scsi
sd-parameters
smartpqi
+ st
scsi_transport_srp/figures
osst= [HW,SCSI] SCSI Tape Driver
Format: <buffer_size>,<write_threshold>
- See also Documentation/scsi/st.txt.
+ See also Documentation/scsi/st.rst.
scsi_debug_*= [SCSI]
See drivers/scsi/scsi_debug.c.
See header of drivers/scsi/sim710.c.
st= [HW,SCSI] SCSI tape parameters (buffers, etc.)
- See Documentation/scsi/st.txt.
+ See Documentation/scsi/st.rst.
wd33c93= [HW,SCSI]
See header of drivers/scsi/wd33c93.c.
--- /dev/null
+.. SPDX-License-Identifier: GPL-2.0
+
+====================
+The SCSI Tape Driver
+====================
+
+This file contains brief information about the SCSI tape driver.
+The driver is currently maintained by Kai Mäkisara (email
+Kai.Makisara@kolumbus.fi)
+
+Last modified: Tue Feb 9 21:54:16 2016 by kai.makisara
+
+
+Basics
+======
+
+The driver is generic, i.e., it does not contain any code tailored
+to any specific tape drive. The tape parameters can be specified with
+one of the following three methods:
+
+1. Each user can specify the tape parameters he/she wants to use
+directly with ioctls. This is administratively a very simple and
+flexible method and applicable to single-user workstations. However,
+in a multiuser environment the next user finds the tape parameters in
+state the previous user left them.
+
+2. The system manager (root) can define default values for some tape
+parameters, like block size and density using the MTSETDRVBUFFER ioctl.
+These parameters can be programmed to come into effect either when a
+new tape is loaded into the drive or if writing begins at the
+beginning of the tape. The second method is applicable if the tape
+drive performs auto-detection of the tape format well (like some
+QIC-drives). The result is that any tape can be read, writing can be
+continued using existing format, and the default format is used if
+the tape is rewritten from the beginning (or a new tape is written
+for the first time). The first method is applicable if the drive
+does not perform auto-detection well enough and there is a single
+"sensible" mode for the device. An example is a DAT drive that is
+used only in variable block mode (I don't know if this is sensible
+or not :-).
+
+The user can override the parameters defined by the system
+manager. The changes persist until the defaults again come into
+effect.
+
+3. By default, up to four modes can be defined and selected using the minor
+number (bits 5 and 6). The number of modes can be changed by changing
+ST_NBR_MODE_BITS in st.h. Mode 0 corresponds to the defaults discussed
+above. Additional modes are dormant until they are defined by the
+system manager (root). When specification of a new mode is started,
+the configuration of mode 0 is used to provide a starting point for
+definition of the new mode.
+
+Using the modes allows the system manager to give the users choices
+over some of the buffering parameters not directly accessible to the
+users (buffered and asynchronous writes). The modes also allow choices
+between formats in multi-tape operations (the explicitly overridden
+parameters are reset when a new tape is loaded).
+
+If more than one mode is used, all modes should contain definitions
+for the same set of parameters.
+
+Many Unices contain internal tables that associate different modes to
+supported devices. The Linux SCSI tape driver does not contain such
+tables (and will not do that in future). Instead of that, a utility
+program can be made that fetches the inquiry data sent by the device,
+scans its database, and sets up the modes using the ioctls. Another
+alternative is to make a small script that uses mt to set the defaults
+tailored to the system.
+
+The driver supports fixed and variable block size (within buffer
+limits). Both the auto-rewind (minor equals device number) and
+non-rewind devices (minor is 128 + device number) are implemented.
+
+In variable block mode, the byte count in write() determines the size
+of the physical block on tape. When reading, the drive reads the next
+tape block and returns to the user the data if the read() byte count
+is at least the block size. Otherwise, error ENOMEM is returned.
+
+In fixed block mode, the data transfer between the drive and the
+driver is in multiples of the block size. The write() byte count must
+be a multiple of the block size. This is not required when reading but
+may be advisable for portability.
+
+Support is provided for changing the tape partition and partitioning
+of the tape with one or two partitions. By default support for
+partitioned tape is disabled for each driver and it can be enabled
+with the ioctl MTSETDRVBUFFER.
+
+By default the driver writes one filemark when the device is closed after
+writing and the last operation has been a write. Two filemarks can be
+optionally written. In both cases end of data is signified by
+returning zero bytes for two consecutive reads.
+
+Writing filemarks without the immediate bit set in the SCSI command block acts
+as a synchronization point, i.e., all remaining data form the drive buffers is
+written to tape before the command returns. This makes sure that write errors
+are caught at that point, but this takes time. In some applications, several
+consecutive files must be written fast. The MTWEOFI operation can be used to
+write the filemarks without flushing the drive buffer. Writing filemark at
+close() is always flushing the drive buffers. However, if the previous
+operation is MTWEOFI, close() does not write a filemark. This can be used if
+the program wants to close/open the tape device between files and wants to
+skip waiting.
+
+If rewind, offline, bsf, or seek is done and previous tape operation was
+write, a filemark is written before moving tape.
+
+The compile options are defined in the file linux/drivers/scsi/st_options.h.
+
+4. If the open option O_NONBLOCK is used, open succeeds even if the
+drive is not ready. If O_NONBLOCK is not used, the driver waits for
+the drive to become ready. If this does not happen in ST_BLOCK_SECONDS
+seconds, open fails with the errno value EIO. With O_NONBLOCK the
+device can be opened for writing even if there is a write protected
+tape in the drive (commands trying to write something return error if
+attempted).
+
+
+Minor Numbers
+=============
+
+The tape driver currently supports up to 2^17 drives if 4 modes for
+each drive are used.
+
+The minor numbers consist of the following bit fields::
+
+ dev_upper non-rew mode dev-lower
+ 20 - 8 7 6 5 4 0
+
+The non-rewind bit is always bit 7 (the uppermost bit in the lowermost
+byte). The bits defining the mode are below the non-rewind bit. The
+remaining bits define the tape device number. This numbering is
+backward compatible with the numbering used when the minor number was
+only 8 bits wide.
+
+
+Sysfs Support
+=============
+
+The driver creates the directory /sys/class/scsi_tape and populates it with
+directories corresponding to the existing tape devices. There are autorewind
+and non-rewind entries for each mode. The names are stxy and nstxy, where x
+is the tape number and y a character corresponding to the mode (none, l, m,
+a). For example, the directories for the first tape device are (assuming four
+modes): st0 nst0 st0l nst0l st0m nst0m st0a nst0a.
+
+Each directory contains the entries: default_blksize default_compression
+default_density defined dev device driver. The file 'defined' contains 1
+if the mode is defined and zero if not defined. The files 'default_*' contain
+the defaults set by the user. The value -1 means the default is not set. The
+file 'dev' contains the device numbers corresponding to this device. The links
+'device' and 'driver' point to the SCSI device and driver entries.
+
+Each directory also contains the entry 'options' which shows the currently
+enabled driver and mode options. The value in the file is a bit mask where the
+bit definitions are the same as those used with MTSETDRVBUFFER in setting the
+options.
