字符驱动程序（实践）

1. scull.h

#ifndef _SCULL_H_
#define _SCULL_H_

#ifndef SCULL_MAJOR
#define SCULL_MAJOR 0   /* dynamic major by default */
#endif

#ifndef SCULL_NR_DEVS
#define SCULL_NR_DEVS 4    /* scull0 through scull3 */
#endif

#ifndef SCULL_QUANTUM
#define SCULL_QUANTUM 4000
#endif

#ifndef SCULL_QSET
#define SCULL_QSET    1000
#endif

/*
 * Representation of scull quantum sets.
 */
struct scull_qset {
	void **data;
	struct scull_qset *next;
};

struct scull_dev {
	struct scull_qset *data;  /* Pointer to first quantum set */
	int quantum;              /* the current quantum size */
	int qset;                 /* the current array size */
	unsigned long size;       /* amount of data stored here */
	unsigned int access_key;  /* used by sculluid and scullpriv */
	struct semaphore sem;     /* mutual exclusion semaphore     */
	struct cdev cdev;	  /* Char device structure		*/
};


/*
 * The different configurable parameters
 */
extern int scull_major;     /* main.c */
extern int scull_nr_devs;
extern int scull_quantum;
extern int scull_qset;

#endif /* _SCULL_H_ */

2 scull.c

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>

#include <linux/kernel.h>	/* printk() */
#include <linux/slab.h>		/* kmalloc() */
#include <linux/fs.h>		/* everything... */
#include <linux/errno.h>	/* error codes */
#include <linux/types.h>	/* size_t */
#include <linux/proc_fs.h>
#include <linux/fcntl.h>	/* O_ACCMODE */
#include <linux/seq_file.h>
#include <linux/cdev.h>

#include <asm/system.h>		/* cli(), *_flags */
#include <asm/uaccess.h>	/* copy_*_user */

#include "scull.h"		/* local definitions */

/*
 * Our parameters which can be set at load time.
 */

int scull_major =   SCULL_MAJOR;
int scull_minor =   0;
int scull_nr_devs = SCULL_NR_DEVS;	/* number of bare scull devices */
int scull_quantum = SCULL_QUANTUM;
int scull_qset =    SCULL_QSET;

module_param(scull_major, int, S_IRUGO);
module_param(scull_minor, int, S_IRUGO);
module_param(scull_nr_devs, int, S_IRUGO);
module_param(scull_quantum, int, S_IRUGO);
module_param(scull_qset, int, S_IRUGO);

MODULE_AUTHOR("victorsummer");
MODULE_LICENSE("Dual BSD/GPL");

struct scull_dev *scull_devices;	/* allocated in scull_init_module */


/*
 * Empty out the scull device; must be called with the device
 * semaphore held.
 */
int scull_trim(struct scull_dev *dev)
{
	struct scull_qset *next, *dptr;
	int qset = dev->qset;   /* "dev" is not-null */
	int i;

	for (dptr = dev->data; dptr; dptr = next) { /* all the list items */
		if (dptr->data) {
			for (i = 0; i < qset; i++)
				kfree(dptr->data[i]);
			kfree(dptr->data);
			dptr->data = NULL;
		}
		next = dptr->next;
		kfree(dptr);
	}
	dev->size = 0;
	dev->quantum = scull_quantum;
	dev->qset = scull_qset;
	dev->data = NULL;
	return 0;
}

/*
 * Open and close
 */

int scull_open(struct inode *inode, struct file *filp)
{
	struct scull_dev *dev; /* device information */

	dev = container_of(inode->i_cdev, struct scull_dev, cdev);
	filp->private_data = dev; /* for other methods */

	/* now trim to 0 the length of the device if open was write-only */
	if ( (filp->f_flags & O_ACCMODE) == O_WRONLY) {
		if (down_interruptible(&dev->sem))
			return -ERESTARTSYS;
		scull_trim(dev); /* ignore errors */
		up(&dev->sem);
	}
	return 0;          /* success */
}

int scull_release(struct inode *inode, struct file *filp)
{
	return 0;
}
/*
 * Follow the list
 */
struct scull_qset *scull_follow(struct scull_dev *dev, int n)
{
	struct scull_qset *qs = dev->data;

        /* Allocate first qset explicitly if need be */
	if (! qs) {
		qs = dev->data = kmalloc(sizeof(struct scull_qset), GFP_KERNEL);
		if (qs == NULL)
			return NULL;  /* Never mind */
		memset(qs, 0, sizeof(struct scull_qset));
	}

