linux特殊设备驱动 .

一. 内存设备结构体

static const struct memdev {const char *name;mode_t mode;const struct file_operations *fops;struct backing_dev_info *dev_info;} devlist[] = { [1] = { "mem", 0, &mem_fops, &directly_mappable_cdev_bdi },#ifdef CONFIG_DEVKMEM [2] = { "kmem", 0, &kmem_fops, &directly_mappable_cdev_bdi },#endif [3] = { "null", 0666, &null_fops, NULL },#ifdef CONFIG_DEVPORT [4] = { "port", 0, &port_fops, NULL },#endif [5] = { "zero", 0666, &zero_fops, &zero_bdi }, [7] = { "full", 0666, &full_fops, NULL }, [8] = { "random", 0666, &random_fops, NULL }, [9] = { "urandom", 0666, &urandom_fops, NULL },[11] = { "kmsg", 0, &kmsg_fops, NULL },#ifdef CONFIG_CRASH_DUMP[12] = { "oldmem", 0, &oldmem_fops, NULL },#endif};

 

二.初始化

     1.内存设备初始化

static int __init chr_dev_init(void){int minor;int err;err = bdi_init(&zero_bdi);if (err)return err;if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))//注册基于内存的设备,捆绑memory_fopsprintk("unable to get major %d for memory devs\n", MEM_MAJOR);mem_class = class_create(THIS_MODULE, "mem");//创建"/sys/class/mem"if (IS_ERR(mem_class))return PTR_ERR(mem_class);mem_class->devnode = mem_devnode;for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {if (!devlist[minor].name)continue;device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),NULL, devlist[minor].name);}//创建devlist数组中的设备"/sys/class/mem/xxx"return tty_init();}

     2.memory_fops

static const struct file_operations memory_fops = {.open = memory_open,.llseek = noop_llseek,};

      3.memory_open

static int memory_open(struct inode *inode, struct file *filp){int minor;const struct memdev *dev;minor = iminor(inode);//根据节点算出次设备号if (minor >= ARRAY_SIZE(devlist))return -ENXIO;dev = &devlist[minor];//根据次设备号获取内存设备if (!dev->fops)return -ENXIO;filp->f_op = dev->fops;//替换操作函数集if (dev->dev_info)filp->f_mapping->backing_dev_info = dev->dev_info;//替换memdev->dev_info/* Is /dev/mem or /dev/kmem ? */if (dev->dev_info == &directly_mappable_cdev_bdi)filp->f_mode |= FMODE_UNSIGNED_OFFSET;if (dev->fops->open)//若存在open方法return dev->fops->open(inode, filp);//则调用其open方法return 0;}

三.null

static const struct file_operations null_fops = {.llseek= null_lseek,.read= read_null,.write= write_null,.splice_write= splice_write_null,};

read_null

static ssize_t read_null(struct file *file, char __user *buf,size_t count, loff_t *ppos){return 0;}

 

write_null

static ssize_t write_null(struct file *file, const char __user *buf,size_t count, loff_t *ppos){return count;}

所以往/dev/null读写数据都是一去不回的,黑洞一般

其他的特殊设备差不多