+
+A link named 'tape' is made from the SCSI device directory to the class
+directory corresponding to the mode 0 auto-rewind device (e.g., st0).
+
+
+Sysfs and Statistics for Tape Devices
+=====================================
+
+The st driver maintains statistics for tape drives inside the sysfs filesystem.
+The following method can be used to locate the statistics that are
+available (assuming that sysfs is mounted at /sys):
+
+1. Use opendir(3) on the directory /sys/class/scsi_tape
+2. Use readdir(3) to read the directory contents
+3. Use regcomp(3)/regexec(3) to match directory entries to the extended
+ regular expression "^st[0-9]+$"
+4. Access the statistics from the /sys/class/scsi_tape/<match>/stats
+ directory (where <match> is a directory entry from /sys/class/scsi_tape
+ that matched the extended regular expression)
+
+The reason for using this approach is that all the character devices
+pointing to the same tape drive use the same statistics. That means
+that st0 would have the same statistics as nst0.
+
+The directory contains the following statistics files:
+
+1. in_flight
+ - The number of I/Os currently outstanding to this device.
+2. io_ns
+ - The amount of time spent waiting (in nanoseconds) for all I/O
+ to complete (including read and write). This includes tape movement
+ commands such as seeking between file or set marks and implicit tape
+ movement such as when rewind on close tape devices are used.
+3. other_cnt
+ - The number of I/Os issued to the tape drive other than read or
+ write commands. The time taken to complete these commands uses the
+ following calculation io_ms-read_ms-write_ms.
+4. read_byte_cnt
+ - The number of bytes read from the tape drive.
+5. read_cnt
+ - The number of read requests issued to the tape drive.
+6. read_ns
+ - The amount of time (in nanoseconds) spent waiting for read
+ requests to complete.
+7. write_byte_cnt
+ - The number of bytes written to the tape drive.
+8. write_cnt
+ - The number of write requests issued to the tape drive.
+9. write_ns
+ - The amount of time (in nanoseconds) spent waiting for write
+ requests to complete.
+10. resid_cnt
+ - The number of times during a read or write we found
+ the residual amount to be non-zero. This should mean that a program
+ is issuing a read larger thean the block size on tape. For write
+ not all data made it to tape.
+
+.. Note::
+
+ The in_flight value is incremented when an I/O starts the I/O
+ itself is not added to the statistics until it completes.
+
+The total of read_cnt, write_cnt, and other_cnt may not total to the same
+value as iodone_cnt at the device level. The tape statistics only count
+I/O issued via the st module.
+
+When read the statistics may not be temporally consistent while I/O is in
+progress. The individual values are read and written to atomically however
+when reading them back via sysfs they may be in the process of being
+updated when starting an I/O or when it is completed.
+
+The value shown in in_flight is incremented before any statstics are
+updated and decremented when an I/O completes after updating statistics.
+The value of in_flight is 0 when there are no I/Os outstanding that are
+issued by the st driver. Tape statistics do not take into account any
+I/O performed via the sg device.
+
+BSD and Sys V Semantics
+=======================
+
+The user can choose between these two behaviours of the tape driver by
+defining the value of the symbol ST_SYSV. The semantics differ when a
+file being read is closed. The BSD semantics leaves the tape where it
+currently is whereas the SYS V semantics moves the tape past the next
+filemark unless the filemark has just been crossed.
+
+The default is BSD semantics.
+
+
+Buffering
+=========
+
+The driver tries to do transfers directly to/from user space. If this
+is not possible, a driver buffer allocated at run-time is used. If
+direct i/o is not possible for the whole transfer, the driver buffer
+is used (i.e., bounce buffers for individual pages are not
+used). Direct i/o can be impossible because of several reasons, e.g.:
+
+- one or more pages are at addresses not reachable by the HBA
+- the number of pages in the transfer exceeds the number of
+ scatter/gather segments permitted by the HBA
+- one or more pages can't be locked into memory (should not happen in
+ any reasonable situation)
+
+The size of the driver buffers is always at least one tape block. In fixed
+block mode, the minimum buffer size is defined (in 1024 byte units) by
+ST_FIXED_BUFFER_BLOCKS. With small block size this allows buffering of
+several blocks and using one SCSI read or write to transfer all of the
+blocks. Buffering of data across write calls in fixed block mode is
+allowed if ST_BUFFER_WRITES is non-zero and direct i/o is not used.
+Buffer allocation uses chunks of memory having sizes 2^n * (page
+size). Because of this the actual buffer size may be larger than the
+minimum allowable buffer size.
+
+NOTE that if direct i/o is used, the small writes are not buffered. This may
+cause a surprise when moving from 2.4. There small writes (e.g., tar without
+-b option) may have had good throughput but this is not true any more with
+2.6. Direct i/o can be turned off to solve this problem but a better solution
+is to use bigger write() byte counts (e.g., tar -b 64).
+
+Asynchronous writing. Writing the buffer contents to the tape is
+started and the write call returns immediately. The status is checked
+at the next tape operation. Asynchronous writes are not done with
+direct i/o and not in fixed block mode.
+
+Buffered writes and asynchronous writes may in some rare cases cause
+problems in multivolume operations if there is not enough space on the
+tape after the early-warning mark to flush the driver buffer.
+
+Read ahead for fixed block mode (ST_READ_AHEAD). Filling the buffer is
+attempted even if the user does not want to get all of the data at
+this read command. Should be disabled for those drives that don't like
+a filemark to truncate a read request or that don't like backspacing.
+
+Scatter/gather buffers (buffers that consist of chunks non-contiguous
+in the physical memory) are used if contiguous buffers can't be
+allocated. To support all SCSI adapters (including those not
+supporting scatter/gather), buffer allocation is using the following
+three kinds of chunks:
+
+1. The initial segment that is used for all SCSI adapters including
+ those not supporting scatter/gather. The size of this buffer will be
+ (PAGE_SIZE << ST_FIRST_ORDER) bytes if the system can give a chunk of
+ this size (and it is not larger than the buffer size specified by
+ ST_BUFFER_BLOCKS). If this size is not available, the driver halves
+ the size and tries again until the size of one page. The default
+ settings in st_options.h make the driver to try to allocate all of the
+ buffer as one chunk.
+2. The scatter/gather segments to fill the specified buffer size are
+ allocated so that as many segments as possible are used but the number
+ of segments does not exceed ST_FIRST_SG.
+3. The remaining segments between ST_MAX_SG (or the module parameter
+ max_sg_segs) and the number of segments used in phases 1 and 2
+ are used to extend the buffer at run-time if this is necessary. The
+ number of scatter/gather segments allowed for the SCSI adapter is not
+ exceeded if it is smaller than the maximum number of scatter/gather
+ segments specified. If the maximum number allowed for the SCSI adapter
+ is smaller than the number of segments used in phases 1 and 2,
+ extending the buffer will always fail.
