593 lines
28 KiB
Plaintext
593 lines
28 KiB
Plaintext
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.
|