the auto-rewind and the nonrewind +device. +.P +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 +both modes). +.P +The driver supports +.B tape partitions +if they are supported by the drive. +(Note that the tape partitions +have nothing to do with disk partitions. +A partitioned tape can be +seen as several logical tapes within one medium.) +Partition support has to be enabled with an +.BR ioctl (2). +The tape +location is preserved within each partition across partition changes. +The partition used for subsequent tape operations is +selected with an +.BR ioctl (2). +The partition switch is executed together with +the next tape operation in order to avoid unnecessary tape +movement. +The maximum number of partitions on a tape is defined by a +compile-time constant (originally four). +The driver contains an +.BR ioctl (2) +that can format a tape with either one or two partitions. +.P +Device +.I /dev/tape +is usually created as a hard or soft link to the default tape device +on the system. +.P +Starting from Linux 2.6.2, the driver exports in the sysfs directory +.I /sys/class/scsi_tape +the attached devices and some parameters assigned to the devices. +.SS 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 +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 +count determines the size of the corresponding tape block. +Note that +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. +.P +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, an error is returned. +.P +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. +Before Linux 2.1.121 allow writes with +arbitrary byte count if buffering is enabled. +In all other cases +(before Linux 2.1.121 with buffering disabled or newer kernel) the +write byte count must be a multiple of the tape block size. +.P +In Linux 2.6, 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 or more pages of the user buffer not reachable by the +SCSI adapter, and so on. +.P +A filemark is automatically written to tape if the last tape operation +before close was a write. +.P +When a filemark is encountered while reading, the following +happens. +If there are data remaining in the buffer when the filemark +is found, the buffered data is returned. +The next read returns zero +bytes. +The following read returns data from the next file. +The end of +recorded data is signaled by returning zero bytes for two consecutive +read calls. +The third read returns an error. +.SS Ioctls +The driver supports three +.BR ioctl (2) +requests. +Requests not recognized by the +.B st +driver are passed to the +.B SCSI +driver. +The definitions below are from +.IR /usr/include/linux/mtio.h : +.SS MTIOCTOP \[em] perform a tape operation +This request takes an argument of type +.IR "(struct mtop\ *)" . +Not all drives support all operations. +The driver returns an +.B EIO +error if the drive rejects an operation. +.P +.in +4n +.EX +/* Structure for MTIOCTOP \- mag tape op command: */ +struct mtop { + short mt_op; /* operations defined below */ + int mt_count; /* how many of them */ +}; +.EE +.in +.P +Magnetic tape operations for normal tape use: +.TP +.B MTBSF +Backward space over +.I mt_count +filemarks. +.TP +.B MTBSFM +Backward space over +.I mt_count +filemarks. +Reposition the tape to the EOT side of the last filemark. +.TP +.B MTBSR +Backward space over +.I mt_count +records (tape blocks). +.TP +.B MTBSS +Backward space over +.I mt_count +setmarks. +.TP +.B MTCOMPRESSION +Enable compression of tape data within the drive if +.I mt_count +is nonzero and disable compression if +.I mt_count +is zero. +This command uses the MODE page 15 supported by most DATs. +.TP +.B MTEOM +Go to the end of the recorded media (for appending files). +.TP +.B MTERASE +Erase tape. +With Linux 2.6, short erase (mark tape empty) is performed if the +argument is zero. +Otherwise, long erase (erase all) is done. +.TP +.B MTFSF +Forward space over +.I mt_count +filemarks. +.TP +.B MTFSFM +Forward space over +.I mt_count +filemarks. +Reposition the tape to the BOT side of the last filemark. +.TP +.B MTFSR +Forward space over +.I mt_count +records (tape blocks). +.TP +.B MTFSS +Forward space over +.I mt_count +setmarks. +.TP +.B MTLOAD +Execute the SCSI load command. +A special case is available for some HP +autoloaders. +If +.I mt_count +is the constant +.B MT_ST_HPLOADER_OFFSET +plus a number, the number is +sent to the drive to control the autoloader. +.TP +.B MTLOCK +Lock the tape drive door. +.TP +.B MTMKPART +Format the tape into one or two partitions. +If +.I mt_count +is positive, it gives the size of partition 1 and partition +0 contains the rest of the tape. +If +.I mt_count +is zero, the tape is formatted into one partition. +From Linux 4.6, +.