+
+
+EOM Behaviour When Writing
+==========================
+
+When the end of medium early warning is encountered, the current write
+is finished and the number of bytes is returned. The next write
+returns -1 and errno is set to ENOSPC. To enable writing a trailer,
+the next write is allowed to proceed and, if successful, the number of
+bytes is returned. After this, -1 and the number of bytes are
+alternately returned until the physical end of medium (or some other
+error) is encountered.
+
+Module Parameters
+=================
+
+The buffer size, write threshold, and the maximum number of allocated buffers
+are configurable when the driver is loaded as a module. The keywords are:
+
+========================== ===========================================
+buffer_kbs=xxx the buffer size for fixed block mode is set
+ to xxx kilobytes
+write_threshold_kbs=xxx the write threshold in kilobytes set to xxx
+max_sg_segs=xxx the maximum number of scatter/gather
+ segments
+try_direct_io=x try direct transfer between user buffer and
+ tape drive if this is non-zero
+========================== ===========================================
+
+Note that if the buffer size is changed but the write threshold is not
+set, the write threshold is set to the new buffer size - 2 kB.
+
+
+Boot Time Configuration
+=======================
+
+If the driver is compiled into the kernel, the same parameters can be
+also set using, e.g., the LILO command line. The preferred syntax is
+to use the same keyword used when loading as module but prepended
+with 'st.'. For instance, to set the maximum number of scatter/gather
+segments, the parameter 'st.max_sg_segs=xx' should be used (xx is the
+number of scatter/gather segments).
+
+For compatibility, the old syntax from early 2.5 and 2.4 kernel
+versions is supported. The same keywords can be used as when loading
+the driver as module. If several parameters are set, the keyword-value
+pairs are separated with a comma (no spaces allowed). A colon can be
+used instead of the equal mark. The definition is prepended by the
+string st=. Here is an example::
+
+ st=buffer_kbs:64,write_threshold_kbs:60
+
+The following syntax used by the old kernel versions is also supported::
+
+ st=aa[,bb[,dd]]
+
+where:
+
+ - aa is the buffer size for fixed block mode in 1024 byte units
+ - bb is the write threshold in 1024 byte units
+ - dd is the maximum number of scatter/gather segments
+
+
+IOCTLs
+======
+
+The tape is positioned and the drive parameters are set with ioctls
+defined in mtio.h The tape control program 'mt' uses these ioctls. Try
+to find an mt that supports all of the Linux SCSI tape ioctls and
+opens the device for writing if the tape contents will be modified
+(look for a package mt-st* from the Linux ftp sites; the GNU mt does
+not open for writing for, e.g., erase).
+
+The supported ioctls are:
+
+The following use the structure mtop:
+
+MTFSF
+ Space forward over count filemarks. Tape positioned after filemark.
+MTFSFM
+ As above but tape positioned before filemark.
+MTBSF
+ Space backward over count filemarks. Tape positioned before
+ filemark.
+MTBSFM
+ As above but ape positioned after filemark.
+MTFSR
+ Space forward over count records.
+MTBSR
+ Space backward over count records.
+MTFSS
+ Space forward over count setmarks.
+MTBSS
+ Space backward over count setmarks.
+MTWEOF
+ Write count filemarks.
+MTWEOFI
+ Write count filemarks with immediate bit set (i.e., does not
+ wait until data is on tape)
+MTWSM
+ Write count setmarks.
+MTREW
+ Rewind tape.
+MTOFFL
+ Set device off line (often rewind plus eject).
+MTNOP
+ Do nothing except flush the buffers.
+MTRETEN
+ Re-tension tape.
+MTEOM
+ Space to end of recorded data.
+MTERASE
+ Erase tape. If the argument is zero, the short erase command
+ is used. The long erase command is used with all other values
+ of the argument.
+MTSEEK
+ Seek to tape block count. Uses Tandberg-compatible seek (QFA)
+ for SCSI-1 drives and SCSI-2 seek for SCSI-2 drives. The file and
+ block numbers in the status are not valid after a seek.
+MTSETBLK
+ Set the drive block size. Setting to zero sets the drive into
+ variable block mode (if applicable).
+MTSETDENSITY
+ Sets the drive density code to arg. See drive
+ documentation for available codes.
+MTLOCK and MTUNLOCK
+ Explicitly lock/unlock the tape drive door.
+MTLOAD and MTUNLOAD
+ Explicitly load and unload the tape. If the
+ command argument x is between MT_ST_HPLOADER_OFFSET + 1 and
+ MT_ST_HPLOADER_OFFSET + 6, the number x is used sent to the
+ drive with the command and it selects the tape slot to use of
+ HP C1553A changer.
+MTCOMPRESSION
+ Sets compressing or uncompressing drive mode using the
+ SCSI mode page 15. Note that some drives other methods for
+ control of compression. Some drives (like the Exabytes) use
+ density codes for compression control. Some drives use another
+ mode page but this page has not been implemented in the
+ driver. Some drives without compression capability will accept
+ any compression mode without error.
+MTSETPART
+ Moves the tape to the partition given by the argument at the
+ next tape operation. The block at which the tape is positioned
+ is the block where the tape was previously positioned in the
+ new active partition unless the next tape operation is
+ MTSEEK. In this case the tape is moved directly to the block
+ specified by MTSEEK. MTSETPART is inactive unless
+ MT_ST_CAN_PARTITIONS set.
+MTMKPART
+ Formats the tape with one partition (argument zero) or two
+ partitions (argument non-zero). If the argument is positive,
+ it specifies the size of partition 1 in megabytes. For DDS
+ drives and several early drives this is the physically first
+ partition of the tape. If the argument is negative, its absolute
+ value specifies the size of partition 0 in megabytes. This is
+ the physically first partition of many later drives, like the
+ LTO drives from LTO-5 upwards. The drive has to support partitions
+ with size specified by the initiator. Inactive unless
+ MT_ST_CAN_PARTITIONS set.
+MTSETDRVBUFFER
+ Is used for several purposes. The command is obtained from count
+ with mask MT_SET_OPTIONS, the low order bits are used as argument.
+ This command is only allowed for the superuser (root). The
+ subcommands are:
+
+ * 0
+ The drive buffer option is set to the argument. Zero means
+ no buffering.