	/* Then follow the list */
	while (n--) {
		if (!qs->next) {
			qs->next = kmalloc(sizeof(struct scull_qset), GFP_KERNEL);
			if (qs->next == NULL)
				return NULL;  /* Never mind */
			memset(qs->next, 0, sizeof(struct scull_qset));
		}
		qs = qs->next;
		continue;
	}
	return qs;
}

/*
 * Data management: read and write
 */
ssize_t scull_read(struct file *filp, char __user *buf, size_t count,
                loff_t *f_pos)
{
	struct scull_dev *dev = filp->private_data; 
	struct scull_qset *dptr;	/* the first listitem */
	int quantum = dev->quantum, qset = dev->qset;
	int itemsize = quantum * qset; /* how many bytes in the listitem */
	int item, s_pos, q_pos, rest;
	ssize_t retval = 0;

	if (down_interruptible(&dev->sem))
		return -ERESTARTSYS;
	if (*f_pos >= dev->size)
		goto out;
	if (*f_pos + count > dev->size)
		count = dev->size - *f_pos;

	/* find listitem, qset index, and offset in the quantum */
	item = (long)*f_pos / itemsize;
	rest = (long)*f_pos % itemsize;
	s_pos = rest / quantum; q_pos = rest % quantum;

	/* follow the list up to the right position (defined elsewhere) */
	dptr = scull_follow(dev, item);

	if (dptr == NULL || !dptr->data || ! dptr->data[s_pos])
		goto out; /* don't fill holes */

	/* read only up to the end of this quantum */
	if (count > quantum - q_pos)
		count = quantum - q_pos;

	if (copy_to_user(buf, dptr->data[s_pos] + q_pos, count)) {
		retval = -EFAULT;
		goto out;
	}
	*f_pos += count;
	retval = count;

  out:
	up(&dev->sem);
	return retval;
}

ssize_t scull_write(struct file *filp, const char __user *buf, size_t count,
                loff_t *f_pos)
{
	struct scull_dev *dev = filp->private_data;
	struct scull_qset *dptr;
	int quantum = dev->quantum, qset = dev->qset;
	int itemsize = quantum * qset;
	int item, s_pos, q_pos, rest;
	ssize_t retval = -ENOMEM; /* value used in "goto out" statements */

	if (down_interruptible(&dev->sem))
		return -ERESTARTSYS;

	/* find listitem, qset index and offset in the quantum */
	item = (long)*f_pos / itemsize;
	rest = (long)*f_pos % itemsize;
	s_pos = rest / quantum; q_pos = rest % quantum;

	/* follow the list up to the right position */
	dptr = scull_follow(dev, item);
	if (dptr == NULL)
		goto out;
	if (!dptr->data) {
		dptr->data = kmalloc(qset * sizeof(char *), GFP_KERNEL);
		if (!dptr->data)
			goto out;
		memset(dptr->data, 0, qset * sizeof(char *));
	}
	if (!dptr->data[s_pos]) {
		dptr->data[s_pos] = kmalloc(quantum, GFP_KERNEL);
		if (!dptr->data[s_pos])
			goto out;
	}
	/* write only up to the end of this quantum */
	if (count > quantum - q_pos)
		count = quantum - q_pos;

	if (copy_from_user(dptr->data[s_pos]+q_pos, buf, count)) {
		retval = -EFAULT;
		goto out;
	}
	*f_pos += count;
	retval = count;

        /* update the size */
	if (dev->size < *f_pos)
		dev->size = *f_pos;

  out:
	up(&dev->sem);
	return retval;
}

struct file_operations scull_fops = {
	.owner =    THIS_MODULE,
	.llseek =   NULL,
	.read =     scull_read,
	.write =    scull_write,
	.ioctl =    NULL,
	.open =     scull_open,
	.release =  scull_release,
};

/*
 * Finally, the module stuff
 */

/*
 * The cleanup function is used to handle initialization failures as well.
 * Thefore, it must be careful to work correctly even if some of the items
 * have not been initialized
 */
void scull_cleanup_module(void)
{
	int i;
	dev_t devno = MKDEV(scull_major, scull_minor);

	/* Get rid of our char dev entries */
	if (scull_devices) {
		for (i = 0; i < scull_nr_devs; i++) {
			scull_trim(scull_devices + i);
			cdev_del(&scull_devices[i].cdev);
		}
		kfree(scull_devices);
	}

	/* cleanup_module is never called if registering failed */
	unregister_chrdev_region(devno, scull_nr_devs);
}


/*
 * Set up the char_dev structure for this device.
 */
static void scull_setup_cdev(struct scull_dev *dev, int index)
{
	int err, devno = MKDEV(scull_major, scull_minor + index);
    
	cdev_init(&dev->cdev, &scull_fops);
	dev->cdev.owner = THIS_MODULE;
	dev->cdev.ops = &scull_fops;
	err = cdev_add (&dev->cdev, devno, 1);
	/* Fail gracefully if need be */
	if (err)
		printk(KERN_NOTICE "Error %d adding scull%d", err, index);
}


int scull_init_module(void)
{
	int result, i;
	dev_t dev = 0;

