mtio(7)                                                   mtio(7)



     NAME
          mtio - interface conventions for magnetic tape devices

     DESCRIPTION
          The mtio library allows applications to access tape  devices
          using a standard interface.

          While the general read, write, and seek operations are  part
          of  the  standard  I/O library, additional library resources
          are required to add support for tape devices.  The mtio  li-
          brary  helps provide a fairly device-independent way to per-
          form additional operations, such as rewind, that are  common
          to tape drives, but not common to other types of devices.

          There are several system-dependent parameters that this gen-
          eric  device  interface uses.  The most important is a stan-
          dard I/O block size,  BLKDEV_IOSIZE,  which  is  defined  in
          <sys/param.h>.   For A/UX, this value is 1024.  The commands
          that typically are used in conjunction with  a  tape  drive,
          such  as  tar(1),  ultimately  generate requests to read and
          write 1024-byte blocks when the tape devices  are  specified
          for  either  input or output.  However, a peculiarity of the
          Apple SC 40 Tape Backup is that it can only read  and  write
          in  blocks  of  8192 bytes, requiring a specially formulated
          user command line (see tc(7) and tcb(1)).

          The mtio library moderates device I/O when output is sent to
          or obtained from the device files in /dev/rmt.

     IOCTLS
          When manipulating the tape cartridge  device  more  directly
          through  your  own  programs,  or  through  programs such as
          mt(1), tape-specific operations are supported  through  mtio
          ioctls.  With a few exceptions, these generic operations are
          shared by all tape drives.  One exception is the  ``format''
          ioctl  (MTFORMAT),  which  is  available for the Apple SC 40
          Tape Backup only; in general, this is not a function of reel
          tape  drives, such as 9-track tape drives.  Other exceptions
          that apply to the  tape  cartridge  unit  are  described  in
          tc(7).   The  following  is a list of mtio ioctls, and their
          associated subcommands.  For complete details about the data
          structures, see <sys/mtio.h>.

          ioctl(fd, MTIOCGET, *mtget)
               This tape ioctl causes the  tape  unit  to  return  the
               status of the tape drive, returning values in mtget.

          ioctl(fd, MTIOCTOP, *mtop)
               This tape ioctl causes the tape unit to peform the sub-
               command  selected  by  the current values stored in the
               structure mtop.




     April, 1990                                                     1

     mtio(7)                                                   mtio(7)



               The subcommands for MTIOCTOP include:

              MTWEOF     write an end-of-file record

              MTFSF      forward space file

              MTBSF      backward space file

              MTFSR      forward space record

              MTBSR      backward space record

              MTREW      rewind

              MTOFFL     rewind and put the drive offline

              MTNOP      no operation, sets status only

     FILES
          /usr/lib/sys/ioctl.h
          /usr/lib/sys/mtio.h
          /dev/rmt/*

     SEE ALSO
          mt(1), tar(1), tcb(1), tp(1), tc(7).






























     2                                                     April, 1990