+ * MT_ST_BOOLEANS
+ Sets the buffering options. The bits are the new states
+ (enabled/disabled) the following options (in the
+ parenthesis is specified whether the option is global or
+ can be specified differently for each mode):
+
+ MT_ST_BUFFER_WRITES
+ write buffering (mode)
+ MT_ST_ASYNC_WRITES
+ asynchronous writes (mode)
+ MT_ST_READ_AHEAD
+ read ahead (mode)
+ MT_ST_TWO_FM
+ writing of two filemarks (global)
+ MT_ST_FAST_EOM
+ using the SCSI spacing to EOD (global)
+ MT_ST_AUTO_LOCK
+ automatic locking of the drive door (global)
+ MT_ST_DEF_WRITES
+ the defaults are meant only for writes (mode)
+ MT_ST_CAN_BSR
+ backspacing over more than one records can
+ be used for repositioning the tape (global)
+ MT_ST_NO_BLKLIMS
+ the driver does not ask the block limits
+ from the drive (block size can be changed only to
+ variable) (global)
+ MT_ST_CAN_PARTITIONS
+ enables support for partitioned
+ tapes (global)
+ MT_ST_SCSI2LOGICAL
+ the logical block number is used in
+ the MTSEEK and MTIOCPOS for SCSI-2 drives instead of
+ the device dependent address. It is recommended to set
+ this flag unless there are tapes using the device
+ dependent (from the old times) (global)
+ MT_ST_SYSV
+ sets the SYSV semantics (mode)
+ MT_ST_NOWAIT
+ enables immediate mode (i.e., don't wait for
+ the command to finish) for some commands (e.g., rewind)
+ MT_ST_NOWAIT_EOF
+ enables immediate filemark mode (i.e. when
+ writing a filemark, don't wait for it to complete). Please
+ see the BASICS note about MTWEOFI with respect to the
+ possible dangers of writing immediate filemarks.
+ MT_ST_SILI
+ enables setting the SILI bit in SCSI commands when
+ reading in variable block mode to enhance performance when
+ reading blocks shorter than the byte count; set this only
+ if you are sure that the drive supports SILI and the HBA
+ correctly returns transfer residuals
+ MT_ST_DEBUGGING
+ debugging (global; debugging must be
+ compiled into the driver)
+
+ * MT_ST_SETBOOLEANS, MT_ST_CLEARBOOLEANS
+ Sets or clears the option bits.
+ * MT_ST_WRITE_THRESHOLD
+ Sets the write threshold for this device to kilobytes
+ specified by the lowest bits.
+ * MT_ST_DEF_BLKSIZE
+ Defines the default block size set automatically. Value
+ 0xffffff means that the default is not used any more.
+ * MT_ST_DEF_DENSITY, MT_ST_DEF_DRVBUFFER
+ Used to set or clear the density (8 bits), and drive buffer
+ state (3 bits). If the value is MT_ST_CLEAR_DEFAULT
+ (0xfffff) the default will not be used any more. Otherwise
+ the lowermost bits of the value contain the new value of
+ the parameter.
+ * MT_ST_DEF_COMPRESSION
+ The compression default will not be used if the value of
+ the lowermost byte is 0xff. Otherwise the lowermost bit
+ contains the new default. If the bits 8-15 are set to a
+ non-zero number, and this number is not 0xff, the number is
+ used as the compression algorithm. The value
+ MT_ST_CLEAR_DEFAULT can be used to clear the compression
+ default.
+ * MT_ST_SET_TIMEOUT
+ Set the normal timeout in seconds for this device. The
+ default is 900 seconds (15 minutes). The timeout should be
+ long enough for the retries done by the device while
+ reading/writing.
+ * MT_ST_SET_LONG_TIMEOUT
+ Set the long timeout that is used for operations that are
+ known to take a long time. The default is 14000 seconds
+ (3.9 hours). For erase this value is further multiplied by
+ eight.
+ * MT_ST_SET_CLN
+ Set the cleaning request interpretation parameters using
+ the lowest 24 bits of the argument. The driver can set the
+ generic status bit GMT_CLN if a cleaning request bit pattern
+ is found from the extended sense data. Many drives set one or
+ more bits in the extended sense data when the drive needs
+ cleaning. The bits are device-dependent. The driver is
+ given the number of the sense data byte (the lowest eight
+ bits of the argument; must be >= 18 (values 1 - 17
+ reserved) and <= the maximum requested sense data sixe),
+ a mask to select the relevant bits (the bits 9-16), and the
+ bit pattern (bits 17-23). If the bit pattern is zero, one
+ or more bits under the mask indicate cleaning request. If
+ the pattern is non-zero, the pattern must match the masked
+ sense data byte.
+
+ (The cleaning bit is set if the additional sense code and
+ qualifier 00h 17h are seen regardless of the setting of
+ MT_ST_SET_CLN.)
+
+The following ioctl uses the structure mtpos:
+
+MTIOCPOS
+ Reads the current position from the drive. Uses
+ Tandberg-compatible QFA for SCSI-1 drives and the SCSI-2
+ command for the SCSI-2 drives.
+
+The following ioctl uses the structure mtget to return the status:
+
+MTIOCGET
+ Returns some status information.
+ The file number and block number within file are returned. The
+ block is -1 when it can't be determined (e.g., after MTBSF).
+ The drive type is either MTISSCSI1 or MTISSCSI2.
+ The number of recovered errors since the previous status call
+ is stored in the lower word of the field mt_erreg.
+ The current block size and the density code are stored in the field
+ mt_dsreg (shifts for the subfields are MT_ST_BLKSIZE_SHIFT and
+ MT_ST_DENSITY_SHIFT).
+ The GMT_xxx status bits reflect the drive status. GMT_DR_OPEN
+ is set if there is no tape in the drive. GMT_EOD means either
+ end of recorded data or end of tape. GMT_EOT means end of tape.
+
+
+Miscellaneous Compile Options
+=============================
+
+The recovered write errors are considered fatal if ST_RECOVERED_WRITE_FATAL
+is defined.
+
+The maximum number of tape devices is determined by the define
+ST_MAX_TAPES. If more tapes are detected at driver initialization, the
+maximum is adjusted accordingly.
+
+Immediate return from tape positioning SCSI commands can be enabled by
+defining ST_NOWAIT. If this is defined, the user should take care that
+the next tape operation is not started before the previous one has
+finished. The drives and SCSI adapters should handle this condition
+gracefully, but some drive/adapter combinations are known to hang the
+SCSI bus in this case.
+
+The MTEOM command is by default implemented as spacing over 32767
+filemarks. With this method the file number in the status is
+correct. The user can request using direct spacing to EOD by setting
+ST_FAST_EOM 1 (or using the MT_ST_OPTIONS ioctl). In this case the file
+number will be invalid.
+
+When using read ahead or buffered writes the position within the file
+may not be correct after the file is closed (correct position may
+require backspacing over more than one record). The correct position
+within file can be obtained if ST_IN_FILE_POS is defined at compile
+time or the MT_ST_CAN_BSR bit is set for the drive with an ioctl.
+(The driver always backs over a filemark crossed by read ahead if the
+user does not request data that far.)
+
+
+Debugging Hints
+===============
+
+Debugging code is now compiled in by default but debugging is turned off
+with the kernel module parameter debug_flag defaulting to 0. Debugging
+can still be switched on and off with an ioctl. To enable debug at
+module load time add debug_flag=1 to the module load options, the
+debugging output is not voluminous. Debugging can also be enabled
+and disabled by writing a '0' (disable) or '1' (enable) to the sysfs
+file /sys/bus/scsi/drivers/st/debug_flag.
+
+If the tape seems to hang, I would be very interested to hear where
+the driver is waiting. With the command 'ps -l' you can see the state
+of the process using the tape. If the state is D, the process is
+waiting for something. The field WCHAN tells where the driver is
+waiting. If you have the current System.map in the correct place (in
+/boot for the procps I use) or have updated /etc/psdatabase (for kmem
+ps), ps writes the function name in the WCHAN field. If not, you have
+to look up the function from System.map.
