12.3.6 misc设备驱动
Linux驱动倾向于分层设计，各个具体的设备都可以找到它归属的类型，从而套到它相应的架构里面去，并且只需要实现最底层的那一部分。但是，也有部分类似globalmem、globalfifo的字符设备，确实不知道它属于什么类型，一般推荐大家采用miscdevice框架结构。miscdevice本质上也是字符设备，在miscdevice核心层（drivers/char/misc.c）的misc_init（）函数中，通过register_chrdev(MISC_MAJOR,"misc",&misc_fops)注册字符设备，具体miscdevice实例调用（drivers/char/misc.c）misc_register（）函数又自动完成device_create（）、获取动态次设备号的动作。
miscdevice的主设备号是固定的，MISC_MAJOR定义为10，Linux内核中，大概找到200多处使用miscdevice框架结构的驱动。
miscdevice结构体的定义如代码清单12.21所示。
linux/miscdevice.h
struct miscdevice {
/*minor为MISC_DYNAMIC_MINOR，miscdevice核心层会自动找一个空闲的次设
备号，否则用minor指定的次设备号。*/
const char *name;/*设备的名称*/
const struct file_operations *fops;
struct list_head list;
struct device *parent;
struct device *this_device;
const char *nodename;
umode_t mode;
};
备注：miscdevice结构体内file_operations中的成员函数，实际上是由drivers/char/misc.c中misc驱动核心层的misc_fops成员函数间接调用的，比如misc_open（）就会间接调用底层注册的miscdevice的fops->open。
static int misc_open(struct inode * inode, struct file * file)
{
int minor = iminor(inode);
struct miscdevice *c;
int err = -ENODEV;
const struct file_operations *new_fops = NULL;
mutex_lock(&misc_mtx);
list_for_each_entry(c, &misc_list, list) {
if (c->minor == minor) {
new_fops = fops_get(c->fops);
break;
}
}
if (!new_fops) {
mutex_unlock(&misc_mtx);
request_module("char-major-%d-%d", MISC_MAJOR, minor);
mutex_lock(&misc_mtx);
list_for_each_entry(c, &misc_list, list) {
if (c->minor == minor) {
new_fops = fops_get(c->fops);
break;
}
}
if (!new_fops)
goto fail;
}
err = 0;
replace_fops(file, new_fops);
if (file->f_op->open) {
file->private_data = c;
err = file->f_op->open(inode,file);
}
fail:
mutex_unlock(&misc_mtx);
return err;
}
miscdevice驱动的注册和注销分别用下面两个API：
linux/miscdevice.h
extern int misc_register(struct miscdevice * misc);
extern int misc_deregister(struct miscdevice *misc);
drivers/char/misc.c
/**
* misc_register - register a miscellaneous device
* @misc: device structure
*
* Register a miscellaneous device with the kernel. If the minor
* number is set to %MISC_DYNAMIC_MINOR a minor number is assigned
* and placed in the minor field of the structure. For other cases
* the minor number requested is used.
*
* The structure passed is linked into the kernel and may not be
* destroyed until it has been unregistered.
*
* A zero is returned on success and a negative errno code for
* failure.
*/
int misc_register(struct miscdevice * misc)
{
dev_t dev;
int err = 0;
INIT_LIST_HEAD(&misc->list);
mutex_lock(&misc_mtx);
if (misc->minor == MISC_DYNAMIC_MINOR) {
int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
if (i >= DYNAMIC_MINORS) {
err = -EBUSY;
goto out;
}
misc->minor = DYNAMIC_MINORS - i - 1;
set_bit(i, misc_minors);
} else {
struct miscdevice *c;
list_for_each_entry(c, &misc_list, list) {
if (c->minor == misc->minor) {
err = -EBUSY;
goto out;
}
}
}
dev = MKDEV(MISC_MAJOR, misc->minor);
misc->this_device = device_create(misc_class, misc->parent, dev,
misc, "%s", misc->name); /* 创建设备 */
if (IS_ERR(misc->this_device)) {
int i = DYNAMIC_MINORS - misc->minor - 1;
if (i < DYNAMIC_MINORS && i >= 0)
clear_bit(i, misc_minors);
err = PTR_ERR(misc->this_device);
goto out;
}
/*
* Add it to the front, so that later devices can "override"
* earlier defaults
*/
list_add(&misc->list, &misc_list);
out:
mutex_unlock(&misc_mtx);
return err;
}
EXPORT_SYMBOL(misc_register);
/**
* misc_deregister - unregister a miscellaneous device
* @misc: device to unregister
*
* Unregister a miscellaneous device that was previously
* successfully registered with misc_register(). Success
* is indicated by a zero return, a negative errno code
* indicates an error.
