Linux using a driver from inside a driver

Question

I am trying to interface to a microcontroller from my linux box via RS232 serial.

I have written the driver and implemented a protocol b/n pc and microcontroller, which uses a tty(/dev/ttyS0) device already present in the kernel as a module(eg via calling open, close, etc..). However, when I try to compile, it says it cannot find reference to open, write, read etc...

How do I just use an existing device driver from within a driver? Is there something else I need to include?

If not, how can I use the serial port easily from within a driver?

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/cdev.h>
#include <linux/spinlock.h>
#include <linux/termios.h>
#include <linux/fcntl.h>
#include <linux/unistd.h>

MarkR MarkR · Accepted Answer · 2011-05-09T06:37:06

Normally you should do such a thing in userspace - implement your device's protocol in a normal, userspace program.

It is possible, but definitely not recommended to do these things in the kernel. For example, the ppp driver implements a network driver on top of a serial driver. I don't know how it works in that case, but I'd expect that a userspace helper program opens the device, initialises its parameters etc, then passes the file descriptor into the kernel using some system call.

You cannot call arbitrary library functions from the kernel - or indeed, any library functions at all (except libraries which are actually shipped as part of the kernel). This includes kernel system calls. There are equivalent functions which it may be possible to call - for example, filp_open.

In most cases you can't just call the normal syscall from the kernel, as they expect pointers to point to userspace data, but in the kernel yours (allocated via kalloc etc) will normally point to kernel-space data. The two can't be freely mixed.

Linux using a driver from inside a driver

1 Answers