+
+Note also that the timeouts are very long compared to most other
+drivers. This means that the Linux driver may appear hung although the
+real reason is that the tape firmware has got confused.
+++ /dev/null
-This file contains brief information about the SCSI tape driver.
-The driver is currently maintained by Kai Mäkisara (email
-Kai.Makisara@kolumbus.fi)
-
-Last modified: Tue Feb 9 21:54:16 2016 by kai.makisara
-
-
-BASICS
-
-The driver is generic, i.e., it does not contain any code tailored
-to any specific tape drive. The tape parameters can be specified with
-one of the following three methods:
-
-1. Each user can specify the tape parameters he/she wants to use
-directly with ioctls. This is administratively a very simple and
-flexible method and applicable to single-user workstations. However,
-in a multiuser environment the next user finds the tape parameters in
-state the previous user left them.
-
-2. The system manager (root) can define default values for some tape
-parameters, like block size and density using the MTSETDRVBUFFER ioctl.
-These parameters can be programmed to come into effect either when a
-new tape is loaded into the drive or if writing begins at the
-beginning of the tape. The second method is applicable if the tape
-drive performs auto-detection of the tape format well (like some
-QIC-drives). The result is that any tape can be read, writing can be
-continued using existing format, and the default format is used if
-the tape is rewritten from the beginning (or a new tape is written
-for the first time). The first method is applicable if the drive
-does not perform auto-detection well enough and there is a single
-"sensible" mode for the device. An example is a DAT drive that is
-used only in variable block mode (I don't know if this is sensible
-or not :-).
-
-The user can override the parameters defined by the system
-manager. The changes persist until the defaults again come into
-effect.
-
-3. By default, up to four modes can be defined and selected using the minor
-number (bits 5 and 6). The number of modes can be changed by changing
-ST_NBR_MODE_BITS in st.h. Mode 0 corresponds to the defaults discussed
-above. Additional modes are dormant until they are defined by the
-system manager (root). When specification of a new mode is started,
-the configuration of mode 0 is used to provide a starting point for
-definition of the new mode.
-
-Using the modes allows the system manager to give the users choices
-over some of the buffering parameters not directly accessible to the
-users (buffered and asynchronous writes). The modes also allow choices
-between formats in multi-tape operations (the explicitly overridden
-parameters are reset when a new tape is loaded).
-
-If more than one mode is used, all modes should contain definitions
-for the same set of parameters.
-
-Many Unices contain internal tables that associate different modes to
-supported devices. The Linux SCSI tape driver does not contain such
-tables (and will not do that in future). Instead of that, a utility
-program can be made that fetches the inquiry data sent by the device,
-scans its database, and sets up the modes using the ioctls. Another
-alternative is to make a small script that uses mt to set the defaults
-tailored to the system.
-
-The driver supports fixed and variable block size (within buffer
-limits). Both the auto-rewind (minor equals device number) and
-non-rewind devices (minor is 128 + device number) are implemented.
-
-In variable block mode, the byte count in write() determines the size
-of the physical block on tape. When reading, the drive reads the next
-tape block and returns to the user the data if the read() byte count
-is at least the block size. Otherwise, error ENOMEM is returned.
-
-In fixed block mode, the data transfer between the drive and the
-driver is in multiples of the block size. The write() byte count must
-be a multiple of the block size. This is not required when reading but
-may be advisable for portability.
-
-Support is provided for changing the tape partition and partitioning
-of the tape with one or two partitions. By default support for
-partitioned tape is disabled for each driver and it can be enabled
-with the ioctl MTSETDRVBUFFER.
-
-By default the driver writes one filemark when the device is closed after
-writing and the last operation has been a write. Two filemarks can be
-optionally written. In both cases end of data is signified by
-returning zero bytes for two consecutive reads.
-
-Writing filemarks without the immediate bit set in the SCSI command block acts
-as a synchronization point, i.e., all remaining data form the drive buffers is
-written to tape before the command returns. This makes sure that write errors
-are caught at that point, but this takes time. In some applications, several
-consecutive files must be written fast. The MTWEOFI operation can be used to
-write the filemarks without flushing the drive buffer. Writing filemark at
-close() is always flushing the drive buffers. However, if the previous
-operation is MTWEOFI, close() does not write a filemark. This can be used if
-the program wants to close/open the tape device between files and wants to
-skip waiting.
-
-If rewind, offline, bsf, or seek is done and previous tape operation was
-write, a filemark is written before moving tape.
-
-The compile options are defined in the file linux/drivers/scsi/st_options.h.
-
-4. If the open option O_NONBLOCK is used, open succeeds even if the
-drive is not ready. If O_NONBLOCK is not used, the driver waits for
-the drive to become ready. If this does not happen in ST_BLOCK_SECONDS
-seconds, open fails with the errno value EIO. With O_NONBLOCK the
-device can be opened for writing even if there is a write protected
-tape in the drive (commands trying to write something return error if
-attempted).
-
-
-MINOR NUMBERS
-
-The tape driver currently supports up to 2^17 drives if 4 modes for
-each drive are used.
-
-The minor numbers consist of the following bit fields:
-
-dev_upper non-rew mode dev-lower
- 20 - 8 7 6 5 4 0
-The non-rewind bit is always bit 7 (the uppermost bit in the lowermost
-byte). The bits defining the mode are below the non-rewind bit. The
-remaining bits define the tape device number. This numbering is
-backward compatible with the numbering used when the minor number was
-only 8 bits wide.
-
-
-SYSFS SUPPORT
-
-The driver creates the directory /sys/class/scsi_tape and populates it with
-directories corresponding to the existing tape devices. There are autorewind
-and non-rewind entries for each mode. The names are stxy and nstxy, where x
-is the tape number and y a character corresponding to the mode (none, l, m,
-a). For example, the directories for the first tape device are (assuming four
-modes): st0 nst0 st0l nst0l st0m nst0m st0a nst0a.
-
-Each directory contains the entries: default_blksize default_compression
-default_density defined dev device driver. The file 'defined' contains 1
-if the mode is defined and zero if not defined. The files 'default_*' contain
-the defaults set by the user. The value -1 means the default is not set. The
-file 'dev' contains the device numbers corresponding to this device. The links
-'device' and 'driver' point to the SCSI device and driver entries.
-
-Each directory also contains the entry 'options' which shows the currently
-enabled driver and mode options. The value in the file is a bit mask where the
-bit definitions are the same as those used with MTSETDRVBUFFER in setting the
-options.
-
-A link named 'tape' is made from the SCSI device directory to the class
-directory corresponding to the mode 0 auto-rewind device (e.g., st0).
-
-
-SYSFS AND STATISTICS FOR TAPE DEVICES
-
-The st driver maintains statistics for tape drives inside the sysfs filesystem.
