Device driver overview

Header files and declarations

The first lines in every DDI 8 driver source file must be:

   #define _KERNEL
   #define _DDI=8

The _DDI line gives the ``major'' version number, such as 7 or 8; it does not use full version numbers such as 8.1 or 8mp. These definitions can instead be given as arguments to the -D option of the cc line to compile the driver. For example, if the driver uses DDI 8 or DDI 8mp, the compile line would be:

   cc -D_KERNEL -D_DDI=8

The _DDI=8 definition is optional for DDI versions prior to version 8 and not supported for SCO OpenServer 5 drivers.

After these declarations, the source file has a list of #include lines that reference the header files (see ``Header files'') that are required by the driver at compile time. For example:

   1  #include <sys/types.h>
   2  #include "mydriv.h"
   3  #include <sys/ddi.h>

Lines 1 and 3 reference standard system header files, using a relative path to the header file directory, usually /usr/include. Line 2 declares a driver-specific header file that is located in the same directory as the rest of the driver source code. Driver-specific header files are typically #included after most system header files, but before the sys/ddi.h and related header files.

Driver-specific header files are coded as standard C language files. They contain global definitions and declarations, especially those that may also be accessed by user-level code, other driver code, and administrative tasks, including:

definitions for all driver-specific ioctl commands that are coded for the driver; see ioctl(D2) and M_IOCTL(D7str).
declarations of driver-specific structures.
flags and other defined constants for the driver.

In addition, drivers must make other declarations outside the entry point routines:

DDI 8 drivers must populate a drvinfo(D4) structure with information about the driver.
Drivers that use DDI versions prior to version 8 must declare the devflag(D1) integer variable.
STREAMS drivers and modules, including MDI drivers, must define an info variable with streamtab(D4str) information.