\" commit 8038e6456a3e6f5c4759e0d73c4f9165b90c93e7 +a negative +.I mt_count +specifies the size of partition 0 and +the rest of the tape contains partition 1. +The physical ordering of partitions depends on the drive. +This command is not allowed for a drive unless the partition support +is enabled for the drive (see +.B MT_ST_CAN_PARTITIONS +below). +.TP +.B MTNOP +No op\[em]flushes the driver's buffer as a side effect. +Should be used before reading status with +.BR MTIOCGET . +.TP +.B MTOFFL +Rewind and put the drive off line. +.TP +.B MTRESET +Reset drive. +.TP +.B MTRETEN +Re-tension tape. +.TP +.B MTREW +Rewind. +.TP +.B MTSEEK +Seek to the tape block number specified in +.IR mt_count . +This operation requires either a SCSI-2 drive that supports the +.B LOCATE +command (device-specific address) +or a Tandberg-compatible SCSI-1 drive (Tandberg, Archive +Viper, Wangtek, ...). +The block number should be one that was previously returned by +.B MTIOCPOS +if device-specific addresses are used. +.TP +.B MTSETBLK +Set the drive's block length to the value specified in +.IR mt_count . +A block length of zero sets the drive to variable block size mode. +.TP +.B MTSETDENSITY +Set the tape density to the code in +.IR mt_count . +The density codes supported by a drive can be found from the drive +documentation. +.TP +.B MTSETPART +The active partition is switched to +.IR 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 +.B MT_ST_CAN_PARTITIONS +below). +.TP +.B MTUNLOAD +Execute the SCSI unload command (does not eject the tape). +.TP +.B MTUNLOCK +Unlock the tape drive door. +.TP +.B MTWEOF +Write +.I mt_count +filemarks. +.TP +.B MTWSM +Write +.I mt_count +setmarks. +.P +Magnetic tape operations for setting of device options (by the superuser): +.TP +.B MTSETDRVBUFFER +Set various drive and driver options according to bits encoded in +.IR mt_count . +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 since Linux 2.1). +A single operation can affect only one item in the list below (the +Booleans counted as one item.) +.IP +A value having zeros in the high-order 4 bits will be used to set the +drive's buffering mode. +The buffering modes are: +.RS +.TP +.B 0 +The drive will not report +.B GOOD +status on write commands until the data +blocks are actually written to the medium. +.TP +.B 1 +The drive may report +.B GOOD +status on write commands as soon as all the +data has been transferred to the drive's internal buffer. +.TP +.B 2 +The drive may report +.B GOOD +status on write commands as soon as (a) all +the data has been transferred to the drive's internal buffer, and +(b) all buffered data from different initiators has been successfully +written to the medium. +.RE +.IP +To control the write threshold the value in +.I mt_count +must include the constant +.B MT_ST_WRITE_THRESHOLD +bitwise ORed with a block count in the low 28 bits. +The block count refers to 1024-byte blocks, not the physical block +size on the tape. +The threshold cannot exceed the driver's internal buffer size (see +DESCRIPTION, above). +.IP +To set and clear the Boolean options +the value in +.I mt_count +must include one of the constants +.BR MT_ST_BOOLEANS , +.BR MT_ST_SETBOOLEANS , +.BR MT_ST_CLEARBOOLEANS , +or +.B MT_ST_DEFBOOLEANS +bitwise ORed with +whatever combination of the following options is desired. +Using +.B MT_ST_BOOLEANS +the options can be set to the values +defined in the corresponding bits. +With +.B MT_ST_SETBOOLEANS +the options can be selectively set and with +.B MT_ST_DEFBOOLEANS +selectively cleared. +.IP +The default options for a tape device are set with +.BR MT_ST_DEFBOOLEANS . +A nonactive tape device (e.g., device with +minor 32 or 160) is activated when the default options for it are +defined the first time. +An activated device inherits from the device +activated at start-up the options not set explicitly. +.IP +The Boolean options are: +.RS +.TP +.BR MT_ST_BUFFER_WRITES " (Default: true)" +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 multivolume archives. +.TP +.BR MT_ST_ASYNC_WRITES " (Default: true)" +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 +new SCSI write command is issued. +Any errors reported by the drive will be held until the next +operation. +This option must be set false to write reliable multivolume archives. +.TP +.BR MT_ST_READ_AHEAD " (Default: true)" +This option causes the driver to provide read buffering and +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. +.TP +.BR MT_ST_TWO_FM " (Default: false)" +This option modifies the driver behavior when a file is closed. +The normal action is to write a single filemark. +If the option is true, the driver will write two filemarks and +backspace over the second one. +.IP +Note: +This option should not be set true for QIC tape drives since they are +unable to overwrite a filemark. +These drives detect the end of recorded data by testing for blank tape +rather than two consecutive filemarks. +Most other current drives also +detect the end of recorded data and using two filemarks is usually +necessary only when interchanging tapes with some other systems. +.TP +.BR MT_ST_DEBUGGING " (Default: false)" +This option turns on various debugging messages from the driver +(effective only if the driver was compiled with +.B DEBUG +defined nonzero). +.TP +.BR MT_ST_FAST_EOM " (Default: false)" +This option causes the +.B MTEOM +operation to be sent directly to the +drive, potentially speeding up the operation but causing the driver to +lose track of the current file number normally returned by the +.B MTIOCGET +request. +If +.B MT_ST_FAST_EOM +is false, the driver will respond to an +.B MTEOM +request by forward spacing over files. +.TP +.BR MT_ST_AUTO_LOCK " (Default: false)" +When this option is true, the drive door is locked when the device file is +opened and unlocked when it is closed. +.TP +.BR MT_ST_DEF_WRITES " (Default: false)" +The tape options (block size, mode, compression, etc.) may change +when changing from one device linked to a drive to another device +linked to the same drive depending on how the devices are +defined. +This option defines when the changes are enforced by the +driver using SCSI-commands and when the drives auto-detection +capabilities are relied upon. +If this option is false, the driver +sends the SCSI-commands immediately when the device is changed. +If the +option is true, the SCSI-commands are not sent until a write is +requested. +In this case, the drive firmware is allowed to detect the +tape structure when reading and the SCSI-commands are used only to +make sure that a tape is written according to the correct specification. +.TP +.BR MT_ST_CAN_BSR " (Default: false)" +When read-ahead is used, the tape must sometimes be spaced backward to the +correct position when the device is closed and the SCSI command to +space backward 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 Linux 2.6, the +default is true for drives supporting SCSI-3. +.TP +.BR MT_ST_NO_BLKLIMS " (Default: false)" +Some drives don't accept the +.B "READ BLOCK LIMITS" +SCSI command. +If this is used, the driver does not use the command. +The drawback is +that the driver can't check before sending commands if the selected +block size is acceptable to the drive. +.TP +.BR MT_ST_CAN_PARTITIONS " (Default: false)" +This option enables support for several partitions within a +tape. +The option applies to all devices linked to a drive. +.TP +.BR MT_ST_SCSI2LOGICAL " (Default: false)" +This option instructs the driver to use the logical block addresses +defined in the SCSI-2 standard when performing the seek and tell +operations (both with +.B MTSEEK +and +.B MTIOCPOS +commands and when changing tape +partition). +Otherwise, the device-specific addresses are used. +It is