-The following method can be used to locate the statistics that are
-available (assuming that sysfs is mounted at /sys):
-
-1. Use opendir(3) on the directory /sys/class/scsi_tape
-2. Use readdir(3) to read the directory contents
-3. Use regcomp(3)/regexec(3) to match directory entries to the extended
- regular expression "^st[0-9]+$"
-4. Access the statistics from the /sys/class/scsi_tape/<match>/stats
- directory (where <match> is a directory entry from /sys/class/scsi_tape
- that matched the extended regular expression)
-
-The reason for using this approach is that all the character devices
-pointing to the same tape drive use the same statistics. That means
-that st0 would have the same statistics as nst0.
-
-The directory contains the following statistics files:
-
-1. in_flight - The number of I/Os currently outstanding to this device.
-2. io_ns - The amount of time spent waiting (in nanoseconds) for all I/O
- to complete (including read and write). This includes tape movement
- commands such as seeking between file or set marks and implicit tape
- movement such as when rewind on close tape devices are used.
-3. other_cnt - The number of I/Os issued to the tape drive other than read or
- write commands. The time taken to complete these commands uses the
- following calculation io_ms-read_ms-write_ms.
-4. read_byte_cnt - The number of bytes read from the tape drive.
-5. read_cnt - The number of read requests issued to the tape drive.
-6. read_ns - The amount of time (in nanoseconds) spent waiting for read
- requests to complete.
-7. write_byte_cnt - The number of bytes written to the tape drive.
-8. write_cnt - The number of write requests issued to the tape drive.
-9. write_ns - The amount of time (in nanoseconds) spent waiting for write
- requests to complete.
-10. resid_cnt - The number of times during a read or write we found
- the residual amount to be non-zero. This should mean that a program
- is issuing a read larger thean the block size on tape. For write
- not all data made it to tape.
-
-Note: The in_flight value is incremented when an I/O starts the I/O
-itself is not added to the statistics until it completes.
-
-The total of read_cnt, write_cnt, and other_cnt may not total to the same
-value as iodone_cnt at the device level. The tape statistics only count
-I/O issued via the st module.
-
-When read the statistics may not be temporally consistent while I/O is in
-progress. The individual values are read and written to atomically however
-when reading them back via sysfs they may be in the process of being
-updated when starting an I/O or when it is completed.
-
-The value shown in in_flight is incremented before any statstics are
-updated and decremented when an I/O completes after updating statistics.
-The value of in_flight is 0 when there are no I/Os outstanding that are
-issued by the st driver. Tape statistics do not take into account any
-I/O performed via the sg device.
-
-BSD AND SYS V SEMANTICS
-
-The user can choose between these two behaviours of the tape driver by
-defining the value of the symbol ST_SYSV. The semantics differ when a
-file being read is closed. The BSD semantics leaves the tape where it
-currently is whereas the SYS V semantics moves the tape past the next
-filemark unless the filemark has just been crossed.
-
-The default is BSD semantics.
-
-
-BUFFERING
-
-The driver tries to do transfers directly to/from user space. If this
-is not possible, a driver buffer allocated at run-time is used. If
-direct i/o is not possible for the whole transfer, the driver buffer
-is used (i.e., bounce buffers for individual pages are not
-used). Direct i/o can be impossible because of several reasons, e.g.:
-- one or more pages are at addresses not reachable by the HBA
-- the number of pages in the transfer exceeds the number of
- scatter/gather segments permitted by the HBA
-- one or more pages can't be locked into memory (should not happen in
- any reasonable situation)
-
-The size of the driver buffers is always at least one tape block. In fixed
-block mode, the minimum buffer size is defined (in 1024 byte units) by
-ST_FIXED_BUFFER_BLOCKS. With small block size this allows buffering of
-several blocks and using one SCSI read or write to transfer all of the
-blocks. Buffering of data across write calls in fixed block mode is
-allowed if ST_BUFFER_WRITES is non-zero and direct i/o is not used.
-Buffer allocation uses chunks of memory having sizes 2^n * (page
-size). Because of this the actual buffer size may be larger than the
-minimum allowable buffer size.
-
-NOTE that if direct i/o is used, the small writes are not buffered. This may
-cause a surprise when moving from 2.4. There small writes (e.g., tar without
--b option) may have had good throughput but this is not true any more with
-2.6. Direct i/o can be turned off to solve this problem but a better solution
-is to use bigger write() byte counts (e.g., tar -b 64).
-
-Asynchronous writing. Writing the buffer contents to the tape is
-started and the write call returns immediately. The status is checked
-at the next tape operation. Asynchronous writes are not done with
-direct i/o and not in fixed block mode.
-
-Buffered writes and asynchronous writes may in some rare cases cause
-problems in multivolume operations if there is not enough space on the
-tape after the early-warning mark to flush the driver buffer.
-
-Read ahead for fixed block mode (ST_READ_AHEAD). Filling the buffer is
-attempted even if the user does not want to get all of the data at
-this read command. Should be disabled for those drives that don't like
-a filemark to truncate a read request or that don't like backspacing.
-
-Scatter/gather buffers (buffers that consist of chunks non-contiguous
-in the physical memory) are used if contiguous buffers can't be
-allocated. To support all SCSI adapters (including those not
-supporting scatter/gather), buffer allocation is using the following
-three kinds of chunks:
-1. The initial segment that is used for all SCSI adapters including
-those not supporting scatter/gather. The size of this buffer will be
-(PAGE_SIZE << ST_FIRST_ORDER) bytes if the system can give a chunk of
-this size (and it is not larger than the buffer size specified by
-ST_BUFFER_BLOCKS). If this size is not available, the driver halves
-the size and tries again until the size of one page. The default
-settings in st_options.h make the driver to try to allocate all of the
-buffer as one chunk.
-2. The scatter/gather segments to fill the specified buffer size are
-allocated so that as many segments as possible are used but the number
-of segments does not exceed ST_FIRST_SG.
-3. The remaining segments between ST_MAX_SG (or the module parameter
-max_sg_segs) and the number of segments used in phases 1 and 2
-are used to extend the buffer at run-time if this is necessary. The
-number of scatter/gather segments allowed for the SCSI adapter is not
-exceeded if it is smaller than the maximum number of scatter/gather
-segments specified. If the maximum number allowed for the SCSI adapter
-is smaller than the number of segments used in phases 1 and 2,
-extending the buffer will always fail.
-
-
-EOM BEHAVIOUR WHEN WRITING
-
-When the end of medium early warning is encountered, the current write
-is finished and the number of bytes is returned. The next write
-returns -1 and errno is set to ENOSPC. To enable writing a trailer,
-the next write is allowed to proceed and, if successful, the number of
-bytes is returned. After this, -1 and the number of bytes are
-alternately returned until the physical end of medium (or some other
-error) is encountered.
