记录一下 建立一个简单的字符设备的编码过程
前提准备:已经编译好的Linux内核
进入../drivers/char/目录
这里存放着这字符设备驱动
mkdir globalmem 创建一个我们新建驱动的目录并进入
新建globalmem.c文件,清单如下
#include <linux/module.h> #include <linux/fs.h> #include <linux/init.h> #include <linux/cdev.h> #include <linux/slab.h> #include <linux/uaccess.h> #define GLOBALMEM_SIZE 0x1000 #define MEM_CLEAR 0x1 #define GLOBALMEM_MAJOR 230 static int globalmem_major=GLOBALMEM_MAJOR; module_param(globalmem_major,int,S_IRUGO); struct globalmem_dev { struct cdev cdev; unsigned char mem[GLOBALMEM_SIZE]; }; struct globalmem_dev *globalmem_devp; static int globalmem_open(struct inode *inode,struct file *filep) { filep->private_data = globalmem_devp; return 0; } static int globalmem_release(struct inode *inode,struct file *filep) { return 0; } static long globalmem_ioctl(struct file *filep,unsigned int cmd,unsigned long arg) { struct globalmem_dev *dev = filep->private_data; 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; } static ssize_t globalmem_read(struct file *filep,char __user * buf,size_t size,loff_t * ppos) { unsigned long p = *ppos; unsigned int count=size; int ret = 0; struct globalmem_dev *dev = filep->private_data; if (p >=GLOBALMEM_SIZE) { return 0; } if(count>GLOBALMEM_SIZE-p) { count=GLOBALMEM_SIZE-p; } if(copy_to_user(buf,dev->mem+p,count)) { ret=-EINVAL; }else{ *ppos+=count; ret=count; printk(KERN_INFO "read %u bytes from %u\n",count,p); } return ret; } 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) return 0; if (count > GLOBALMEM_SIZE - p) count = GLOBALMEM_SIZE - p; if (copy_from_user(dev->mem + p, buf, count)) ret = -EFAULT; else { *ppos += count; ret = count; printk(KERN_INFO "written %u bytes(s) from %lu\n", count, p); } return ret; } static loff_t globalmem_llseek(struct file *filp, loff_t offset, int orig) { loff_t ret = 0; switch (orig) { case 0: 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: 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; } static const struct file_operations globalmem_fops = { .owner = THIS_MODULE, .llseek = globalmem_llseek, .read = globalmem_read, .write = globalmem_write, .unlocked_ioctl =globalmem_ioctl, .open = globalmem_open, .release = globalmem_release, }; static void globalmem_setup_cdev(struct globalmem_dev *dev,int index) { int err,devno = MKDEV(globalmem_major,index);//定义设备编号 cdev_init(&dev->cdev,&globalmem_fops); dev->cdev.owner = THIS_MODULE; err = cdev_add(&dev->cdev,devno,1); if(err) printk(KERN_NOTICE "Error %d adding globalmem%d",err,index); } static int __init globalmem_init(void) { int ret; dev_t devno =MKDEV(globalmem_major,0); if(globalmem_major) ret = register_chrdev_region(devno,1,"globalmem"); else{ ret = alloc_chrdev_region(&devno,0,1,"globalmem"); globalmem_major=MAJOR(devno); } if(ret<0) return ret; globalmem_devp = kzalloc(sizeof(struct globalmem_dev),GFP_KERNEL); if(!globalmem_devp){ ret = -ENOMEM; goto fail_malloc; } globalmem_setup_cdev(globalmem_devp,0); return 0; fail_malloc: unregister_chrdev_region(devno,1); return ret; } module_init(globalmem_init); static void __exit globalmem_exit(void) { cdev_del(&globalmem_devp->cdev); kfree(globalmem_devp); unregister_chrdev_region(MKDEV(globalmem_major,0),1); } module_exit(globalmem_exit); MODULE_AUTHOR("ztt"); MODULE_LICENSE("GPL v2");
新建Makefile文件,清单如下:
CONFIG_MODULE_SIG=n KVERS = $(shell uname -r) # Kernel modules obj-m += globalmem.o build: kernel_modules kernel_modules: make -C /lib/modules/$(KVERS)/build M=$(CURDIR) modules clean: make -C /lib/modules/$(KVERS)/build M=$(CURDIR) clean
然后在创建的目录下执行命令 make
编译驱动,会在该目录下生成globalmem.ko文件
加载该模块 insmod globalmem.ko
执行 cat /proc/devices
可以看到新定义的字符设备驱动,主设备号为230
执行命令:mknod /dev/globalmem c 230 0
创建“/dev/globalmem”设备节点
通过执行:
echo "hello world" > /dev/globalmem 验证设备的写
cat /dev/globalmem 验证设备的读#输出hello world
进入/sys/module/可以找到globalmem目录 使用tree命令 可观察其目录结构