*/
int misc_deregister(struct miscdevice *misc)
{
int i = DYNAMIC_MINORS - misc->minor - 1;
if (WARN_ON(list_empty(&misc->list)))
return -EINVAL;
mutex_lock(&misc_mtx);
list_del(&misc->list);
device_destroy(misc_class, MKDEV(MISC_MAJOR, misc->minor));
if (i < DYNAMIC_MINORS && i >= 0)
clear_bit(i, misc_minors);
mutex_unlock(&misc_mtx);
return 0;
}
EXPORT_SYMBOL(misc_deregister);
备注：
miscdevice驱动的一般结构形如：
static const struct file_operations xxx_fops = {
.unlocked_ioctl = xxx_ioctl,
.mmap = xxx_mmap,
…
};
static struct miscdevice xxx_dev = {
.minor = MISC_DYNAMIC_MINOR, /* 动态分配此设备号 */
.name = "xxx",
.fops = &xxx_fops
};
static int __init xxx_init(void)
{
pr_info("ARC Hostlink driver mmap at 0x%p\n", __HOSTLINK__);
return misc_register(&xxx_dev);
}
linux/miscdevice.h
#define MISC_DYNAMIC_MINOR 255
结论：在调用misc_register（&xxx_dev）时，该函数内部会自动调用device_create（），而device_create（）会以xxx_dev作为drvdata参数。其次，在miscdevice核心层misc_open（）函数的帮助下，在file_operations的成员函数中，xxx_dev会自动成为file的private_data（misc_open会完成file->private_data的赋值操作）。
如果用面向对象的封装思想把一个设备的属性、自旋锁、互斥锁、等待队列、miscdevice等封装在一个结构体里面：
struct xxx_dev {
unsigned int version;
unsigned int size;
spinlock_t lock;
...
struct miscdevice miscdev;
};
在file_operations的成员函数中，可以通过宏container_of（）和file->private_data反推出xxx_dev的实例。
static long xxx_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct xxx_dev *xxx = container_of(file->private_data, struct xxx_dev, miscdev);
...
}
globalfifo驱动基于platform_driver且采用miscdevice框架的结构体实例如下：
1、驱动头文件
#ifndef __GLOBAL_MEM_H
#define __GLOBAL_MEM_H
#include <linux/miscdevice.h>
#include <linux/mutex.h>
#include <linux/wait.h>
#include <linux/fs.h>
#define DRIVER_AUTHOR "[email protected]"
#define DRIVER_DESC "A sample driver"
#define GLOBALFIFO_SIZE 0x1000
#define MEM_CLEAR 0x1
#define DEV_NAME "global_fifo"
/**
*
* 定义全局内存字符设备的结构体:
* 借用面向对象程序设计中“封装”的思想，体现良好的编程习惯。
*
*/
struct globalfifo_dev {
struct miscdevice miscdev;
unsigned int current_len; // FIFO中有效数据的长度
unsigned char mem[GLOBALFIFO_SIZE];
struct mutex mutex; // 互斥锁
wait_queue_head_t r_wait;// 读等待队列头部
wait_queue_head_t w_wait;// 写等待队列头部
struct fasync_struct *async_queue;// 异步通知
};
#endif /* __GLOBAL_MEM_H */
2、平台设备源代码文件
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/platform_device.h>
#include "vichip.h"
#define PLAT_DEV_NAME "globalfifo"
struct platform_device *plat_dev = NULL;
static int __init vi_platform_dev_init(void)
{
int ret;
plat_dev = platform_device_alloc(PLAT_DEV_NAME, -1);
if (!plat_dev)
return -ENOMEM;
ret = platform_device_add(plat_dev);
if (ret) {
printk(KERN_ERR "add platform device fail, ret = [%d]\n", ret);
platform_device_put(plat_dev);
return ret;
}
printk(KERN_INFO "-----vi platform devcie init ok! ret = [%d]----\n", ret);
return 0;
}
static void __exit vi_platform_dev_exit(void)
{
platform_device_unregister(plat_dev);
printk(KERN_INFO "----vi unregister platform devcie success----\n");
}
module_init(vi_platform_dev_init);
module_exit(vi_platform_dev_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);
3、平台驱动源代码文件
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/platform_device.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/sched.h>
#include <linux/poll.h>
#include "vichip.h"
/**
*
* 读写函数
* 让设备结构体globalfifo_dev的mem[]数组与用户空间交互数据，
* 并随着访问的字节数变更更新文件读写偏移位置。
*/
// globalfifo设备驱动的读函数，从设备中读取数据
static ssize_t globalfifo_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
{
int ret;
struct globalfifo_dev *dev = container_of(filp->private_data,
struct globalfifo_dev, miscdev);
DECLARE_WAITQUEUE(wait, current);// 定义并初始化一个名为wait的等待队列元素
mutex_lock(&dev->mutex); // 获取互斥锁
add_wait_queue(&dev->r_wait, &wait); // 把等待队列元素wait添加到读等待队列头部r_wait指向的双向链表中
while (dev->current_len == 0) { // FIFO为空
if (filp->f_flags & O_NONBLOCK) { // 非阻塞
ret = -EAGAIN;
goto out;