-
-
-MODULE PARAMETERS
-
-The buffer size, write threshold, and the maximum number of allocated buffers
-are configurable when the driver is loaded as a module. The keywords are:
-
-buffer_kbs=xxx the buffer size for fixed block mode is set
- to xxx kilobytes
-write_threshold_kbs=xxx the write threshold in kilobytes set to xxx
-max_sg_segs=xxx the maximum number of scatter/gather
- segments
-try_direct_io=x try direct transfer between user buffer and
- tape drive if this is non-zero
-
-Note that if the buffer size is changed but the write threshold is not
-set, the write threshold is set to the new buffer size - 2 kB.
-
-
-BOOT TIME CONFIGURATION
-
-If the driver is compiled into the kernel, the same parameters can be
-also set using, e.g., the LILO command line. The preferred syntax is
-to use the same keyword used when loading as module but prepended
-with 'st.'. For instance, to set the maximum number of scatter/gather
-segments, the parameter 'st.max_sg_segs=xx' should be used (xx is the
-number of scatter/gather segments).
-
-For compatibility, the old syntax from early 2.5 and 2.4 kernel
-versions is supported. The same keywords can be used as when loading
-the driver as module. If several parameters are set, the keyword-value
-pairs are separated with a comma (no spaces allowed). A colon can be
-used instead of the equal mark. The definition is prepended by the
-string st=. Here is an example:
-
- st=buffer_kbs:64,write_threshold_kbs:60
-
-The following syntax used by the old kernel versions is also supported:
-
- st=aa[,bb[,dd]]
-
-where
- aa is the buffer size for fixed block mode in 1024 byte units
- bb is the write threshold in 1024 byte units
- dd is the maximum number of scatter/gather segments
-
-
-IOCTLS
-
-The tape is positioned and the drive parameters are set with ioctls
-defined in mtio.h The tape control program 'mt' uses these ioctls. Try
-to find an mt that supports all of the Linux SCSI tape ioctls and
-opens the device for writing if the tape contents will be modified
-(look for a package mt-st* from the Linux ftp sites; the GNU mt does
-not open for writing for, e.g., erase).
-
-The supported ioctls are:
-
-The following use the structure mtop:
-
-MTFSF Space forward over count filemarks. Tape positioned after filemark.
-MTFSFM As above but tape positioned before filemark.
-MTBSF Space backward over count filemarks. Tape positioned before
- filemark.
-MTBSFM As above but ape positioned after filemark.
-MTFSR Space forward over count records.
-MTBSR Space backward over count records.
-MTFSS Space forward over count setmarks.
-MTBSS Space backward over count setmarks.
-MTWEOF Write count filemarks.
-MTWEOFI Write count filemarks with immediate bit set (i.e., does not
- wait until data is on tape)
-MTWSM Write count setmarks.
-MTREW Rewind tape.
-MTOFFL Set device off line (often rewind plus eject).
-MTNOP Do nothing except flush the buffers.
-MTRETEN Re-tension tape.
-MTEOM Space to end of recorded data.
-MTERASE Erase tape. If the argument is zero, the short erase command
- is used. The long erase command is used with all other values
- of the argument.
-MTSEEK Seek to tape block count. Uses Tandberg-compatible seek (QFA)
- for SCSI-1 drives and SCSI-2 seek for SCSI-2 drives. The file and
- block numbers in the status are not valid after a seek.
-MTSETBLK Set the drive block size. Setting to zero sets the drive into
- variable block mode (if applicable).
-MTSETDENSITY Sets the drive density code to arg. See drive
- documentation for available codes.
-MTLOCK and MTUNLOCK Explicitly lock/unlock the tape drive door.
-MTLOAD and MTUNLOAD Explicitly load and unload the tape. If the
- command argument x is between MT_ST_HPLOADER_OFFSET + 1 and
- MT_ST_HPLOADER_OFFSET + 6, the number x is used sent to the
- drive with the command and it selects the tape slot to use of
- HP C1553A changer.
-MTCOMPRESSION Sets compressing or uncompressing drive mode using the
- SCSI mode page 15. Note that some drives other methods for
- control of compression. Some drives (like the Exabytes) use
- density codes for compression control. Some drives use another
- mode page but this page has not been implemented in the
- driver. Some drives without compression capability will accept
- any compression mode without error.
-MTSETPART Moves the tape to the partition given by the argument at the
- next tape operation. The block at which the tape is positioned
- is the block where the tape was previously positioned in the
- new active partition unless the next tape operation is
- MTSEEK. In this case the tape is moved directly to the block
- specified by MTSEEK. MTSETPART is inactive unless
- MT_ST_CAN_PARTITIONS set.
-MTMKPART Formats the tape with one partition (argument zero) or two
- partitions (argument non-zero). If the argument is positive,
- it specifies the size of partition 1 in megabytes. For DDS
- drives and several early drives this is the physically first
- partition of the tape. If the argument is negative, its absolute
- value specifies the size of partition 0 in megabytes. This is
- the physically first partition of many later drives, like the
- LTO drives from LTO-5 upwards. The drive has to support partitions
- with size specified by the initiator. Inactive unless
- MT_ST_CAN_PARTITIONS set.
-MTSETDRVBUFFER
- Is used for several purposes. The command is obtained from count
- with mask MT_SET_OPTIONS, the low order bits are used as argument.
- This command is only allowed for the superuser (root). The
- subcommands are:
- 0
- The drive buffer option is set to the argument. Zero means
- no buffering.
- MT_ST_BOOLEANS
- Sets the buffering options. The bits are the new states
- (enabled/disabled) the following options (in the
- parenthesis is specified whether the option is global or
- can be specified differently for each mode):
- MT_ST_BUFFER_WRITES write buffering (mode)
- MT_ST_ASYNC_WRITES asynchronous writes (mode)
- MT_ST_READ_AHEAD read ahead (mode)
- MT_ST_TWO_FM writing of two filemarks (global)
- MT_ST_FAST_EOM using the SCSI spacing to EOD (global)
- MT_ST_AUTO_LOCK automatic locking of the drive door (global)
- MT_ST_DEF_WRITES the defaults are meant only for writes (mode)
- MT_ST_CAN_BSR backspacing over more than one records can
- be used for repositioning the tape (global)
- MT_ST_NO_BLKLIMS the driver does not ask the block limits
- from the drive (block size can be changed only to
- variable) (global)
- MT_ST_CAN_PARTITIONS enables support for partitioned
- tapes (global)
- MT_ST_SCSI2LOGICAL the logical block number is used in
- the MTSEEK and MTIOCPOS for SCSI-2 drives instead of
- the device dependent address. It is recommended to set
- this flag unless there are tapes using the device
- dependent (from the old times) (global)
- MT_ST_SYSV sets the SYSV semantics (mode)
- MT_ST_NOWAIT enables immediate mode (i.e., don't wait for
- the command to finish) for some commands (e.g., rewind)
- MT_ST_NOWAIT_EOF enables immediate filemark mode (i.e. when
- writing a filemark, don't wait for it to complete). Please
- see the BASICS note about MTWEOFI with respect to the
- possible dangers of writing immediate filemarks.
