st.txt

linux 内核源代码

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.
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 (the argument gives in megabytes the size of
	partition 1 that is physically the first partition of the
	tape). 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_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

To enable debugging messages, edit st.c and #define DEBUG 1. As seen
above, debugging can be switched off with an ioctl if debugging is
compiled into the driver. The debugging output is not voluminous.

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.