}
__set_current_state(TASK_INTERRUPTIBLE);// 改变进程状态TASK_INTERRUPTIBLE,浅度睡眠标记,并没有真正睡眠.
mutex_unlock(&dev->mutex); // 释放互斥锁
schedule();// 让读进程进入睡眠,调度其他进程执行
if (signal_pending(current)) { // 判断是否被信号唤醒
ret = -ERESTARTSYS;
goto out2;
}
mutex_lock(&dev->mutex);
}
if (count > dev->current_len)
count = dev->current_len;
if (copy_to_user(buf, dev->mem, count)) { // 把内核空间中的数据拷贝到用户空间，该函数可能引起阻塞
ret = -EFAULT;
goto out;
} else {
memcpy(dev->mem, dev->mem + count, dev->current_len - count);
dev->current_len -= count;
printk(KERN_INFO "read %d bytes(s),current_len:%d\n", count, dev->current_len);
wake_up_interruptible(&dev->w_wait);// 唤醒可能阻塞的写进程
ret = count;
}
out:
mutex_unlock(&dev->mutex); // 释放互斥锁
out2:
remove_wait_queue(&dev->w_wait, &wait); // 把等待队列元素wait从读等待队列头部r_wait指向的双向链表中移除
set_current_state(TASK_RUNNING); // 设置进程状态为TASK_RUNNING
return ret;
}
// globalfifo设备驱动的写函数，向设备发送数据
static ssize_t globalfifo_write(struct file *filp, const char __user * buf, size_t count, loff_t * ppos)
{
int ret;
struct globalfifo_dev *dev = container_of(filp->private_data,
struct globalfifo_dev, miscdev);
DECLARE_WAITQUEUE(wait, current);// 定义并初始化一个名为wait的等待队列元素
mutex_lock(&dev->mutex);// 获取互斥锁
add_wait_queue(&dev->w_wait, &wait);// 把等待队列元素wait添加到写等待队列头部w_wait指向的双向链表中
while (dev->current_len == GLOBALFIFO_SIZE) { // FIFO为满
if (filp->f_flags & O_NONBLOCK) {
ret = -EAGAIN;
goto out;
}
__set_current_state(TASK_INTERRUPTIBLE);// 改变进程状态TASK_INTERRUPTIBLE,浅度睡眠标记,并没有真正睡眠.
mutex_unlock(&dev->mutex);
schedule();// 让写进程进入睡眠,调度其他进程执行
if (signal_pending(current)) {// 判断是否被信号唤醒
ret = -ERESTARTSYS;
goto out2;
}
mutex_lock(&dev->mutex);
}
if (count > (GLOBALFIFO_SIZE - dev->current_len))
count = GLOBALFIFO_SIZE - dev->current_len;
if (copy_from_user(dev->mem + dev->current_len, buf, count)) { // 把用户空间中的数据写到内核空间,该函数可能引起阻塞
ret = -EFAULT;
goto out;
} else {
dev->current_len += count;
printk(KERN_INFO "written %d bytes(s),current_len:%d\n", count, dev->current_len);
wake_up_interruptible(&dev->r_wait);// 唤醒可能阻塞的读进程
ret = count;
}
out:
mutex_unlock(&dev->mutex); // 释放互斥锁
out2:
remove_wait_queue(&dev->w_wait, &wait);// 把等待队列元素wait从写等待队列头部w_wait指向的双向链表中移除
set_current_state(TASK_RUNNING);// 设置进程状态为TASK_RUNNING
return ret;
}
// globalfifo设备驱动的seek函数
// seek函数对文件定位的起始地址可以是文件开头（SEEK_SET，0）、当前位置（SEEK_CUR，1）和文件尾（SEEK_END，2），假设globalfifo支持从文件开头和当前位置的相对偏移。
// 在定位的时候，应该检查用户请求的合法性，若不合法，函数返回-EINVAL，合法时更新文件的当前位置并返回该位置。
static loff_t globalfifo_llseek(struct file *filp, loff_t offset, int orig)
{
loff_t ret = 0;
switch (orig) {
case 0: /* 从文件开头位置 seek */
if (offset < 0) {
ret = -EINVAL;
break;
}
if ((unsigned int)offset > GLOBALFIFO_SIZE) {
ret = -EINVAL;
break;
}
filp->f_pos = (unsigned int)offset;
ret = filp->f_pos;
break;
case 1: /* 从文件当前位置开始 seek */
if ((filp->f_pos + offset) > GLOBALFIFO_SIZE) {
ret = -EINVAL;
break;
}
if ((filp->f_pos + offset) < 0) {
ret = -EINVAL;
break;
}
filp->f_pos += offset;
ret = filp->f_pos;
