Very Computer

by Le » Fri, 30 May 2003 22:00:22

I have a newbie question on device driver. Although I have finished a
simple dummy device driver, I am still puzzled. The user program
using driver API are executed in user space with CPU CPL=3, and I
suppose the driver itself should be running with CPU CPL=0, privilege
mode, actually it should not have inaccessible resources. Then how
the switch happens? To enter system call to change CPU cpl=0, we can
use int 0x80. What about from user to drive code?

Thanks.

Lee

by **Catalin Marina** » Sat, 31 May 2003 01:12:53

> I have a newbie question on device driver. Although I have finished a
> simple dummy device driver, I am still puzzled. The user program
> using driver API are executed in user space with CPU CPL=3, and I
> suppose the driver itself should be running with CPU CPL=0, privilege
> mode, actually it should not have inaccessible resources. Then how
> the switch happens? To enter system call to change CPU cpl=0, we can
> use int 0x80. What about from user to drive code?

You access the driver API using system calls. For example, you call
open() from the C library which calls the sys_open() system call
(through an "int 0x80", CPL becomes 0) which calls the dev_open()
function in your driver.

Catalin

Very Computer

device drive running in priviledged mode?

device drive running in priviledged mode?

device drive running in priviledged mode?