- MT_ST_SILI enables setting the SILI bit in SCSI commands when
- reading in variable block mode to enhance performance when
- reading blocks shorter than the byte count; set this only
- if you are sure that the drive supports SILI and the HBA
- correctly returns transfer residuals
- MT_ST_DEBUGGING debugging (global; debugging must be
- compiled into the driver)
- MT_ST_SETBOOLEANS
- MT_ST_CLEARBOOLEANS
- Sets or clears the option bits.
- MT_ST_WRITE_THRESHOLD
- Sets the write threshold for this device to kilobytes
- specified by the lowest bits.
- MT_ST_DEF_BLKSIZE
- Defines the default block size set automatically. Value
- 0xffffff means that the default is not used any more.
- MT_ST_DEF_DENSITY
- MT_ST_DEF_DRVBUFFER
- Used to set or clear the density (8 bits), and drive buffer
- state (3 bits). If the value is MT_ST_CLEAR_DEFAULT
- (0xfffff) the default will not be used any more. Otherwise
- the lowermost bits of the value contain the new value of
- the parameter.
- MT_ST_DEF_COMPRESSION
- The compression default will not be used if the value of
- the lowermost byte is 0xff. Otherwise the lowermost bit
- contains the new default. If the bits 8-15 are set to a
- non-zero number, and this number is not 0xff, the number is
- used as the compression algorithm. The value
- MT_ST_CLEAR_DEFAULT can be used to clear the compression
- default.
- MT_ST_SET_TIMEOUT
- Set the normal timeout in seconds for this device. The
- default is 900 seconds (15 minutes). The timeout should be
- long enough for the retries done by the device while
- reading/writing.
- MT_ST_SET_LONG_TIMEOUT
- Set the long timeout that is used for operations that are
- known to take a long time. The default is 14000 seconds
- (3.9 hours). For erase this value is further multiplied by
- eight.
- MT_ST_SET_CLN
- Set the cleaning request interpretation parameters using
- the lowest 24 bits of the argument. The driver can set the
- generic status bit GMT_CLN if a cleaning request bit pattern
- is found from the extended sense data. Many drives set one or
- more bits in the extended sense data when the drive needs
- cleaning. The bits are device-dependent. The driver is
- given the number of the sense data byte (the lowest eight
- bits of the argument; must be >= 18 (values 1 - 17
- reserved) and <= the maximum requested sense data sixe),
- a mask to select the relevant bits (the bits 9-16), and the
- bit pattern (bits 17-23). If the bit pattern is zero, one
- or more bits under the mask indicate cleaning request. If
- the pattern is non-zero, the pattern must match the masked
- sense data byte.
-
- (The cleaning bit is set if the additional sense code and
- qualifier 00h 17h are seen regardless of the setting of
- MT_ST_SET_CLN.)
-
-The following ioctl uses the structure mtpos:
-MTIOCPOS Reads the current position from the drive. Uses
- Tandberg-compatible QFA for SCSI-1 drives and the SCSI-2
- command for the SCSI-2 drives.
-
-The following ioctl uses the structure mtget to return the status:
-MTIOCGET Returns some status information.
- The file number and block number within file are returned. The
- block is -1 when it can't be determined (e.g., after MTBSF).
- The drive type is either MTISSCSI1 or MTISSCSI2.
- The number of recovered errors since the previous status call
- is stored in the lower word of the field mt_erreg.
- The current block size and the density code are stored in the field
- mt_dsreg (shifts for the subfields are MT_ST_BLKSIZE_SHIFT and
- MT_ST_DENSITY_SHIFT).
- The GMT_xxx status bits reflect the drive status. GMT_DR_OPEN
- is set if there is no tape in the drive. GMT_EOD means either
- end of recorded data or end of tape. GMT_EOT means end of tape.
-
-
-MISCELLANEOUS COMPILE OPTIONS
-
-The recovered write errors are considered fatal if ST_RECOVERED_WRITE_FATAL
-is defined.
-
-The maximum number of tape devices is determined by the define
-ST_MAX_TAPES. If more tapes are detected at driver initialization, the
-maximum is adjusted accordingly.
-
-Immediate return from tape positioning SCSI commands can be enabled by
-defining ST_NOWAIT. If this is defined, the user should take care that
-the next tape operation is not started before the previous one has
-finished. The drives and SCSI adapters should handle this condition
-gracefully, but some drive/adapter combinations are known to hang the
-SCSI bus in this case.
-
-The MTEOM command is by default implemented as spacing over 32767
-filemarks. With this method the file number in the status is
-correct. The user can request using direct spacing to EOD by setting
-ST_FAST_EOM 1 (or using the MT_ST_OPTIONS ioctl). In this case the file
-number will be invalid.
-
-When using read ahead or buffered writes the position within the file
-may not be correct after the file is closed (correct position may
-require backspacing over more than one record). The correct position
-within file can be obtained if ST_IN_FILE_POS is defined at compile
-time or the MT_ST_CAN_BSR bit is set for the drive with an ioctl.
-(The driver always backs over a filemark crossed by read ahead if the
-user does not request data that far.)
-
-
-DEBUGGING HINTS
-
-Debugging code is now compiled in by default but debugging is turned off
-with the kernel module parameter debug_flag defaulting to 0. Debugging
-can still be switched on and off with an ioctl. To enable debug at
-module load time add debug_flag=1 to the module load options, the
-debugging output is not voluminous. Debugging can also be enabled
-and disabled by writing a '0' (disable) or '1' (enable) to the sysfs
-file /sys/bus/scsi/drivers/st/debug_flag.
-
-If the tape seems to hang, I would be very interested to hear where
-the driver is waiting. With the command 'ps -l' you can see the state
-of the process using the tape. If the state is D, the process is
-waiting for something. The field WCHAN tells where the driver is
-waiting. If you have the current System.map in the correct place (in
-/boot for the procps I use) or have updated /etc/psdatabase (for kmem
-ps), ps writes the function name in the WCHAN field. If not, you have
-to look up the function from System.map.
-
-Note also that the timeouts are very long compared to most other
-drivers. This means that the Linux driver may appear hung although the
-real reason is that the tape firmware has got confused.
M: Kai Mäkisara <Kai.Makisara@kolumbus.fi>
L: linux-scsi@vger.kernel.org
S: Maintained
-F: Documentation/scsi/st.txt
+F: Documentation/scsi/st.rst
F: drivers/scsi/st.*
F: drivers/scsi/st_*.h
If you want to use a SCSI tape drive under Linux, say Y and read the
SCSI-HOWTO, available from
<http://www.tldp.org/docs.html#howto>, and
- <file:Documentation/scsi/st.txt> in the kernel source. This is NOT
+ <file:Documentation/scsi/st.rst> in the kernel source. This is NOT
for SCSI CD-ROMs.
To compile this driver as a module, choose M here and read
// SPDX-License-Identifier: GPL-2.0-only
/*
SCSI Tape Driver for Linux version 1.1 and newer. See the accompanying
- file Documentation/scsi/st.txt for more information.
+ file Documentation/scsi/st.rst for more information.
History:
Rewritten from Dwayne Forsyth's SCSI tape driver by Kai Makisara.
projects / linux-2.6-microblaze.git / commitdiff