#include <linux/init.h> #include <linux/module.h> #include <linux/types.h> #include <linux/mm.h> #include <linux/fs.h> #include <linux/errno.h> #include <linux/sched.h> #include <linux/cdev.h> #include <asm/io.h> //#include <asm/system.h> //找不到这个文件 #include <linux/slab.h> // for kmalloc and kfree function #include <asm/uaccess.h> #define GLOBALMEM_SIZE 0X1000 /*全局内存最大4KB*/ #define MEM_CLEAR 0x1 /*清零全局内存*/ #define GLOBALMEM_MAJOR 354 static int globalmem_major = GLOBALMEM_MAJOR;/*预设的globalmem的主设备号*/ /*globalmem的设备结构体:包含了对应于globalmem字符设备的cdev 和 使用内存mem[GLOBALMEM_SIZE]*/ struct globalmem_dev { struct cdev cdev; //cdev结构体 unsigned char mem[GLOBALMEM_SIZE]; //全局内存 }; struct globalmem_dev *globalmem_devp; //设备结构体指针 /*文件打开函数*/ int globalmem_open(struct inode *inode,struct file *filp) { filp->private_data = globalmem_devp; //将设备结构体指针赋值给文件私有数据指针 return 0; } /*文件释放函数*/ int globalmem_release(struct inode *inode,struct file *filp) { return 0; } /*设备控制函数:ioctl()函数接受的MEM_CLEAR命令,这个命令将全局内存的有效数据长度清零,对于设备不支持的命令,ioctl()函数应该返回-EINVAL*/ static long globalmem_ioctl( /*struct inode *inodep,*/struct file *filp,unsigned int cmd,unsigned long arg) { struct globalmem_dev *dev = filp->private_data; //获得设备结构体指针 switch(cmd) { case MEM_CLEAR: memset(dev->mem,0,GLOBALMEM_SIZE); printk(KERN_INFO"globalmem is set to zero\n"); break; default: return -EINVAL; } return 0; } /*读函数:读写函数主要是让设备结构体的mem[]数组与用户空间交互数据,并随着访问字节数变更返回用户的文件读写偏移位置*/ static ssize_t globalmem_read(struct file *filp,char __user *buf,size_t size,loff_t *ppos ) { unsigned long p = *ppos; unsigned int count = size; int ret = 0; struct globalmem_dev *dev = filp->private_data; //获得设备结构体指针 if(p >= GLOBALMEM_SIZE) //分析和获取有效的写长度 { return count ? -ENXIO:0; } if(count > GLOBALMEM_SIZE - p) { count = GLOBALMEM_SIZE - p; } if(copy_to_user(buf,(void *)(dev->mem+p),count)) //内核空间->用户空间 { ret = -EFAULT; } else { *ppos += count; ret = count; printk(KERN_INFO"read %d bytes(s) from %ld\n",count,p); } return ret; } /*写函数*/ static ssize_t globalmem_write(struct file *filp,const char __user *buf,size_t size,loff_t *ppos) { unsigned long p = *ppos; unsigned int count = size; int ret = 0; struct globalmem_dev *dev = filp->private_data; if(p >= GLOBALMEM_SIZE) //分析和获取有效的写长度 { return count? -ENXIO:0; } if(count > GLOBALMEM_SIZE - p) { count = GLOBALMEM_SIZE - p; } if(copy_from_user(dev->mem + p,buf,count)) // 用户空间->内核空间 { ret = -EFAULT; } else { *ppos =+ count; ret = count; printk(KERN_INFO"written %d bytes(s) from %ld\n",count,p); } return ret; } /*seek文件定位函数:seek()函数对文件定位的起始地址可以是文件开头(SEEK_SET,0)、当前位置(SEEK_CUR,1)、文件尾(SEEK_END,2)*/ static loff_t globalmem_llseek(struct file *filp,loff_t offset,int orig) { loff_t ret = 0; switch(orig) { case 0: //相对文件开始位置偏移 if(offset <0 ) { ret = -EINVAL; break; } if((unsigned int )offset > GLOBALMEM_SIZE) { ret = - EINVAL; break; } filp->f_pos = (unsigned int)offset; ret = filp->f_pos; break; case 1: //相对文件当前位置偏移 if((filp->f_pos + offset) > GLOBALMEM_SIZE) { ret = -EINVAL; break; } if((filp->f_pos + offset)<0) { ret = -EINVAL; break; } filp->f_pos +=offset; ret = filp->f_pos; break; default: ret = -EINVAL; break; } return ret; } /*文件操作结构体*/ static const struct file_operations globalmem_fops= { .owner = THIS_MODULE, .llseek = globalmem_llseek, .read = globalmem_read, .write = globalmem_write, // .ioctl = globalmem_ioctl, .unlocked_ioctl = globalmem_ioctl, .open = globalmem_open, .release = globalmem_release, }; /*初始化并注册cdev*/ static void globalmem_setup_cdev(struct globalmem_dev *dev,int index) { int err,devno = MKDEV(globalmem_major,index); cdev_init(&dev->cdev,&globalmem_fops); dev->cdev.owner = THIS_MODULE; dev->cdev.ops = &globalmem_fops; err = cdev_add(&dev->cdev,devno,1); if(err) { printk(KERN_NOTICE"Error %d adding LED%d",err,index); } } /*设备驱动模块加载函数*/ static int __init globalmem_init(void) { int result; dev_t devno = MKDEV(globalmem_major,0); if(globalmem_major) //申请设备号 { result = register_chrdev_region(devno,1,"globalmem"); } else //动态申请设备号 { result = alloc_chrdev_region(&devno,0,1,"globalmem"); globalmem_major = MAJOR(devno); } if(result < 0) { return result; } globalmem_devp = kmalloc(sizeof(struct globalmem_dev),GFP_KERNEL); //申请设备结构体的内存 if(!globalmem_devp) { result = -ENOMEM; goto fail_malloc; } memset(globalmem_devp,0,sizeof(struct globalmem_dev)); globalmem_setup_cdev(globalmem_devp,0); return 0; fail_malloc:unregister_chrdev_region(devno,1); return result; } /*模块卸载函数*/ static void __exit globalmem_exit(void) { cdev_del(&globalmem_devp->cdev); //注销cdev kfree(globalmem_devp); //释放设备结构体内存 unregister_chrdev_region(MKDEV(globalmem_major,0),1); //释放设备号 } MODULE_AUTHOR("Song Baohua"); MODULE_LICENSE("Dual BSD/GPL"); module_param(globalmem_major,int,S_IRUGO); module_init(globalmem_init); module_exit(globalmem_exit);
2. Makefile:
</pre><p></p><pre name="code" class="plain">KERNELDIR := /lib/modules/$(shell uname -r)/build obj-m := globalmem.o modules: $(MAKE) -C $(KERNELDIR) M=$(PWD) modules modules_install: $(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install clean: make -C $(KERNELDIR) M=`pwd` modules clean rm -rf modules.order
4.
验证:lsmod 可以看到该模块,mknod /dev/globalmem c 354 0, echo 'good nihao' > /dev/globalmem, cat /dev/globalmem可以看到输出good nihao;
还出现了:cat: /dev/globalmem: 没有那个设备或地址,目前不知道是什么问题;
代码验证:
#include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> void main(void) { int fd; int i; char data[256]; int retval; fd = open("/dev/globalmem",O_RDWR); if(fd==-1) { perror("erroropen\n"); exit(-1); } printf("open/dev/globalmem successfully\n"); //写数据 retval = write(fd,"mem",3); if(retval==-1) { perror("writeerror\n"); exit(-1); } printf("write successfully\n"); close(fd); //若不重新打开,则globalmem.c中的write函数写入后,其写位置*ppos更新了,所以导致下面的读将从写入后的位置 // 开始读,从而导致读不到数据,如写入后,*ppos位置为9,下次读时将从位置9开始读,导致读不到数据,当然可以设置为
// 从文件开始位置读,如:copy_to_user(buf, dev->mem, count) fd = open("/dev/globalmem",O_RDWR); // 重新打开后,globalmem.c中的read和write函数中的读写位置都是为0 if(fd==-1) // <span style="color:#ff0000;">上面不关闭也行,使用lseek( fd, 0L, SEEK_SET );就可以了</span> { perror("erroropen\n"); exit(-1); } //读数据 retval=read(fd,data,3 ); if(retval==-1) { perror("readerror\n"); exit(-1); } data[retval]=0; printf("read successfully:%s\n",data); //关闭设备 close(fd); }输出如下:
open/dev/globalmem successfully
write successfully
read successfully:mem