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Show Physical Memory Address of the kernel module

Introduction

我希望透過寫一個kernel module，做以下事情:

  1. 宣告一個global variable。
  2. init時，初始此variable。
  3. 執行file_operations: open時，會打印出此變數的實體記憶體位置。
  4. exit時，釋放此variable。

How to?

#
## Makefile for kernel test
#
#PWD         := $(shell pwd) 
KVERSION    := $(shell uname -r)
KERNEL_DIR   = /usr/src/kernels/$(KVERSION)/
MODULE_NAME  = hello
obj-m       := $(MODULE_NAME).o   
all:
	make -C $(KERNEL_DIR) M=$(PWD) modules
clean:
	make -C $(KERNEL_DIR) M=$(PWD) clean

#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <asm/io.h>
#include <linux/fs.h>
 
MODULE_LICENSE("Dual BSD/GPL");
 
static char* hello_buf;
 
static int dump_physical_address(struct file *filp, struct vm_area_struct *vma)
{	
	unsigned long virt_addr;
	phys_addr_t phy_addr;
	printk("damn\n");	
	virt_addr = (unsigned long)hello_buf;
	printk("Hello kernel: %lx, value: %c\n", virt_addr, hello_buf[0]);
	phy_addr = virt_to_phys((void*)virt_addr);
	printk("PA: 0x%lx\n", phy_addr);
	pr_info("PA: %pa for VA: 0x%lx\n", &phy_addr, virt_addr);
	return 0;
}
 
static struct file_operations hello_fops = {
	open: 	dump_physical_address,	
}; 
 
static int hello_init(void)
{	
 
	int ret = register_chrdev(187, "hello", &hello_fops);
	if(ret<0) {
		printk("Unsable to register char device %d\n", ret);
		return ret;
	}
 
	hello_buf = kmalloc(256, GFP_KERNEL);
	memset(hello_buf,'*',256);
	printk("Hello kernel: %c\n", hello_buf[0]);
	return 0;
}
static void hello_exit(void)
{
	if(hello_buf) {
	  printk("Goodbyte kernel: %c\n", hello_buf[0]);
	  kfree(hello_buf);
	}
	unregister_chrdev(187,"hello");
	printk(KERN_INFO "Goodbye\n");
}
 
module_init(hello_init);
module_exit(hello_exit);

#!/bin/bash
 
#mknod /dev/hello c 187 0
 
rmmod hello
insmod hello.ko
cat /dev/hello
dmesg | tail

Reference