Linux设备驱动学习(2) 全局内存“设备” scull
这次分析的是LDD3中的第一个程序scull
scull设备也是一个内存”设备“
结构图如下，来自LDD3
/*
* Representation of scull quantum sets.
*/
struct scull_qset {
void **data;//指针的指针,(*data)是一个指针变量，指示一片内存空间，这片内存中间内存储的也是地址
struct scull_qset *next;
};
struct scull_dev {
struct scull_qset *data; /* Pointer to first quantum set *///第一个scull_qset的地址
int quantum; /* the current quantum size *///每一个数据块的大小
int qset; /* the current array size *///每个scull_qset包含多少个指针
unsigned long size; /* amount of data stored here *///设备中有多少可用的数据内存，也就是Quantum中的内存数据。
unsigned int access_key; /* used by sculluid and scullpriv */
struct semaphore sem; /* mutual exclusion semaphore *///信号量
struct cdev cdev; /* Char device structure *///字符设备结构
};
//主程序
/*
* main.c -- the bare scull char module
*
* Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
* Copyright (C) 2001 O'Reilly & Associates
*
* The source code in this file can be freely used, adapted,
* and redistributed in source or binary form, so long as an
* acknowledgment appears in derived source files. The citation
* should list that the code comes from the book "Linux Device
* Drivers" by Alessandro Rubini and Jonathan Corbet, published
* by O'Reilly & Associates. No warranty is attached;
* we cannot take responsibility for errors or fitness for use.
*
*/
#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; //4000
int scull_qset = SCULL_QSET; //1000
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("Alessandro Rubini, Jonathan Corbet");
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.
*///释放数据结构，最后剩下scull_dev结构
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++)//遍历指针数组中的每个元素，释放其所指的空间
kfree(dptr->data[i]);
kfree(dptr->data); //最后释放这个指针数组。
dptr->data = NULL; //置空
}
next = dptr->next;
kfree(dptr); //释放scull_qset结构
}
dev->size = 0; //表示设备拥有的可读写的数据内存
dev->quantum = scull_quantum; //重置各个参数
dev->qset = scull_qset;
dev->data = NULL;
return 0;
}
#ifdef SCULL_DEBUG /* use proc only if debugging */
/*
* 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;
}
/*
* 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).
*/
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);//create a read-only file in /proc
if (entry)
entry->proc_fops = &scull_proc_ops;//关联文件和对应的文件操作函数集
}
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 */
/*
* 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);//经典的一个宏，cdev是scull_dev中的一个成员，现在有cdev的指针inode->i_cdev得到scull_dev的指针
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)) //清空前先得到信号量
return -ERESTARTSYS;
scull_trim(dev); /* ignore errors */
up(&dev->sem); //清空后释放信号量
}
return 0; /* success */
}
int scull_release(struct inode *inode, struct file *filp)
{
return 0;
}
/*
* Follow the list
*/ //得到第n个scull_qset的结构体指针（从0开始）
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) {//为第一个scull_qset分配空间
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; //先得到设备的指针
struct scull_qset *dptr; /* the first listitem */
int quantum = dev->quantum, qset = dev->qset;
int itemsize = quantum * qset; /* how many bytes in the listitem *///在一个scull_qset中总共有itemsize个字节可使用。
int item, s_pos, q_pos, rest;
ssize_t retval = 0;
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
if (*f_pos >= dev->size) //*f_pos表示已读的字节数
goto out;
if (*f_pos + count > dev->size)
count = dev->size - *f_pos;
/* find listitem, qset index, and offset in the quantum *///这里举个例子比较好，比如*f_pos为4000*1000+4000*500+100
item = (long)*f_pos / itemsize; //找到是第几个scull_qset结构（从第0个开始），例子里就是1了
rest = (long)*f_pos % itemsize; //找到在1000个指针数组中指向的数据块中的偏移（从第0个开始），例子里就是4000*500+100
s_pos = rest / quantum; q_pos = rest % quantum;//q_pos找到在这块4000B的空间里的偏移（0～3999）
//s_pos找到是在第几个指针指向的数据块中，（从0开始）
/* follow the list up to the right position (defined elsewhere) */
dptr = scull_follow(dev, item);//找到第item个scull_qset结构，（从第0个开始）
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) //最多只读完这个数据块4000B
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); //释放信号量
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 *///写和读类似
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)//更新设备拥有的数据内存
dev->size = *f_pos;
out:
up(&dev->sem);
return retval;
}
/*
* The ioctl() implementation
*/
int scull_ioctl(struct inode *inode, struct file *filp,
unsigned int cmd, unsigned long arg)
{
int err = 0, tmp;
int retval = 0;
/*
* extract the type and number bitfields, and don't decode
* wrong cmds: return ENOTTY (inappropriate ioctl) before access_ok()
*/
