4.3BSD - /usr/man/cat4/mtio.0

MTIO(4)                                                                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  TM78  formatter,
       mt(4), or on the UNIBUS using either the TM11 or TS11 formatters tm(4),
       TU45 compatible formatters, ut(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 operations
       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 */
       #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  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.

FILES
       /dev/mt?
       /dev/rmt?

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

BUGS
       The status should be returned in a device independent format.

       The  special  file  naming  should  be  redone in a more consistent and
       understandable manner.


4.2 Berkeley Distribution        May 16, 1986                          MTIO(4)