patch-1.3.85 linux/drivers/scsi/README.st

• Lines: 164
• Date: Mon Apr 8 11:22:20 1996
• Orig file: v1.3.84/linux/drivers/scsi/README.st
• Orig date: Sun Dec 17 10:59:24 1995

diff -u --recursive --new-file v1.3.84/linux/drivers/scsi/README.st linux/drivers/scsi/README.st
@@ -1,14 +1,66 @@
 This file contains brief information about the SCSI tape driver.
-Last modified: Sun Nov 26 12:54:21 1995 by root@kai.makisara.fi
+Last modified: Mon Apr  8 09:34:33 1996 by makisara@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.
 
 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
@@ -17,6 +69,7 @@
 
 The compile options are defined in the file linux/drivers/scsi/st_options.h.
 
+
 BUFFERING
 
 The driver uses tape buffers allocated either at system initialization
@@ -112,7 +165,7 @@
 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)
@@ -122,25 +175,54 @@
         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.
 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), automatic
-	   locking of the drive door (MT_ST_AUTO_LOCK) 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 (global)
+             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 records can be used for
+		repositioning the tape (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
@@ -168,7 +250,7 @@
 is defined.
 
 The maximum number of tape devices is determined by the define
-ST_MAX_TAPES. If more tapes are detected at driver intialization, the
+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