dsk(7)                     DG/UX 4.30                      dsk(7)



     NAME
          dsk - block special disk interface

     DESCRIPTION
          This block special device provides direct access to a
          logical or physical disk.  With respect to the I/O system
          calls, the disk may be considered to be the same as an
          ordinary disk file of size N*512 bytes, when N is the number
          of blocks in the disk.  The size is, however, only an
          attribute of the device; the file system considers all
          block-special devices to have size zero.

          The open system call performs device-specific operations to
          initialize the disk.  Except for errors that may be reported
          because of controller or unit failures, user visible
          functionality is the same as for an ordinary disk file.

          User visible functionality for the close system call is the
          same as for an ordinary disk file.

          The read system call may read any portion of the disk on any
          byte boundary for any number of bytes, without regard for
          disk block boundaries.  The file pointer associated with the
          descriptor used in the read system call is used to determine
          the location of the data to be read; hence the lseek system
          call works the same as for an ordinary disk file.  Reading
          data that has "never been written" returns whatever happens
          to be there, in contrast to an ordinary disk file which
          returns zeros.  A read request that extends past the end of
          the disk returns the error ENXIO and an implementation-
          specific amount of data.

          The write system call works in the same way as read, without
          regard for block boundaries.  Note that as for an ordinary
          disk file, the physical I/O to the physical disk is not
          guaranteed to have been completed when the write system call
          completes unless the OSYNC flag has been set on the file
          descriptor.  A write request that extends past the end of
          the disk returns the error ENXIO and writes an
          implementation-specific amount of data.

          The only disk specific ioctl is DSKIOCGET, which returns
          information about the characteristics of a disk.  The
          command and structure for this ioctl is defined in
          <sys/ioctl.h>.

          A pointer to the structure dskget is the parameter that is
          passed on the system call.

          struct    dskget
               {
               unsigned long  total_sectors;



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     dsk(7)                     DG/UX 4.30                      dsk(7)



               unsigned long  bytes_per_sector;
               unsigned short controller_id;
               };

          The total_sectors field is the number of 512 byte blocks
          available on the disk.   The blocks have addresses 0 through
          "total_sectors" - 1.  This value does not include blocks
          that are normally inaccessible because they are used for
          controller remapping, for diagnostic tracks, or for
          controller firmware.  Some of the blocks may not be useable
          because of media flaws.  The controller_id field is a
          controller-unique identifier reported by the disk
          controller.   A returned value of 0 indicates that the
          controller does not report an id.

          Select always returns READY for both read and write
          operations.

     FILES
          /dev/dsk/*               Logical disk device names for block
                                   special access

          /dev/pdsk/*              Physical disk device names for
                                   block special access

          /usr/include/sys/ioctl.h Ioctl definitions

     SEE ALSO
          cied(7), cimd(7), cird(7) ,sd(7), intro(7).


























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