2.11BSD#431 - /usr/man/cat4/mtio.0

MTIO(4)             UNIX Programmer's Manual		  MTIO(4)


NAME
     mtio - UNIX magtape interface

DESCRIPTION
     The files mt0, ..., mt15 refer to the UNIX magtape drives,
     which may be on the MASSBUS using the TM03 formatter ht(4),
     or on the UNIBUS using either the TM11 or TS11 formatters
     tm(4) or ts(4).  The following description applies to any of
     the transport/controller pairs.

     The files mt0, ..., mt7 are 800bpi (or the transport's
     lowest density), mt8, ..., mt15 are 1600bpi (or the
     transport's second density), and mt16, ..., mt23 are 6250bpi
     (or the transport's third density).  (But note that only
     1600 bpi is available with the TS11.) The files mt0, ...,
     mt3, mt8, ..., mt11, and mt16, ..., mt19 are rewound when
     closed; the others are not.  When a file open for writing is
     closed, two end-of-files are written.  If the tape is not to
     be rewound it is positioned with the head between the two
     tapemarks.

     A standard tape consists of a series of 1024 byte records
     terminated by an end-of-file.  To the extent possible, the
     system makes it possible, if inefficient, to treat the tape
     like any other file.  Seeks have their usual meaning and it
     is possible to read or write a byte at a time.  Writing in
     very small units is inadvisable, however, because it uses
     most of the tape in record gaps.

     The mt files discussed above are useful when it is desired
     to access the tape in a way compatible with ordinary files.
     When foreign tapes are to be dealt with, and especially when
     long records are to be read or written, the `raw' interface
     is appropriate.  The associated files are named rmt0, ...,
     rmt23, but the same minor-device considerations as for the
     regular files still apply.  A number of other ioctl opera-
     tions are available on raw magnetic tape.	The following
     definitions are from <sys/mtio.h>:

     /*
      * Structures and definitions for mag tape io control commands
      */

     /* structure for MTIOCTOP - mag tape op command */
     struct    mtop {
	  short     mt_op;	   /* operations defined below */
	  daddr_t   mt_count; /* how many of them */
     };

     /* operations */
     #define MTWEOF 0	 /* write an end-of-file record */
     #define MTFSF  1	 /* forward space file */


Printed 11/26/99	December 22, 1995			1


MTIO(4)             UNIX Programmer's Manual		  MTIO(4)


     #define MTBSF  2	 /* backward space file */
     #define MTFSR  3	 /* forward space record */
     #define MTBSR  4	 /* backward space record */
     #define MTREW  5	 /* rewind */
     #define MTOFFL 6	 /* rewind and put the drive offline */
     #define MTNOP  7	 /* no operation, sets status only */
     #define MTCACHE	 8    /* enable controller cache */
     #define MTNOCACHE	 9    /* disable controller cache */

     /* structure for MTIOCGET - mag tape get status command */

     struct    mtget	 {
	  short     mt_type;  /* type of magtape device */
     /* the following two registers are grossly device dependent */
	  short     mt_dsreg; /* ``drive status'' register */
	  short     mt_erreg; /* ``error'' register */
     /* end device-dependent registers */
	  short     mt_resid; /* residual count */
     /* the following two are not yet implemented */
	  daddr_t   mt_fileno;	   /* file number of current position */
	  daddr_t   mt_blkno; /* block number of current position */
     /* end not yet implemented */
     };

     /*
      * Constants for mt_type byte.  These are the same
      * for other controllers compatible with the types listed.
      */
     #define   MT_ISTS	      0x01	/* TS-11 */
     #define   MT_ISHT	      0x02	/* TM03 Massbus: TE16, TU45, TU77 */
     #define   MT_ISTM	      0x03	/* TM11/TE10 Unibus */
     #define   MT_ISMT	      0x04	/* TM78/TU78 Massbus */
     #define   MT_ISUT	      0x05	/* SI TU-45 emulation on Unibus */
     #define   MT_ISCPC  0x06	   /* SUN */
     #define   MT_ISAR	      0x07	/* SUN */
     #define   MT_ISTMSCP     0x08	/* DEC TMSCP protocol (TU81, TK50) */

     /* mag tape io control commands */
     #define   MTIOCTOP  _IOW(m, 1, struct mtop)       /* do a mag tape op */
     #define   MTIOCGET  _IOR(m, 2, struct mtget) /* get tape status */
     #define MTIOCIEOT	 _IO(m, 3)	     /* ignore EOT error */
     #define MTIOCEEOT	 _IO(m, 4)	     /* enable EOT error */

     #ifndef KERNEL
     #define   DEFTAPE	 "/dev/rmt12"
     #endif

     Each read or write call reads or writes the next record on
     the tape.	In the write case the record has the same length
     as the buffer given.  During a read, the record size is
     passed back as the number of bytes read, provided it is no
     greater than the buffer size; if the record is long, an


Printed 11/26/99	December 22, 1995			2


MTIO(4)             UNIX Programmer's Manual		  MTIO(4)


     error is indicated.  In raw tape I/O seeks are ignored.  A
     zero byte count is returned when a tape mark is read, but
     another read will fetch the first record of the new tape
     file.

     The MTCACHE and MTNOCACHE commands do not apply to all tape
     drivers.  At present only the TMSCP driver supports those
     commands and then only for drives such as the TU81+.

FILES
     /dev/mt?
     /dev/rmt?

SEE ALSO
     mt(1), tar(1), tp(1), ht(4), tm(4), ts(4)

BUGS
     The status should be returned in a device independent for-
     mat.

     The special file naming should be redone in a more con-
     sistent and understandable manner.


Printed 11/26/99	December 22, 1995			3