LinuxDeviceDrivers3(包括源码注解）

/* * main.c -- the bare scull char module * * 此代码为ldd3例子，自己加了些注释;希望可以和更多有着同样兴趣的鸟儿们一块学习讨论。 * 哪有注释的不对的地方请发mail给我，或留言； * * author : liyangth@gmail.com * * date: 2007-2-7 * * Note：注释的每一个关键的段都以[tag00]作了标签，大家可以按照tag的顺序阅读； * e.g: 搜索 "Tag000" */ #include <linux/config.h> #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; /* * 模块参数，可在模块转载时赋值，很灵活方便； * e.g: * insmod scull.ko scull_major=111 scull_nr_devs=3 scull_quantum=1000 * *[形参说明] * 1 -- 变量名； * 2 -- 变量类型； * 3 -- sysfs入口项的访问许可掩码（一般用S_IRUGO就成）； */ module_param(scull_major, 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("Alessandro Rubini, Jonathan Corbet"); MODULE_LICENSE("Dual BSD/GPL"); struct scull_dev *scull_devices; /* allocated in scull_init_module */ /* Note: 不要把它理解成一个指向scull_dev结构的指针, 它其实是一个scull_dev结构数组,等待下面kmalloc分配多个我们scull设备空间 */ /* * Empty out the scull device; 就像销毁链表,和理解如何编写一个字符驱动没有关系,可以不看; * * must be called with the device semaphore held. 要注意一下了,肯定是要同步的; * */ 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; } //Start: [Tag003] proc的实现,可以先不看; #ifdef SCULL_DEBUG /* use proc only if debugging */ //这个是老方法实现的proc /* * The proc filesystem: function to read and entry */ int scull_read_procmem(char *buf, char **start, off_t offset, int count, int *eof, void *data) { int i, j, len = 0; int limit = count - 80; /* Don't print more than this */ for (i = 0; i < scull_nr_devs && len <= limit; i++) { struct scull_dev *d = &scull_devices[i]; struct scull_qset *qs = d->data; if (down_interruptible(&d->sem)) return -ERESTARTSYS; len += sprintf(buf+len,"\nDevice %i: qset %i, q %i, sz %li\n", i, d->qset, d->quantum, d->size); for (; qs && len <= limit; qs = qs->next) { /* scan the list */ len += sprintf(buf + len, " item at %p, qset at %p\n", qs, qs->data); if (qs->data && !qs->next) /* dump only the last item */ for (j = 0; j < d->qset; j++) { if (qs->data[j]) len += sprintf(buf + len, " % 4i: %8p\n", j, qs->data[j]); } } up(&scull_devices[i].sem); } *eof = 1; return len; } //下面的是用新方法实现的 /* * For now, the seq_file implementation will exist in parallel. The * older read_procmem function should maybe go away, though. */ /* * Here are our sequence iteration methods. Our "position" is * simply the device number. */ static void *scull_seq_start(struct seq_file *s, loff_t *pos) { if (*pos >= scull_nr_devs) return NULL; /* No more to read */ return scull_devices + *pos; } static void *scull_seq_next(struct seq_file *s, void *v, loff_t *pos) { (*pos)++; if (*pos >= scull_nr_devs) return NULL; return scull_devices + *pos; } static void scull_seq_stop(struct seq_file *s, void *v) { /* Actually, there's nothing to do here */ } static int scull_seq_show(struct seq_file *s, void *v) { struct scull_dev *dev = (struct scull_dev *) v; struct scull_qset *d; int i; if (down_interruptible(&dev->sem)) return -ERESTARTSYS; seq_printf(s, "\nDevice %i: qset %i, q %i, sz %li\n", (int) (dev - scull_devices), dev->qset, dev->quantum, dev->size); for (d = dev->data; d; d = d->next) { /* scan the list */ seq_printf(s, " item at %p, qset at %p\n", d, d->data); if (d->data && !d->next) /* dump only the last item */ for (i = 0; i < dev->qset; i++) { if (d->data[i]) seq_printf(s, " % 4i: %8p\n", i, d->data[i]); } } up(&dev->sem); return 0; } /* * Tie the sequence operators up. */ static struct seq_operations scull_seq_ops = { .start = scull_seq_start, .next = scull_seq_next, .stop = scull_seq_stop, .show = scull_seq_show }; /* * Now to implement the /proc file we need only make an open * method which sets up the sequence operators. */ static int scull_proc_open(struct inode *inode, struct file *file) { return seq_open(file, &scull_seq_ops); } /* * Create a set of file operations for our proc file. */ static struct file_operations scull_proc_ops = { .owner = THIS_MODULE, .open = scull_proc_open, .read = seq_read, .llseek = seq_lseek, .release = seq_release }; /* * Actually create (and remove) the /proc file(s). */ //分别用新老方法实现了二个proc文件 static void scull_create_proc(void) { struct proc_dir_entry *entry; create_proc_read_entry("scullmem", 0 /* default mode */, NULL /* parent dir */, scull_read_procmem, NULL /* client data */); entry = create_proc_entry("scullseq", 0, NULL); if (entry) entry->proc_fops = &scull_proc_ops; } static void scull_remove_proc(void) { /* no problem if it was not registered */ remove_proc_entry("scullmem", NULL /* parent dir */); remove_proc_entry("scullseq", NULL); } #endif /* SCULL_DEBUG */ //End /* 开始实现对设备操作的方法集了,关键!!! */ /* * Open and close */ //[Tag004] /* open应完成的工作有： 1.检查设备特定的错误（诸如设备未就绪或类似的硬件问题） 2.如果设备是首次打开，则对其进行初始化； 3.如有必要，更新f_op指针； 4.分配并填写filp->private_data；（在这里我们只实现这项即可） */ /* [形参说明] struct inode *inode -- 用它的i_cdev成员得到dev; struct file *filp -- 将得到的dev存放到他的成员private_data中； */ 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); /* [说明] 1.我们要填充的应该是我们自己的特殊设备，而不是钳在他里面的字符设备结构； 2.inode结构的i_cdev成员这能提供基本字符设备结构； 3.这里利用了定义在<linux/kernel.h>中的宏来实现通过cdev得到dev; */ /* 以后read , write ,等操作的实现中就靠他来得到dev了； */ 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 */ } /* close device file, in here we do nothing */ /* * [Tag005] * close应完成的工作有： * 1.释放由open分配的，保存在filp->private_data中的所有内容； * 2.在最后一次关闭操作时关闭设备； * [注意：]并不是每次的close系统调用都会去调用到release. 在open时，也仅在open时才会创建 * 一个新的数据结构；在fork, dup时只是增加了这个结构中维护的一个引用计数； * 所以当这个引用计数为0时，调用的close才意味着要释放设备数据结构，此时release才会被调用； */ int scull_release(struct inode *inode, struct file *filp) { return 0; } /* * Follow the list * * 第一次调用时用于创建链表； * 然后就是找到第n个节点；