#include <linux/module.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>
#include <asm/pgtable.h>
#include <linux/mm.h>
#include <linux/slab.h>

/* 1. 确定主设备号                                                                 */
static int major = 0;
static char *kernel_buf;
static struct class *hello_class;
static int bufsiz = 1024*8;

#define MIN(a, b) (a < b ? a : b)

/* 3. 实现对应的open/read/write等函数，填入file_operations结构体                   */
static ssize_t hello_drv_read (struct file *file, char __user *buf, size_t size, loff_t *offset)
{
	int err;
	printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
	err = copy_to_user(buf, kernel_buf, MIN(bufsiz, size));
	return MIN(bufsiz, size);
}

static ssize_t hello_drv_write (struct file *file, const char __user *buf, size_t size, loff_t *offset)
{
	int err;
	printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
	err = copy_from_user(kernel_buf, buf, MIN(1024, size));
	return MIN(1024, size);
}

static int hello_drv_mmap(struct file *file, struct vm_area_struct *vma)
{
	/* 获得物理地址 */
	unsigned long phy = virt_to_phys(kernel_buf);

	/* 设置属性: cache, buffer */
	vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);

	/* map */
	if (remap_pfn_range(vma, vma->vm_start, phy >> PAGE_SHIFT,
			    vma->vm_end - vma->vm_start, vma->vm_page_prot)) {
		printk("mmap remap_pfn_range failed\n");
		return -ENOBUFS;
	}

	return 0;
}

static int hello_drv_open (struct inode *node, struct file *file)
{
	printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
	return 0;
}

static int hello_drv_close (struct inode *node, struct file *file)
{
	printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
	return 0;
}

/* 2. 定义自己的file_operations结构体                                              */
static struct file_operations hello_drv = {
	.owner	 = THIS_MODULE,
	.open    = hello_drv_open,
	.read    = hello_drv_read,
	.write   = hello_drv_write,
	.release = hello_drv_close,
	.mmap    = hello_drv_mmap,
};

static int __init hello_init(void)
{
	int err;

	kernel_buf = kmalloc(bufsiz, GFP_KERNEL);
	strcpy(kernel_buf, "old");
	
	printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
	major = register_chrdev(0, "hello", &hello_drv);  /* /dev/hello */

	hello_class = class_create(THIS_MODULE, "hello_class");
	err = PTR_ERR(hello_class);
	if (IS_ERR(hello_class)) {
		printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
		unregister_chrdev(major, "hello");
		return -1;
	}
	
	device_create(hello_class, NULL, MKDEV(major, 0), NULL, "hello"); /* /dev/hello */
	
	return 0;
}

static void __exit hello_exit(void)
{
	printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
	device_destroy(hello_class, MKDEV(major, 0));
	class_destroy(hello_class);
	unregister_chrdev(major, "hello");
	kfree(kernel_buf);
}
module_init(hello_init);
module_exit(hello_exit);
MODULE_LICENSE("GPL");

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>

/*
 * ./hello_drv_test
 */
int main(int argc, char **argv)
{
	int fd;
	char *buf;
	int len;
	char str[1024];
	
	
	/* 1. 打开文件 */
	fd = open("/dev/hello", O_RDWR);
	if (fd == -1)
	{
		printf("can not open file /dev/hello\n");
		return -1;
	}

	/* 2. mmap 
	 * MAP_SHARED  : 多个APP都调用mmap映射同一块内存时, 对内存的修改大家都可以看到。
	 *               就是说多个APP、驱动程序实际上访问的都是同一块内存
	 * MAP_PRIVATE : 创建一个copy on write的私有映射。
	 *               当APP对该内存进行修改时，其他程序是看不到这些修改的。
	 *               就是当APP写内存时, 内核会先创建一个拷贝给这个APP, 
	 *               这个拷贝是这个APP私有的, 其他APP、驱动无法访问。
	 */
	buf =  mmap(NULL, 1024*8, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
	if (buf == MAP_FAILED)
	{
		printf("can not mmap file /dev/hello\n");
		return -1;
	}

	printf("mmap address = 0x%x\n", buf);
	printf("buf origin data = %s\n", buf); /* old */

	/* 3. write */
	strcpy(buf, "new");

	/* 4. read & compare */
	/* 对于MAP_SHARED映射:  str = "new" 
	 * 对于MAP_PRIVATE映射: str = "old" 
	 */
	read(fd, str, 1024);  
	if (strcmp(buf, str) == 0)
	{
		/* 对于MAP_SHARED映射，APP写的数据驱动可见
		 * APP和驱动访问的是同一个内存块
		 */
		printf("compare ok!\n");
	}
	else
	{
		/* 对于MAP_PRIVATE映射，APP写数据时, 是写入原来内存块的"拷贝"
		 */
		printf("compare err!\n");
		printf("str = %s!\n", str);  /* old */
		printf("buf = %s!\n", buf);  /* new */
	}

	while (1)
	{
		sleep(10);  /* cat /proc/pid/maps */
	}
	
	munmap(buf, 1024*8);
	close(fd);
	
	return 0;
}