fd

Purpose

     Supports the diskette device driver.

Synopsis

     #include <sys/devinfo.h>

Description

     The diskette  special file  provides block  and character
     (raw)  access  to  diskettes   in  the  diskette  drives,
     allowing only one  process to have a  diskette drive open
     for writing at a time.   The config device driver associ-
     ates the  minor device number with  a particular diskette
     drive.  Normally, the special  file /dev/fdn is given the
     minor device  number n.   Removing the diskette  from the
     drive with  diskette files  still open may  cause various
     I/O system calls to return errors.

     The minor  device number specifies both  the drive number
     and the  format of  the diskette to  be read  or written.
     Assume that /dev/fdn corresponds to a diskette drive with
     minor device number n.  In  this case, fd0, fd1, fd2, and
     fd3 specify  diskette drives  0 through  3, respectively,
     without specifying their format.

     Using fs0, . . . ,  fs3, which correspond to minor device
     numbers 4 through 7, forces a diskette to be treated as a
     single-sided diskette.  Similarly, fd0.8,  . . . , fd3.8,
     which correspond  to minor  device numbers 8  through 11,
     force  the  diskette  to  be  treated  as  an  8-sectored
     diskette.   fs0.8, .  . .  , fs3.8,  which correspond  to
     minor device numbers 12 through 15, force the diskette to
     be treated as single-sided and 8-sectored.

     Configuration Data

     The config device driver is called during system initial-
     ization to customize diskettes.   This is accomplished by
     calling the  device driver  at its  initialization entry.
     For   diskettes,  no   device-dependent  information   is
     required, so  the customize information is  the following
     structure:

          struct {
              dev_t  devno;           /* major/minor device number */
              unsigned short  iodn;   /* IODN to set */
              unsigned short  ddilen; /* device dependent info length */
              unsigned short  lev;    /* ignored */
              union  {                /* optional device dependent info */
                     char ddi_fd[];

                      . . .            /* ddi for other devices */
              } ddi;
          };

     ioctl Operations

     The  IOCTYPE type  ioctl system  call returns  the device
     type DD_DISK, defined in the sys/devinfo.h header file.

     The IOCINFO type ioctl  system call returns the following
     structure, defined in the sys/devinfo.h header file:

          struct devinfo {
              char  devtype;
              char  flags;
              union {
                 struct {            /* for disks */
                    short  bytpsec;  /* bytes per sector */
                    short  secptrk;  /* sectors per track */
                    short  trkpcyl;  /* tracks per cylinder */
                    long   numblks;  /* number of blocks on diskette */
                 } dk;
                  . . .               /* for other devices */
              } un;
          };

          /* flags */
         #define DF_FIXED 01  /* non-removable */
         #define DF_RAND 02   /* random access possible */
         #define DF_FAST 04   /* a relative term */

Files

     /dev/fd0, /dev/fd1,  . . .
     /dev/rfd0, /dev/rfd1,  . . .

Related Information

     In this book:  "config,"  "fs," and  "ioctl."