accessing physical memory from linux kernel

Question

Can we access any physical memory via some kernel code.? Because, i wrote a device driver which only had init_module and exit_module.. the code is following.

int init_module(void) {
    unsigned char *p = (unsigned char*)(0x10);
    printk( KERN_INFO  "I got %u \n", *p);
    return 0;
}

and a dummy exit_module.. the problem is the computer gets hung when i do lsmod.. What happens? Should i get some kinda permission to access the mem location?

kindly explain.. I'm a beginner!

Answer 1

To access real physical memory you should use phys_to_virt function. In case it is io memory (e.g. PCI memory) you should have a closer look at ioremap.

This whole topic is very complex, if you are a beginner I would suggest some kernel/driver development books/doc.

Answer 2

I suggest reading the chapter about memory in this book:

http://lwn.net/Kernel/LDD3/

It's available online for free. Good stuff!