if (_IOC_TYPE(cmd) != SCULL_IOC_MAGIC) return -ENOTTY;
if (_IOC_NR(cmd) > SCULL_IOC_MAXNR) return -ENOTTY;
/*
* the direction is a bitmask, and VERIFY_WRITE catches R/W
* transfers. `Type' is user-oriented, while
* access_ok is kernel-oriented, so the concept of "read" and
* "write" is reversed
*/
if (_IOC_DIR(cmd) & _IOC_READ)
err = !access_ok(VERIFY_WRITE, (void __user *)arg, _IOC_SIZE(cmd));
else if (_IOC_DIR(cmd) & _IOC_WRITE)
err = !access_ok(VERIFY_READ, (void __user *)arg, _IOC_SIZE(cmd));
if (err) return -EFAULT;
switch(cmd) {
case SCULL_IOCRESET:
scull_quantum = SCULL_QUANTUM;
scull_qset = SCULL_QSET;
break;
case SCULL_IOCSQUANTUM: /* Set: arg points to the value */
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
retval = __get_user(scull_quantum, (int __user *)arg);
break;
case SCULL_IOCTQUANTUM: /* Tell: arg is the value */
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
scull_quantum = arg;
break;
case SCULL_IOCGQUANTUM: /* Get: arg is pointer to result */
retval = __put_user(scull_quantum, (int __user *)arg);
break;
case SCULL_IOCQQUANTUM: /* Query: return it (it's positive) */
return scull_quantum;
case SCULL_IOCXQUANTUM: /* eXchange: use arg as pointer */
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
tmp = scull_quantum;
retval = __get_user(scull_quantum, (int __user *)arg);
if (retval == 0)
retval = __put_user(tmp, (int __user *)arg);
break;
case SCULL_IOCHQUANTUM: /* sHift: like Tell + Query */
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
tmp = scull_quantum;
scull_quantum = arg;
return tmp;
case SCULL_IOCSQSET:
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
retval = __get_user(scull_qset, (int __user *)arg);
break;
case SCULL_IOCTQSET:
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
scull_qset = arg;
break;
case SCULL_IOCGQSET:
retval = __put_user(scull_qset, (int __user *)arg);
break;
case SCULL_IOCQQSET:
return scull_qset;
case SCULL_IOCXQSET:
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
tmp = scull_qset;
retval = __get_user(scull_qset, (int __user *)arg);
if (retval == 0)
retval = put_user(tmp, (int __user *)arg);
break;
case SCULL_IOCHQSET:
if (! capable (CAP_SYS_ADMIN))
return -EPERM;
tmp = scull_qset;
scull_qset = arg;
return tmp;
/*
* The following two change the buffer size for scullpipe.
* The scullpipe device uses this same ioctl method, just to
* write less code. Actually, it's the same driver, isn't it?
*/
case SCULL_P_IOCTSIZE:
scull_p_buffer = arg;
break;
case SCULL_P_IOCQSIZE:
return scull_p_buffer;
default: /* redundant, as cmd was checked against MAXNR */
return -ENOTTY;
}
return retval;
}
/*
* The "extended" operations -- only seek
*/
loff_t scull_llseek(struct file *filp, loff_t off, int whence)
{
struct scull_dev *dev = filp->private_data;
loff_t newpos;
switch(whence) {
case 0: /* SEEK_SET */
newpos = off;
break;
case 1: /* SEEK_CUR */
newpos = filp->f_pos + off;
break;
case 2: /* SEEK_END */
newpos = dev->size + off;
break;
default: /* can't happen */
return -EINVAL;
}
if (newpos < 0) return -EINVAL;
filp->f_pos = newpos;
return newpos;
}
struct file_operations scull_fops = {
.owner = THIS_MODULE,
.llseek = scull_llseek,
.read = scull_read,
.write = scull_write,
.ioctl = scull_ioctl,
.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);
}
#ifdef SCULL_DEBUG /* use proc only if debugging */
scull_remove_proc();
#endif
/* cleanup_module is never called if registering failed */
unregister_chrdev_region(devno, scull_nr_devs);
/* and call the cleanup functions for friend devices */
scull_p_cleanup();
scull_access_cleanup();
}
/*
* 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);//静态分配，分配scull_nr_devs个设备号
result = register_chrdev_region(dev, scull_nr_devs, "scull");
} else { //动态分配
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);//为设备结构体分配空间
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); //信号量在模块初始化时便已设置
scull_setup_cdev(&scull_devices[i], i);//初始化字符设备cdev，次设备号为i
}
/* At this point call the init function for any friend device */
dev = MKDEV(scull_major, scull_minor + scull_nr_devs);//生成后续的总设备号
dev += scull_p_init(dev);//scull_p_init()返回pipe设备数目
dev += scull_access_init(dev);
#ifdef SCULL_DEBUG /* only when debugging */
scull_create_proc();
#endif
return 0; /* succeed */
fail:
scull_cleanup_module();
return result;
}
module_init(scull_init_module);
module_exit(scull_cleanup_module);
关于对proc文件系统的操作没有深入探查，我会在后面的学习中逐步研究的。