highly advisable to set this option if the drive supports the +logical addresses because they count also filemarks. +There are some +drives that support only the logical block addresses. +.TP +.BR MT_ST_SYSV " (Default: false)" +When this option is enabled, the tape devices use the System V +semantics. +Otherwise, the BSD semantics are used. +The most important +difference between the semantics is what happens when a device used +for reading is closed: in System V 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. +.TP +.BR MT_NO_WAIT " (Default: false)" +Enables immediate mode (i.e., don't wait for the command to finish) for some +commands (e.g., rewind). +.P +An example: +.P +.in +4n +.EX +struct mtop mt_cmd; +mt_cmd.mt_op = MTSETDRVBUFFER; +mt_cmd.mt_count = MT_ST_BOOLEANS | + MT_ST_BUFFER_WRITES | MT_ST_ASYNC_WRITES; +ioctl(fd, MTIOCTOP, mt_cmd); +.EE +.in +.P +The default block size for a device can be set with +.B MT_ST_DEF_BLKSIZE +and the default density code can be set with +.BR MT_ST_DEFDENSITY . +The values for the parameters are or'ed +with the operation code. +.P +With Linux 2.1.x and later, the timeout values can be set with the +subcommand +.B MT_ST_SET_TIMEOUT +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 +.BR MT_ST_SET_LONG_TIMEOUT . +The kernel defaults are very long to +make sure that a successful command is not timed out with any +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. +.P +Starting from Linux 2.4.19 and Linux 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 +.B MT_ST_SEL_CLN +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\[en]17 are +reserved. +If the lowest eight bits are >= 18, bits from the extended +sense data are used. +The bits 9\[en]16 specify a mask to select the bits +to look at and the bits 17\[en]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 nonzero, the pattern must match +the masked sense data byte. +.RE +.SS MTIOCGET \[em] get status +This request takes an argument of type +.IR "(struct mtget\ *)" . +.P +.in +4n +.EX +/* structure for MTIOCGET \- 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; +}; +.EE +.in +.TP +\fImt_type\fP +The header file defines many values for +.IR mt_type , +but the current driver reports only the generic types +.B MT_ISSCSI1 +(Generic SCSI-1 tape) +and +.B MT_ISSCSI2 +(Generic SCSI-2 tape). +.TP +\fImt_resid\fP +contains the current tape partition number. +.TP +\fImt_dsreg\fP +reports the drive's current settings for block size (in the low 24 +bits) and density (in the high 8 bits). +These fields are defined by +.BR MT_ST_BLKSIZE_SHIFT , +.BR MT_ST_BLKSIZE_MASK , +.BR MT_ST_DENSITY_SHIFT , +and +.BR MT_ST_DENSITY_MASK . +.TP +\fImt_gstat\fP +reports generic (device independent) status information. +The header file defines macros for testing these status bits: +.RS +.TP +\fBGMT_EOF\fP(\fIx\fP) +The tape is positioned just after a filemark +(always false after an +.B MTSEEK +operation). +.TP +\fBGMT_BOT\fP(\fIx\fP) +The tape is positioned at the beginning of the first file (always false +after an +.B MTSEEK +operation). +.TP +\fBGMT_EOT\fP(\fIx\fP) +A tape operation has reached the physical End Of Tape. +.TP +\fBGMT_SM\fP(\fIx\fP) +The tape is currently positioned at a setmark +(always false after an +.B MTSEEK +operation). +.TP +\fBGMT_EOD\fP(\fIx\fP) +The tape is positioned at the end of recorded data. +.TP +\fBGMT_WR_PROT\fP(\fIx\fP) +The drive is write-protected. +For some drives this can also mean that the drive does not support +writing on the current medium type. +.TP +\fBGMT_ONLINE\fP(\fIx\fP) +The last +.BR open (2) +found the drive with a tape in place and ready for operation. +.TP +\fBGMT_D_6250\fP(\fIx\fP) +.TQ +\fBGMT_D_1600\fP(\fIx\fP) +.TQ +\fBGMT_D_800\fP(\fIx\fP) +This \[lq]generic\[rq] status information reports the current +density setting for 9-track \(12" tape drives only. +.TP +\fBGMT_DR_OPEN\fP(\fIx\fP) +The drive does not have a tape in place. +.TP +\fBGMT_IM_REP_EN\fP(\fIx\fP) +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. +.TP +\fBGMT_CLN\fP(\fIx\fP) +The drive has requested cleaning. +Implemented since Linux 2.4.19 and Linux 2.5.43. +.RE +.TP +\fImt_erreg\fP +The only field defined in +.I mt_erreg +is the recovered error count in the low 16 bits (as defined by +.B MT_ST_SOFTERR_SHIFT +and +.BR MT_ST_SOFTERR_MASK ). +Due to inconsistencies in the way drives report recovered errors, this +count is often not maintained (most drives do not by default report +soft errors but this can be changed with a SCSI MODE SELECT command). +.TP +\fImt_fileno\fP +reports the current file number (zero-based). +This value is set to \-1 when the file number is unknown (e.g., after +.B MTBSS +or +.BR MTSEEK ). +.TP +\fImt_blkno\fP +reports the block number (zero-based) within the current file. +This value is set to \-1 when the block number is unknown (e.g., after +.BR MTBSF , +.BR MTBSS , +or +.BR MTSEEK ). +.SS MTIOCPOS \[em] get tape position +This request takes an argument of type +.I "(struct mtpos\ *)" +and reports the drive's notion of the current tape block number, +which is not the same as +.I mt_blkno +returned by +.BR MTIOCGET . +This drive must be a SCSI-2 drive that supports the +.B "READ POSITION" +command (device-specific address) +or a Tandberg-compatible SCSI-1 drive (Tandberg, Archive +Viper, Wangtek, ... ). +.P +.in +4n +.EX +/* structure for MTIOCPOS \- mag tape get position command */ +struct mtpos { + long mt_blkno; /* current block number */ +}; +.EE +.in +.SH RETURN VALUE +.TP +.B EACCES +An attempt was made to write or erase a write-protected tape. +(This error is not detected during +.BR open (2).) +.TP +.B EBUSY +The device is already in use or the driver was unable to allocate a +buffer. +.TP +.B EFAULT +The command parameters point to memory not belonging to the calling +process. +.TP +.B EINVAL +An +.BR ioctl (2) +had an invalid argument, or a requested block size was invalid. +.TP +.B EIO +The requested operation could not be completed. +.TP +.B ENOMEM +The byte count in +.BR read (2) +is smaller than the next physical block on the tape. +(Before Linux 2.2.18 and Linux 2.4.0 the extra bytes have been +.\" Precisely: Linux 2.6.0-test6 +silently ignored.) +.TP +.B ENOSPC +A write operation could not be completed because the tape reached +end-of-medium. +.TP +.B ENOSYS +Unknown +.BR ioctl (2). +.TP +.B ENXIO +During opening, the tape device does not exist. +.TP +.B EOVERFLOW +An attempt was made to read or write a variable-length block that is +larger than the driver's internal buffer. +.TP +.B EROFS +Open is attempted with +.B O_WRONLY +or +.B O_RDWR +when the tape in the drive is write-protected. +.SH FILES +.TP +.I /dev/st* +the auto-rewind SCSI tape devices +.TP +.I /dev/nst* +the nonrewind SCSI tape devices +.\" .SH AUTHOR +.\" The driver has been written by Kai M\(:akisara (Kai.Makisara@metla.fi) +.\" starting from a driver written by Dwayne Forsyth. +.\" Several other +.\" people have also contributed to the driver. +.SH NOTES +.IP \[bu] 3 +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 +supports that mode. +This applies to most modern drives, including +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 +.B MTSETBLK +or +.B MTSETDEFBLK +at system startup to set the mode), at least when +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. +.IP \[bu] +Many programs (e.g., +.BR tar (1)) +allow the user to specify the blocking +factor on the command line. +Note that this determines the physical block +size on tape only in variable-block mode. +.IP \[bu] +In order to use SCSI tape drives, the basic SCSI driver, +a SCSI-adapter driver and the SCSI tape driver must be either +configured into the kernel or loaded as modules. +If the SCSI-tape +driver is not present, the drive is recognized but the tape support +described in this page is not available. +.IP \[bu] +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. +.IP \[bu] +The driver's internal buffering allows good throughput in fixed-block +mode also with small +.BR read (2) +and +.BR write (2) +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 SEE ALSO +.BR mt (1) +.P +The file +.I drivers/scsi/README.st +or +.I Documentation/scsi/st.txt +(kernel >= 2.6) in the Linux kernel source tree contains +the most recent information about the driver and its configuration +possibilities |