System Software

System Software

For kernel-level device drivers, all 4.x and later versions of the IRIX operating system provide a consistent, device-independent interface that allows the user to treat a device as a file to be opened, read, written, and closed. These calls serve as the interface between the user and the device (see Figure 1-6). This means that, for most I/O operations, you need not provide the user with device-specific system calls. Instead, the user can use the standard system call, open(), to get a file descriptor for the device, then read, write, and close the "file" pointed to by the file descriptor. Internally, the system calls use the driver module that you have written to handle the device.

Figure 1-6 : Device Driver Position in the Kernel