Linux驱动开发之LDD3中第三章scull注释详解【转】

#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");