Import of Linux/MIPS 2.1.14

1 files changed, 195 insertions, 36 deletions

diff --git a/drivers/scsi/README.st b/drivers/scsi/README.st
index cce8d031f..864836cc1 100644
--- a/drivers/scsi/README.st
+++ b/drivers/scsi/README.st
@@ -1,36 +1,102 @@
 This file contains brief information about the SCSI tape driver.
-Last modified: Tue Jan 10 21:32:35 1995 by root@kai.home
+The driver is currently maintained by Kai M{kisara (email
+Kai.Makisara@metla.fi)
+
+Last modified: Sun Jun 30 15:47:14 1996 by root@kai.makisara.fi
+
 
 BASICS
 
-The driver is generic. The state of a drive is not modified when the
-driver is initialized or a device is opened. The mode parameters of the
-drive can be modified with ioctls. 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.
+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. Up to four modes can be defined and selected using the minor number
+(bits 5 and 6). 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.
+
+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.
 
+The compile options are defined in the file linux/drivers/scsi/st_options.h.
+
+
 BUFFERING
 
-The driver uses a buffer allocated at system initialization. The size
-of the buffer is selectable at compile and/or boot time. The buffer is
-used to store the data being transferred to/from the SCSI adapter. The
-following buffering options are selectable at compile time and/or at run
-time (via ioctl):
+The driver uses tape buffers allocated either at system initialization
+or at run-time when needed. One buffer is used for each open tape
+device. The size of the buffers is selectable at compile and/or boot
+time. The buffers are used to store the data being transferred to/from
+the SCSI adapter. The following buffering options are selectable at
+compile time and/or at run time (via ioctl):
 
-Buffering of data to be written across write calls for fixed block
-mode (define ST_BUFFER_WRITES). This should be disabled if reliable
-detection of end of media (EOM) for fixed block mode is desired.
+Buffering of data across write calls in fixed block mode (define
+ST_BUFFER_WRITES).
 
 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. Should not used if reliable EOM detection
-is desired.
+at the next tape operation.
+
+Buffered writes and asynchronous writes may in some rare cases cause
+problems in multivolume operations if there is not enough space 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
@@ -38,10 +104,33 @@ 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.
 
 The buffer size is defined (in 1024 byte units) by ST_BUFFER_BLOCKS or
-at boot time. The maximum number of buffers allocated is defined by
-ST_MAX_BUFFERS. One buffer is allocated for each detected drive up to
-the maximum. The threshold for triggering asynchronous write is
-defined by ST_WRITE_THRESHOLD.
+at boot time. If this size is not enough, the driver tries to allocate
+a large enough temporary buffer that is released when the device is
+closed. The maximum buffer size is defined by the kernel memory
+allocation (currently 256 kB for Alphas and 128 kB for other
+architectures).
+
+Allocation of the buffers is done at run-time when they are
+needed. Allocation of the specified number of buffers can be done at
+initialization if ST_RUNTIME_BUFFERS is defined non-zero. The
+advantage of run-time allocation is that memory is not wasted for
+buffers not being used. The disadvantage is that there may not be
+memory available at the time when a buffer is needed for the first
+time (once a buffer is allocated, it is not released).
+
+The maximum number of buffers allocated at initialization is defined by
+ST_MAX_BUFFERS. One buffer is allocated for each drive detected when
+the driver is initialized up to the maximum. The minimum number of
+allocated buffers is ST_EXTRA_DEVS (in hosts.h). This ensures some
+functionality also for the drives found after tape driver
+initialization (a SCSI adapter driver is loaded as a module). The
+default for ST_EXTRA_DEVS is two. The driver tries to allocate new
+buffers at run-time if necessary.
+
+The threshold for triggering asynchronous write in fixed block mode
+is defined by ST_WRITE_THRESHOLD. This may be optimized for each
+use pattern. The default triggers asynchronous write after three
+default sized writes (10 kB) from tar.
 
 
 BOOT TIME CONFIGURATION
@@ -86,7 +175,7 @@ MTWSM   Write count setmarks.
 MTREW   Rewind tape.
 MTOFFL  Set device off line (often rewind plus eject).
 MTNOP   Do nothing except flush the buffers.
-MTRETEN Retension tape.
+MTRETEN Re-tension tape.
 MTEOM   Space to end of recorded data.
 MTERASE Erase tape.
 MTSEEK	Seek to tape block count. Uses Tandberg-compatible seek (QFA)
@@ -96,24 +185,78 @@ 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.
+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 things. The command is obtained from count
+	Is used for several purposes. The command is obtained from count
         with mask MT_SET_OPTIONS, the low order bits are used as argument.
-	The subcommands are:
+	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) of the write buffering (MT_ST_BUFFER_WRITES),
-           asynchronous writes (MT_ST_ASYNC_WRITES), read ahead
-           (MT_ST_READ_AHEAD), writing of two filemark (ST_TWO_FM),
-	   using the SCSI spacing to EOD (MT_ST_FAST_EOM), and
-	   debugging (MT_ST_DEBUGGING ; debugging must be compiled into the
-	   driver).
+           (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_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
+	MT_ST_DEF_COMPRESSION
+	   Used to set or clear the density (8 bits), drive buffer
+	   state (3 bits), and compression (single bit). If the value is
+	   MT_ST_CLEAR_DEFAULT (0xfffff), the default will not be used
+	   any more. Otherwise the lower-most bits of the value contain
+	   the new value of the parameter.
 
 The following ioctl uses the structure mtpos:
 MTIOCPOS Reads the current position from the drive. Uses
@@ -134,14 +277,31 @@ MTIOCGET Returns some status information.
 	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.
 
+The following ioctls use the structure mtlocation that contains both
+the block number and the partition number. These ioctls are available
+only for SCSI-2 tape drives and the block number is the
+device-independent logical block number defined by the standard.
+
+MTGETLOC Returns the current block and partition number.
+MTSETLOC Sets the tape to the block and partition specified by the
+	arguments.
+
 
 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.
+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
@@ -152,8 +312,7 @@ 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. (The
-driver always backs over a filemark crossed by read ahead if the user
-does not request data that far.)
-
-Kai M{kisara
+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.)