void *mmap(void *addr, size_t len, int prot, int flags, int fd, off_t offset);

unsigned long vm_start; /* Our start address within vm_mm. */
unsigned long vm_end; /* The first byte after our end address within vm_mm. */
unsigned long vm_flags; /* Flags, see mm.h. 该区域的标记。如VM_IO（该VMA标记为内存映射的IO区域,会阻止系统将该区域包含在进程的存放转存中）和VM_RESERVED（标志内存区域不能被换出）。*/

static int mmap(struct file *file, struct vm_area_struct *vma)；

int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr, unsigned long pfn, unsigned long size, pgprot_t prot)；
/**
* remap_pfn_range - remap kernel memory to userspace
* @vma: user vma to map to：内核找到的虚拟地址区间
* @addr: target user address to start at：要关联的虚拟地址
* @pfn: physical address of kernel memory：要关联的设备的物理地址，也即要映射的物理地址所在的物理帧号，可将物理地址>>PAGE_SHIFT
* @size: size of map area
* @prot: page protection flags for this mapping
*
* Note: this is only safe if the mm semaphore is held when called.
*/

#ifndef _MEMDEV_H_
#define _MEMDEV_H_#ifndef MEMDEV_MAJOR
#define MEMDEV_MAJOR 0   /*预设的mem的主设备号*/
#endif#ifndef MEMDEV_NR_DEVS
#define MEMDEV_NR_DEVS 2    /*设备数*/
#endif#ifndef MEMDEV_SIZE
#define MEMDEV_SIZE 4096
#endif

/*mem设备描述结构体*/
struct mem_dev
{                                                        char *data;                      unsigned long size;
};#endif /* _MEMDEV_H_ */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>#include <linux/kernel.h>
#include "memdev.h"

static int mem_major = MEMDEV_MAJOR;module_param(mem_major, int, S_IRUGO);struct mem_dev *mem_devp; /*设备结构体指针*/struct cdev cdev; /*文件打开函数*/
int mem_open(struct inode *inode, struct file *filp)
{struct mem_dev *dev;/*获取次设备号*/int num = MINOR(inode->i_rdev);if (num >= MEMDEV_NR_DEVS) return -ENODEV;dev = &mem_devp[num];/*将设备描述结构指针赋值给文件私有数据指针*/filp->private_data = dev;return 0;
}/*文件释放函数*/
int mem_release(struct inode *inode, struct file *filp)
{return 0;
}
static int memdev_mmap(struct file*filp, struct vm_area_struct *vma)
{struct mem_dev *dev = filp->private_data; /*获得设备结构体指针*/vma->vm_flags |= VM_IO;vma->vm_flags |= VM_RESERVED;if (remap_pfn_range(vma,vma->vm_start,virt_to_phys(dev->data)>>PAGE_SHIFT, vma->vm_end - vma->vm_start, vma->vm_page_prot))return  -EAGAIN;return 0;
}/*文件操作结构体*/
static const struct file_operations mem_fops =
{.owner = THIS_MODULE,.open = mem_open,.release = mem_release,.mmap = memdev_mmap,
};/*设备驱动模块加载函数*/
static int memdev_init(void)
{int result;int i;dev_t devno = MKDEV(mem_major, 0);/* 静态申请设备号*/if (mem_major)result = register_chrdev_region(devno, 2, "memdev");else  /* 动态分配设备号 */{result = alloc_chrdev_region(&devno, 0, 2, "memdev");mem_major = MAJOR(devno);}  if (result < 0)return result;/*初始化cdev结构*/cdev_init(&cdev, &mem_fops);cdev.owner = THIS_MODULE;cdev.ops = &mem_fops;/* 注册字符设备 */cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);/* 为设备描述结构分配内存*/mem_devp = kmalloc(MEMDEV_NR_DEVS * sizeof(struct mem_dev), GFP_KERNEL);if (!mem_devp)    /*申请失败*/{result =  - ENOMEM;goto fail_malloc;}memset(mem_devp, 0, sizeof(struct mem_dev));/*为设备分配内存*/for (i=0; i < MEMDEV_NR_DEVS; i++) {mem_devp[i].size = MEMDEV_SIZE;mem_devp[i].data = kmalloc(MEMDEV_SIZE, GFP_KERNEL);memset(mem_devp[i].data, 0, MEMDEV_SIZE);}return 0;fail_malloc: unregister_chrdev_region(devno, 1);return result;
}/*模块卸载函数*/
static void memdev_exit(void)
{cdev_del(&cdev);   /*注销设备*/kfree(mem_devp);     /*释放设备结构体内存*/unregister_chrdev_region(MKDEV(mem_major, 0), 2); /*释放设备号*/
}MODULE_AUTHOR("David Xie");
MODULE_LICENSE("GPL");module_init(memdev_init);
module_exit(memdev_exit);

#include <stdio.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>
#include<sys/mman.h>int main()
{int fd;char *start;//char buf[100];
    char *buf;/*打开文件*/fd = open("/dev/memdev0",O_RDWR);buf = (char *)malloc(100);memset(buf, 0, 100);start=mmap(NULL,100,PROT_READ|PROT_WRITE,MAP_SHARED,fd,0);/* 读出数据 */strcpy(buf,start);sleep (1);printf("buf 1 = %s\n",buf);    /* 写入数据 */strcpy(start,"Buf Is Not Null!");memset(buf, 0, 100);strcpy(buf,start);sleep (1);printf("buf 2 = %s\n",buf);munmap(start,100); /*解除映射*/free(buf);close(fd);  return 0;
}