devinfo

Purpose

     Contains device characteristics.

Synopsis

     #include <sys/devinfo.h>

Description

     The devinfo  structure is  defined for each  device.  The
     IOCINFO operation of the ioctl  system call fills in this
     structure.  The information returned  by a device varies.
     Most devices,  other than disk devices,  return a devtype
     value and the remainder of this structure contains zeros.
     This structure  provides information about  the capabili-
     ties of a device, rather  than its current status or set-
     tings.  For  example, types  of information  provided are
     the number  of characters a  printer handles per  line or
     the diskette capacity in number of blocks.

     The maximum size of this structure is 12 bytes (no longer
     than  the disk  version), so  that programs  can use  the
     ioctl  system  call without  concern  of  overrun due  to
     increasing size.

          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;  /* blocks this minidisk */
                } dk;
                struct              /* for memory mapped displays */
                {
                   char  capab;     /* capabilities */
                   char  mode;      /* current mode */
                   short  hres;     /* horizontal resolution */
                   short  vres;     /* vertical resolution */
                } tt;
             } un;
           };

     The  following flags  specify  some generic  capabilities
     (see DD_DISK):

                    Constant  Value  Function
                    DF_FIXED  01     Not removable
                    DF_RAND   02     Random access possible
                    DF_FAST   04     A relative term

The devinfo  structures are defined  for the following devices  (specified in
the devtype field):

DD_DISK   Indicates a  disk.  This devtype  is R.  The driver  determines the
          values.  The  fixed disk  has flags DF_RAND  | DF_FIXED  | DF_FAST,
          while the diskette has flags DF_RAND (see "fd" and "hd").

          The number of  the bytes per sector, sectors per  track, and tracks
          per cylinder  for the fixed  disk are predetermined.   The minidisk
          table determines the number of blocks.  For the diskette, the minor
          device  driver or  the physical  media determines  this information
          when the device is opened.

DD_LP     Indicates a  line printer.  The  devtype is  l.  This fills  in the
          devtype field and returns zeros for the rest of the structure.

DD_PSEU   Indicates a pseudo-device.  This devtype is Z.

DD_RTC    Indicates a real-time (calendar) clock.  This devtype is c.

DD_TAPE   Indicates a magnetic tape.  This devtype is M.

DD_TTY    Indicates a  terminal.  This returns a  devtype of T and  zeros for
          the rest of the structure.

DT_STREAM Indicates a streaming tape drive.  The devtype is 2.

DT_STRTSTP Indicates a start-stop tape drive.  The devtype is 2.

Related Information

In this book:  "ioctl," "fd," and  "hd."