linux字符設備註冊

頭文件：

#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 <linux/slab.h>
#include <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>

相關內容

2.6內核中使用cdev結構描述一個字符設備。

struct cdev {
	struct kobject kobj;
	struct module *owner;
	const struct file_operations *ops;
	struct list_head list;
	dev_t dev;
	unsigned int count;
};

從dev_t獲取主次設備號

MAJOR(dev_t dev)
MINOR(dev_t dev)

#define MINORBITS 20
#define MINORMASK ((1U << MINORBITS) - 1)

#define MAJOR(dev) ((unsigned int) ((dev) >> MINORBITS))
#define MINOR(dev) ((unsigned int) ((dev) & MINORMASK))
由主設備號和此設備號生成設備號dev_t

MKDEV（int major,int minor）

#define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi))

申請設備號

int register_chrdev_region(dev_t from,unsigned count,const char *name);
int alloc_chrdev_region(dev_t *dev,unsigned baseminor,unsigned count,const char *name);

2.6內核操作cdev的一組函數

void cdev_init(struct cdev *,struct file_operations *);
struct cdev *cdev_alloc(void);
void cdev_put(struct cdev *p);
int cdev_add(struct cdev *,dev_t,unsigned);
void cdev_del(struct cdev *);

struct file_operations {
	struct module *owner;//擁有該模塊的指針，一般賦值爲THIS_MODULES 
	loff_t (*llseek) (struct file *, loff_t, int);
	ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
	ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);//初始化一個異步的讀操作 
	ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);//初始化一個異步的寫操作
	int (*readdir) (struct file *, void *, filldir_t);//僅用於讀取目錄，對於設備文件，該字段爲NULL 
	unsigned int (*poll) (struct file *, struct poll_table_struct *); //輪訓函數，判斷目前是否可以以非阻塞方式讀/寫 
	int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long); 
	long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
	//不適用BLK，的文件系統，用該函數代替ioctl 
	long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
	//64爲系統的32位ioctl將用此函數指針代替 
	int (*mmap) (struct file *, struct vm_area_struct *);//用於將請求的設備內存映射到進程地址空間 
	int (*open) (struct inode *, struct file *);//驅動可不實現該函數，表示打開永遠成功 
	int (*flush) (struct file *, fl_owner_t id);
	int (*release) (struct inode *, struct file *);
	int (*fsync) (struct file *, struct dentry *, int datasync);//刷新待處理的數據 
	int (*aio_fsync) (struct kiocb *, int datasync);//異步 fsync
	int (*fasync) (int, struct file *, int);//通知FASYNC標誌發生變化 
	int (*lock) (struct file *, int, struct file_lock *);
	ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
	unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
	//通常爲NULL 
	int (*check_flags)(int);
	//允許模塊檢查傳遞給fcntl(F_SETEL...)調用的標誌 
	int (*dir_notify)(struct file *filp, unsigned long arg);
	//對文件系統有效，驅動程序不必實現 
	int (*flock) (struct file *, int, struct file_lock *);
	ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
	//VFS調用，將管道數據粘接到文件
	ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
	//VFS調用，將文件數據粘接到管道
	int (*setlease)(struct file *, long, struct file_lock **);
};

void cdev_init(struct cdev *cdev, const struct file_operations *fops)
{
	memset(cdev, 0, sizeof *cdev);
	INIT_LIST_HEAD(&cdev->list);
	kobject_init(&cdev->kobj, &ktype_cdev_default);
	cdev->ops = fops;
}

struct cdev *cdev_alloc(void)
{
	struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
	if (p) {
		INIT_LIST_HEAD(&p->list);
		kobject_init(&p->kobj, &ktype_cdev_dynamic);
	}
	return p;
}

int cdev_add(struct cdev *p, dev_t dev, unsigned count)
{
	p->dev = dev;
	p->count = count;
	return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
}

void cdev_del(struct cdev *p)//調用該函數後需調用unregister_chrdev_region() 釋放申請到的設備號 
{
	cdev_unmap(p->dev, p->count);
	kobject_put(&p->kobj);
}
void unregister_chrdev_region(dev_t from,unsigned count); 

字符驅動模塊加載與卸載函數模板

/*設備結構體*/
struct xxx_dev_t{
	struct cdev cdev;
	...
} xxx_dev;
//驅動模塊加載函數
static int __init xxx_init(void)
{
	...
	cdev_init(&xxx_dev.cdev,&xxx_fops); // 初始化 
	xxx_dev.owmer = THIS_MODULE;
	if(xxx_major){						// 申請設備號 
		register_chdev_region(xxx_dev_no,num,DEV_NAME);
	}else{
		alloc_chrdev_region(&xxx_dev_no,base,num,DEV_NAME);
	}  
	ret = cdev_add(&xxx_dev.cdev,xxx_dev_no,num); // 註冊設備號 
}  
//模塊卸載函數
static void __exit xxx_exit(void)
{
	unregister_chrdev_region(xxx_dev_no,num);
	cdev_del(&xxx_dev.cdev);
	... 
} 

字符設備驅動讀，寫，IO控制模板

ssize_t xxx_read(struct file *filp,char __user *buf,szie_t count,loff_t *f_pos)
{
	...
	copy_to_user(buf,...,...); 
	...
} 
ssize_t xxx_write(struct file *filp,const char __user *buf,szie_t count,loff_t *f_pos)
{
	...
	copy_from_user(...,buf,...); 
	...
} 
/*內核空間與用戶空間不能直接訪問，續借助一下兩個函數，返回值爲不能被賦值的字節數*/ 
unsigned long copy_from_user(void *to, const void __user *from, unsigned long n)
unsigned long copy_to_user( void __user *to, const void *from, unsigned long n)
//複製的是char、int、long可使用put_user()get_user()
int xxx_ioctl(struct inode *inode,struct file *filep,unsigned int cmd,unsigned long arg)
{
	命令有效性檢測
	依據命令類型，檢測參數空間是否可以訪問
	switch(cmd){
	case XXX_CMD1:
		...
		break;
	case XXX_CMD1:
		...
		break; 
	default://不支持的命令 
		return -ENOTTY;	
	} 
	return 0； 
}  
文件操作函數模板
struct file_operations xxx_fops = {
	.owner = THIS_MODULE,
	.read = xxx_read,
	.write = xxx_write,
	.iotcl = xxx_ioctl,
	...
};

驅動中同時包含兩個以上的設備在xxxopen中通過container_of通過結構體成員的指針找到對應結構體的指針

#define container_of(ptr, type, member) ({			\
        const typeof( ((type *)0)->member ) *__mptr = (ptr);	\
        (type *)( (char *)__mptr - offsetof(type,member) );})

當然也可以通過inode結構體中的i_rdev成員獲取其次設備號