/*
 * Get a range of minor numbers to work with, asking for a dynamic
 * major unless directed otherwise at load time.
 */
	if (scull_major) {
		dev = MKDEV(scull_major, scull_minor);
		result = register_chrdev_region(dev, scull_nr_devs, "scull");
	} else {
		result = alloc_chrdev_region(&dev, scull_minor, scull_nr_devs,
				"scull");
		scull_major = MAJOR(dev);
	}
	if (result < 0) {
		printk(KERN_WARNING "scull: can't get major %d/n", scull_major);
		return result;
	}

        /* 
	 * allocate the devices -- we can't have them static, as the number
	 * can be specified at load time
	 */
	scull_devices = kmalloc(scull_nr_devs * sizeof(struct scull_dev), GFP_KERNEL);
	if (!scull_devices) {
		result = -ENOMEM;
		goto fail;  /* Make this more graceful */
	}
	memset(scull_devices, 0, scull_nr_devs * sizeof(struct scull_dev));

        /* Initialize each device. */
	for (i = 0; i < scull_nr_devs; i++) {
		scull_devices[i].quantum = scull_quantum;
		scull_devices[i].qset = scull_qset;
		init_MUTEX(&scull_devices[i].sem);
		scull_setup_cdev(&scull_devices[i], i);
	}

        /* At this point call the init function for any friend device */
	dev = MKDEV(scull_major, scull_minor + scull_nr_devs);

	return 0; /* succeed */

  fail:
	scull_cleanup_module();
	return result;
}

module_init(scull_init_module);
module_exit(scull_cleanup_module);

3 Makefile

KERNELDIR = /usr/src/linux-headers-2.6.35-30-generic  /*改成你内核头文件所在的目录和名称 */
PWD := $(shell pwd)  
 
obj-m := scull.o   

modules:  
	$(MAKE) -C $(KERNELDIR) M=$(PWD) modules  //这行前面要用Tab键空格

4 编译

Lenovo:~/LDD$ make  //在文件所在的目录下

Lenovo:~/LDD$ insmod ./scull.ko  //make之后生成ko文件，insmod之后要建立节点才能被应用程序读写访问：

cat /proc/devices                    //在文件里面可以查看到scull的主设备号

root@caoyin-Lenovo:/home/caoyin/LDD# sudo su
root@caoyin-Lenovo:/home/caoyin/LDD# mknod /dev/scull0 c 250 0
root@caoyin-Lenovo:/home/caoyin/LDD# mknod /dev/scull1 c 250 1
root@caoyin-Lenovo:/home/caoyin/LDD# mknod /dev/scull2 c 250 2
root@caoyin-Lenovo:/home/caoyin/LDD# mknod /dev/scull3 c 250 3
root@caoyin-Lenovo:/home/caoyin/LDD# chgrp staff /dev/scull[0-3]
root@caoyin-Lenovo:/home/caoyin/LDD# chmod 664 /dev/scull[0-3]

在 /dev下面会发先产生了scull0-scull3终端

5 测试程序scull_test.c

#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main()
{
	char *write_buffer = "Hello, Character driver!";
	char *read_buffer = malloc(sizeof(char*)*30);
	int scull_fd = 0;
	int code, back = 0;
	
	// write data to scull
	scull_fd = open("/dev/scull1", O_WRONLY);

	while(*write_buffer != '\0')
	{  
		code = write(scull_fd , write_buffer , 8);
		printf("Write %d bytes to scull/n", code);
		write_buffer += code;
	}

	close(scull_fd);

	// read data from scull
	scull_fd = open("/dev/scull1", O_RDONLY);

	while((code = read(scull_fd , read_buffer , 8)) != 0)
	{
		printf("Read %d bytes from scull/n", code);
		read_buffer += code;
		back += code;
	}
	read_buffer -= back;
	
	printf("Read %s from scull /n", read_buffer); 

	close(scull_fd);

  	exit(0);
  return 0;
}

运行：

root@caoyin-Lenovo:/home/caoyin/LDD# gcc scull_test.c -o scull_test.o
root@caoyin-Lenovo:/home/caoyin/LDD# sudo ./scull_test.o

结果：

Write 8 bytes to scull/nWrite 8 bytes to scull/nWrite 8 bytes to scull/nRead 8 bytes from scull/nRead 8 bytes from scull/nRead 8 bytes from scull/nRead Hello, C