学步园

#include <linux/module.h><br /> #include <linux/moduleparam.h><br /> #include <linux/init.h><br /> #include <linux/kernel.h> /* printk() */<br /> #include <linux/slab.h> /* kmalloc() */<br /> #include <linux/fs.h> /* everything... */<br /> #include <linux/errno.h> /* error codes */<br /> #include <linux/types.h> /* size_t */<br /> #include <linux/fcntl.h> /* O_ACCMODE */<br /> #include <linux/cdev.h><br /> #include <asm/system.h> /* cli(), *_flags */<br /> #include <asm/uaccess.h> /* copy_*_user */<br /> #include "scull.h" /* local definitions */<br /> /*<br /> * Our parameters which can be set at load time.<br /> */<br /> //主设备号<br /> int scull_major = SCULL_MAJOR;<br /> //次设备号<br /> int scull_minor = 0;<br /> //请求连续设备编号数量<br /> int scull_nr_devs = SCULL_NR_DEVS; /* number of bare scull devices */<br /> //量子大小<br /> int scull_quantum = SCULL_QUANTUM;<br /> //量子集大小<br /> int scull_qset = SCULL_QSET;<br /> module_param(scull_major, int, S_IRUGO);<br /> module_param(scull_minor, int, S_IRUGO);<br /> module_param(scull_nr_devs, int, S_IRUGO);<br /> module_param(scull_quantum, int, S_IRUGO);<br /> module_param(scull_qset, int, S_IRUGO);<br /> struct scull_dev *scull_devices; /* allocated in scull_init_module */<br /> /*<br /> * Empty out the scull device; must be called with the device<br /> * semaphore held.<br /> */<br /> /*<br /> * 释放整个数据区，简单遍历列表并且释放它发现的任何量子和量子集。<br /> * 在scull_open在文件为写而打开时调用。<br /> * 调用这个函数时必须持有信号量。<br /> */<br /> int scull_trim(struct scull_dev *dev)<br /> {<br /> struct scull_qset *next, *dptr;<br /> //量子集大小<br /> int qset = dev->qset; /* "dev" is not-null */<br /> int i;<br /> for (dptr = dev->data; dptr; dptr = next) { /* all the list items */<br /> if (dptr->data) {//量子集中有数据<br /> //遍历释放当前量子集中的每个量子，量子集大小为qset<br /> for (i = 0; i < qset; i++)<br /> kfree(dptr->data[i]);<br /> //释放量子数组指针<br /> kfree(dptr->data);<br /> dptr->data = NULL;<br /> }<br /> //next获取下一个量子集，释放当前量子集<br /> next = dptr->next;<br /> kfree(dptr);<br /> }<br /> //清理struct scull_dev dev中的变量的值<br /> dev->size = 0;<br /> dev->quantum = scull_quantum;<br /> dev->qset = scull_qset;<br /> dev->data = NULL;<br /> return 0;<br /> }<br /> /*<br /> * Open and close<br /> */<br /> int scull_open(struct inode *inode, struct file *filp)<br /> {<br /> struct scull_dev *dev; /* device information */<br /> dev = container_of(inode->i_cdev, struct scull_dev, cdev);<br /> filp->private_data = dev; /* for other methods */<br /> /* now trim to 0 the length of the device if open was write-only */<br /> //文件以只读模式打开时，截断为0<br /> if ( (filp->f_flags & O_ACCMODE) == O_WRONLY) {<br /> if (down_interruptible(&dev->sem))<br /> return -ERESTARTSYS;<br /> scull_trim(dev); /* ignore errors */<br /> up(&dev->sem);<br /> }<br /> return 0; /* success */<br /> }<br /> int scull_release(struct inode *inode, struct file *filp)<br /> {<br /> return 0;<br /> }<br /> /*<br /> * Follow the list<br /> */<br /> //返回设备dev的第n个量子集的指针，量子集不够n个就申请新的<br /> struct scull_qset *scull_follow(struct scull_dev *dev, int n)<br /> {<br /> //第一个量子集指针<br /> struct scull_qset *qs = dev->data;<br /> /* Allocate first qset explicitly if need be */<br /> // 如果当前设备还没有量子集，就显示分配第一个量子集<br /> if (! qs) {<br /> qs = dev->data = kmalloc(sizeof(struct scull_qset), GFP_KERNEL);<br /> if (qs == NULL)<br /> return NULL; /* Never mind */<br /> memset(qs, 0, sizeof(struct scull_qset));<br /> }<br /> /* Then follow the list */<br /> // 遍历当前设备的量子集链表n步，量子集不够就申请新的<br /> while (n--) {<br /> if (!qs->next) {<br /> qs->next = kmalloc(sizeof(struct