rdsk(7)                          DG/UX 5.4.2                         rdsk(7)


NAME
       rdsk - character special disk interface

DESCRIPTION
       This character special device provides direct access to a logical or
       physical disk in a slightly different manner from dsk(7).  In this
       case, the disk should be considered to be an array of 512-byte disk
       blocks numbered from 0 to N-1, where N is the number of blocks in the
       disk.

       The rdsk device is typically implemented so that requests for large
       amounts of data (say, an entire track of the disk) can be serviced
       with far fewer explicit requests to the physical disk than can the
       dsk device.  Efficiency  improves because of restrictions in the way
       rdsk may be used, as described below.

       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.

       For the close system call, user-visible functionality is the same as
       for an ordinary disk file.

       The read system call must begin and end on a 512-byte boundary; i.e.,
       the starting address and the length of the read must be multiples of
       512.  Reads on other boundaries and of other sizes will return the
       error EINVAL.  Reading data that has "never been written" returns
       whatever happens to be there, in contrast to an ordinary disk file
       which returns zero.  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 must begin and end on a 512-byte boundary;
       i.e., the starting address and the length of the write must be
       multiples of 512.  Write on other boundaries and of other sizes will
       return the error EINVAL.  Also, the data is guaranteed to have been
       physically written to the disk upon completion of the write system
       call.  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  totalsectors;
            unsigned short bytespersector;
            unsigned short controllerid;
            };



Licensed material--property of copyright holder(s)                         1

rdsk(7)                          DG/UX 5.4.2                         rdsk(7)


       The total_sectors field is the number of sectors available on the
       disk.   The sectors have addresses 0 through "total_sectors" - 1.
       This value does not include sectors that are normally inaccessible
       because they are used for controller remapping, for diagnostic
       tracks, or for controller firmware.  Some of the sector blocks may be
       not be useable because of media flaws.  The bytes_per_sector field
       indicates the size, in bytes, of each sector.  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/rdsk/*              Logical disk device names for character
                                special access
       /dev/rpdsk/*             Physical disk device names for character
                                special access
       /usr/include/sys/ioctl.h Ioctl definitions

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



































Licensed material--property of copyright holder(s)                         2