字符设备驱动程序（实践篇）

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-2.6.31-14-genericPWD := $(shell pwd)obj-m := scull.o modules:$(MAKE) -C $(KERNELDIR) M=$(PWD) modules

 

4. 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：

  在/proc/devices文件里面可以查看到scull的主设备号，假设为251

  sudo su

  mknod /dev/scull0 c 251 0

  mknod /dev/scull1 c 251 1

  mknod /dev/scull2 c 251 2

  mknod /dev/scull3 c 251 3

 

  chgrp staff /dev/scull[0-3]

  chmod 664 /dev/scull[0-3]

 

5. 测试程序scull_test.c

 

#include <fcntl.h>#include <stdlib.h>#include <stdio.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 scullscull_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 scullscull_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);}

 

gcc scull_test.c -o scull_test.o

 

sudo ./scull_test.o

 

结果：

Write 8 bytes to scull
Write 8 bytes to scull
Write 8 bytes to scull
Read 8 bytes from scull
Read 8 bytes from scull
Read 8 bytes from scull
Read "Hello, Character driver!" from scull