scull_qset), GFP_KERNEL);<br /> if (qs->next == NULL)<br /> return NULL; /* Never mind */<br /> memset(qs->next, 0, sizeof(struct scull_qset));<br /> }<br /> qs = qs->next;<br /> continue;<br /> }<br /> return qs;<br /> }<br /> /*<br /> * Data management: read and write<br /> */<br /> ssize_t scull_read( struct file *filp, //设备对应的文件结构<br /> char __user *buf, //读到用户空间<br /> size_t count, //字节数<br /> loff_t *f_pos) //要读的位置，在filp私有数据中的偏移<br /> {<br /> struct scull_dev *dev = filp->private_data;<br /> struct scull_qset *dptr; /* the first listitem */<br /> //量子、量子集大小<br /> int quantum = dev->quantum, qset = dev->qset;<br /> //一个量子集的字节数<br /> int itemsize = quantum * qset; /* how many bytes in the listitem */<br /> int item, s_pos, q_pos, rest;<br /> ssize_t retval = 0;<br /> if (down_interruptible(&dev->sem))<br /> return -ERESTARTSYS;<br /> //要读的位置超过了数据总量<br /> if (*f_pos >= dev->size)<br /> goto out;<br /> //要读的count超出了size，截断count<br /> if (*f_pos + count > dev->size)<br /> count = dev->size - *f_pos;<br /> /* find listitem, qset index, and offset in the quantum */<br /> //在量子/量子集中定位读写位置：第几个量子集，中的第几个量子，在量子中偏移<br /> //第几个量子集<br /> item = (long)*f_pos / itemsize;<br /> //在量子集中的偏移量<br /> rest = (long)*f_pos % itemsize;<br /> //第几个量子，在量子中的偏移<br /> s_pos = rest / quantum; q_pos = rest % quantum;<br /> /* follow the list up to the right position (defined elsewhere) */<br /> //读取要读的量子集的指针<br /> dptr = scull_follow(dev, item);<br /> //读取出错处理<br /> if (dptr == NULL || !dptr->data || ! dptr->data[s_pos])<br /> goto out; /* don't fill holes */<br /> /* read only up to the end of this quantum */<br /> // 只在一个量子中读：如果count超出当前量子，截断count<br /> if (count > quantum - q_pos)<br /> count = quantum - q_pos;<br /> // 将要读位置的内容复制count字节到用户空间buf中<br /> if (copy_to_user(buf, dptr->data[s_pos] + q_pos, count)) {<br /> retval = -EFAULT;<br /> goto out;<br /> }<br /> *f_pos += count;<br /> retval = count;<br /> out:<br /> up(&dev->sem);<br /> return retval;<br /> }<br /> ssize_t scull_write(struct file *filp, const char __user *buf, size_t count,<br /> loff_t *f_pos)<br /> {<br /> struct scull_dev *dev = filp->private_data;<br /> struct scull_qset *dptr;<br /> //量子、量子集大小<br /> int quantum = dev->quantum, qset = dev->qset;<br /> // 一个量子集总字节数<br /> int itemsize = quantum * qset;<br /> int item, s_pos, q_pos, rest;<br /> ssize_t retval = -ENOMEM; /* value used in "goto out" statements */<br /> if (down_interruptible(&dev->sem))<br /> return -ERESTARTSYS;<br /> /* find listitem, qset index and offset in the quantum */<br /> //第几个量子集<br /> item = (long)*f_pos / itemsize;<br /> //在该量子集中的偏移<br /> rest = (long)*f_pos % itemsize;<br /> //在该量子集中的第几个量子，在量子中的偏移<br /> s_pos = rest / quantum; q_pos = rest % quantum;<br /> /* follow the list up to the right position */<br /> //返回该量子集的指针<br /> dptr = scull_follow(dev, item);<br /> if (dptr == NULL)<br /> goto out;<br /> //如果该量子集数据为NULL，就申请一块新内存<br /> if (!dptr->data) {<br /> dptr->data = kmalloc(qset * sizeof(char *), GFP_KERNEL);<br /> if (!dptr->data)<br /> goto out;<br /> memset(dptr->data, 0, qset * sizeof(char *));<br /> }<br /> //如果第s_pos个量子是NULL，就申请一块新内存<br /> if (!dptr->data[s_pos]) {<br /> dptr->data[s_pos] = kmalloc(quantum, GFP_KERNEL);<br /> if (!dptr->data[s_pos])<br /> goto out;<br /> }<br /> /* write only up to the end of this quantum */<br /> // 只在一个量子中写，如果count超出当前量子就截断<br /> if (count > quantum - q_pos)<br /> count = quantum - q_pos;<br /> //从用户空间拷贝数据到内核空间，失败返回没有拷贝的字节数，成功返回0<br /> if (copy_from_user(dptr->data[s_pos]+q_pos, buf, count)) {<br /> retval = -EFAULT;<br /> goto out;<br /> }<br /> *f_pos += count;<br /> retval = count;<br /> /* update the size */<br /> // 更新字节总数大小<br /> if (dev->size < *f_pos)<br /> dev->size = *f_pos;<br /> out:<br /> up(&dev->sem);<br /> return retval;<br /> }</p> <p>struct file_operations scull_fops = {<br /> .owner = THIS_MODULE,<br /> .read = scull_read,<br /> .write = scull_write,<br /> .open = scull_open,<br /> .release = scull_release,<br /> };<br /> /*<br /> * Finally, the module stuff<br /> */<br /> /*<br /> * The cleanup function is used to handle initialization failures as well.<br /> * Thefore, it must be careful to work correctly even if some of the items<br /> * have not been initialized<br /> */<br /> void scull_cleanup_module(void)<br /> {<br /> int i;<br /> //主次设备号合成一个dev_t结构，即设备编号<br /> dev_t devno = MKDEV(scull_major, scull_minor);<br /> /* Get rid of our char dev entries */<br /> if (scull_devices) {<br /> //便利释放每个设备的数据区<br /> for (i = 0; i < scull_nr_devs; i++) {<br /> //释放数据区<br /> scull_trim(scull_devices + i);<br /> //移除cdev<br /> cdev_del(&scull_devices[i].cdev);<br /> }<br /> //释放scull_devices本身<br /> kfree(scull_devices);<br /> }<br /> /* cleanup_module is never called if registering failed */<br /> unregister_chrdev_region(devno, scull_nr_devs);<br /> }</p> <p>/*<br /> * Set up the char_dev structure for this device.<br /> */<br /> // 建立char_dev结构<br /> static void scull_setup_cdev(struct scull_dev *dev, int index)<br /> {<br /> int err, devno = MKDEV(scull_major, scull_minor + index);</p> <p> cdev_init(&dev->cdev, &scull_fops);<br /> dev->cdev.owner = THIS_MODULE;<br /> // dev->cdev.ops = &scull_fops;<br /> //添加字符设备dev->cdev,立即生效<br /> err = cdev_add (&dev->cdev, devno, 1);<br /> /* Fail gracefully if need be */<br /> if (err)<br /> printk(KERN_NOTICE "Error %d adding scull%d", err, index);<br /> }</p> <p>int scull_init_module(void)<br /> {<br /> int result, i;<br /> dev_t dev = 0;<br /> /*<br /> * Get a range of minor numbers to work with, asking for a dynamic<br /> * major unless directed otherwise at load time.<br /> */<br /> //申请设备编号，若在加载时没有指定主设备号就动态分配<br /> if (scull_major) {<br /> dev = MKDEV(scull_major, scull_minor);<br /> result = register_chrdev_region(dev, scull_nr_devs, "scull");<br /> } else {<br /> result = alloc_chrdev_region(&dev, scull_minor, scull_nr_devs,<br /> "scull");<br /> scull_major = MAJOR(dev);<br /> }<br /> if (result < 0) {<br /> printk(KERN_WARNING "scull: can't get major %d/n", scull_major);<br /> return result;<br /> }<br /> /*<br /> * allocate the devices -- we can't have them static, as the number<br /> * can be specified at load time<br /> */<br /> //给scull_dev对象申请内存<br /> scull_devices = kmalloc(scull_nr_devs * sizeof(struct scull_dev), GFP_KERNEL);<br /> if (!scull_devices) {<br /> result = -ENOMEM;<br /> goto fail; /* Make this more graceful */<br /> }<br /> memset(scull_devices, 0, scull_nr_devs * sizeof(struct scull_dev));<br /> /* Initialize each device. */<br /> for (i = 0; i < scull_nr_devs; i++) {<br /> scull_devices[i].quantum = scull_quantum;<br /> scull_devices[i].qset = scull_qset;<br /> //初始化互斥锁，把信号量sem置为1<br /> sema_init(&scull_devices[i].sem, 1);<br /> //init_MUTEX(&scull_devices[i].sem);<br /> //建立char_dev结构<br /> scull_setup_cdev(&scull_devices[i], i);<br /> }<br /> return 0; /* succeed */<br /> fail:<br /> scull_cleanup_module();<br /> return result;<br /> }<br /> module_init(scull_init_module);<br /> module_exit(scull_cleanup_module);<br /> MODULE_AUTHOR("Tekkamanninja");<br /> MODULE_LICENSE("Dual BSD/GPL");