Linux驱动开发之LDD3中第三章scull注释详解
#linux#struct#module#rest#null#semaphore
#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/fcntl.h> /* O_ACCMODE */ #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. */ //主设备号 int scull_major = SCULL_MAJOR; //次设备号 int scull_minor = 0; //请求连续设备编号数量 int scull_nr_devs = SCULL_NR_DEVS; /* number of bare scull devices */ //量子大小 int scull_quantum = SCULL_QUANTUM; //量子集大小 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); struct scull_dev *scull_devices; /* allocated in scull_init_module */ /* * Empty out the scull device; must be called with the device * semaphore held. */ /* * 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。 * 在scull_open在文件为写而打开时调用。 * 调用这个函数时必须持有信号量。 */ int scull_trim(struct scull_dev *dev) { struct scull_qset *next, *dptr; //量子集大小 int qset = dev->qset; /* "dev" is not-null */ int i; for (dptr = dev->data; dptr; dptr = next) { /* all the list items */ if (dptr->data) {//量子集中有数据 //遍历释放当前量子集中的每个量子，量子集大小为qset for (i = 0; i < qset; i++) kfree(dptr->data[i]); //释放量子数组指针 kfree(dptr->data); dptr->data = NULL; } //next获取下一个量子集，释放当前量子集 next = dptr->next; kfree(dptr); } //清理struct scull_dev dev中的变量的值 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 */ //文件以只读模式打开时，截断为0 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 */ //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 struct scull_qset *scull_follow(struct scull_dev *dev, int n) { //第一个量子集指针 struct scull_qset *qs = dev->data; /* Allocate first qset explicitly if need be */ // 如果当前设备还没有量子集，就显示分配第一个量子集 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 */ // 遍历当前设备的量子集链表n步，量子集不够就申请新的 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, //设备对应的文件结构 char __user *buf, //读到用户空间 size_t count, //字节数 loff_t *f_pos) //要读的位置，在filp私有数据中的偏移 { struct scull_dev *dev = filp->private_data; struct scull_qset *dptr; /* the first listitem */ //量子、量子集大小 int quantum = dev->quantum, qset = dev->qset; //一个量子集的字节数 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; //要读的位置超过了数据总量 if (*f_pos >= dev->size) goto out; //要读的count超出了size，截断count if (*f_pos + count > dev->size) count = dev->size - *f_pos; /* find listitem, qset index, and offset in the quantum */ //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 //第几个量子集 item = (long)*f_pos / itemsize; //在量子集中的偏移量 rest = (long)*f_pos % itemsize; //第几个量子，在量子中的偏移 s_pos = rest / quantum; q_pos = rest % quantum; /* follow the list up to the right position (defined elsewhere) */ //读取要读的量子集的指针 dptr = scull_follow(dev, item); //读取出错处理 if (dptr == NULL || !dptr->data || ! dptr->data[s_pos]) goto out; /* don't fill holes */ /* read only up to the end of this quantum */ // 只在一个量子中读：如果count超出当前量子，截断count if (count > quantum - q_pos) count = quantum - q_pos; // 将要读位置的内容复制count字节到用户空间buf中 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; //量子、量子集大小 int quantum = dev->quantum, qset = dev->qset; // 一个量子集总字节数 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 */ //第几个量子集 item = (long)*f_pos / itemsize; //在该量子集中的偏移 rest = (long)*f_pos % itemsize; //在该量子集中的第几个量子，在量子中的偏移 s_pos = rest / quantum; q_pos = rest % quantum; /* follow the list up to the right position */ //返回该量子集的指针 dptr = scull_follow(dev, item); if (dptr == NULL) goto out; //如果该量子集数据为NULL，就申请一块新内存 if (!dptr->data) { dptr->data = kmalloc(qset * sizeof(char *), GFP_KERNEL); if (!dptr->data) goto out; memset(dptr->data, 0, qset * sizeof(char *)); } //如果第s_pos个量子是NULL，就申请一块新内存 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 */ // 只在一个量子中写，如果count超出当前量子就截断 if (count > quantum - q_pos) count = quantum - q_pos; //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 if (copy_from_user(dptr->data[s_pos]+q_pos, buf, count)) { retval = -EFAULT; goto out; } *f_pos += count; retval = count; /* update the size */ // 更新字节总数大小 if (dev->size < *f_pos) dev->size = *f_pos; out: up(&dev->sem); return retval; } struct file_operations scull_fops = { .owner = THIS_MODULE, .read = scull_read, .write = scull_write, .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; //主次设备号合成一个dev_t结构，即设备编号 dev_t devno = MKDEV(scull_major, scull_minor); /* Get rid of our char dev entries */ if (scull_devices) { //便利释放每个设备的数据区 for (i = 0; i < scull_nr_devs; i++) { //释放数据区 scull_trim(scull_devices + i); //移除cdev cdev_del(&scull_devices[i].cdev); } //释放scull_devices本身 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. */ // 建立char_dev结构 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; //添加字符设备dev->cdev,立即生效 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. */ //申请设备编号，若在加载时没有指定主设备号就动态分配 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 */ //给scull_dev对象申请内存 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; //初始化互斥锁，把信号量sem置为1 sema_init(&scull_devices[i].sem, 1); //init_MUTEX(&scull_devices[i].sem); //建立char_dev结构 scull_setup_cdev(&scull_devices[i], i); } return 0; /* succeed */ fail: scull_cleanup_module(); return result; } module_init(scull_init_module); module_exit(scull_cleanup_module); MODULE_AUTHOR("Tekkamanninja"); MODULE_LICENSE("Dual BSD/GPL"); 本篇文章来源于 Linux公社网站(www.linuxidc.com) 原文链接：http://www.linuxidc.com/Linux/2011-06/37819.htm