break;
default:
ret = -EINVAL;
break;
}
return ret;
}
// ioctl函数
// globalfifo设备驱动的ioctl函数接受MEM_CLEAR命令，这个命令会将全局内存的有效数据长度清0，对于设备不支持的命令，ioctl函数应该返回-EINVAL。
static long globalfifo_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
struct globalfifo_dev *dev = container_of(filp->private_data,
struct globalfifo_dev, miscdev);
switch (cmd) {
case MEM_CLEAR:
memset(dev->mem, 0, GLOBALFIFO_SIZE); // 清空内存
printk(KERN_INFO "globalfifo is set to zero\n");
break;
default:
return -EINVAL;
}
return 0;
}
static int globalfifo_fasync(int fd, struct file *filp, int mode)
{
struct globalfifo_dev *dev = container_of(filp->private_data,
struct globalfifo_dev, miscdev);
return fasync_helper(fd, filp, mode, &dev->async_queue);
}
static int globalfifo_open(struct inode *inode, struct file *filep)
{
printk(KERN_INFO "globalfifo_open\n");
return 0; /* 成功 */
}
static int globalfifo_release(struct inode *inode, struct file *filep)
{
printk(KERN_INFO "globalfifo_release\n");
globalfifo_fasync(-1, filep, 0);
return 0;
}
static unsigned int globalfifo_poll (struct file *filep, struct poll_table_struct *wait)
{
unsigned int mask = 0;
struct globalfifo_dev *dev = container_of(filep->private_data,
struct globalfifo_dev, miscdev);
mutex_lock(&dev->mutex);
poll_wait(filep, &dev->r_wait, wait); // 加入读等待队列
poll_wait(filep, &dev->w_wait, wait); // 加入写等待队列
if (dev->current_len != 0) { // 可读(FIFO非空)
mask |= POLLIN | POLLRDNORM; // 设置位掩码
}
if (dev->current_len != GLOBALFIFO_SIZE) { // 可写(FIFO非满)
mask |= POLLOUT | POLLWRNORM; // 设置位掩码
}
mutex_unlock(&dev->mutex);
return mask;
}
// globalfifo设备驱动的文件操作结构体
static const struct file_operations globalfifo_fops = {
.owner = THIS_MODULE,
.llseek = globalfifo_llseek,
.read = globalfifo_read,
.write = globalfifo_write,
.unlocked_ioctl = globalfifo_ioctl,
.open = globalfifo_open,
.release = globalfifo_release,
.poll = globalfifo_poll,
.fasync = globalfifo_fasync,
};
static int globalfifo_probe(struct platform_device *pdev)
{
struct globalfifo_dev *globalfifo_devp = NULL;
int ret;
globalfifo_devp = devm_kzalloc(&pdev->dev, sizeof(*globalfifo_devp), GFP_KERNEL);
if (!globalfifo_devp)
return -ENOMEM;
globalfifo_devp->miscdev.minor = MISC_DYNAMIC_MINOR;
globalfifo_devp->miscdev.name = DEV_NAME;
globalfifo_devp->miscdev.fops = &globalfifo_fops;
mutex_init(&globalfifo_devp->mutex); // 初始化互斥锁
init_waitqueue_head(&globalfifo_devp->r_wait);// 初始化读等待队列头部
init_waitqueue_head(&globalfifo_devp->w_wait);// 初始化写等待队列头部
platform_set_drvdata(pdev, globalfifo_devp); // 设置驱动数据
printk(KERN_INFO "%s driver found device!!\n", __func__);
ret = misc_register(&globalfifo_devp->miscdev); // 注册混杂设备
if (ret < 0)
goto err;
return 0;
err:
return ret;
}
static int globalfifo_remove(struct platform_device *pdev)
{
struct globalfifo_dev *gl = platform_get_drvdata(pdev); // 获取驱动数据
misc_deregister(&gl->miscdev); // 注销混杂设备
printk(KERN_INFO "%s driver found device unpluged!!\n", __func__);
return 0;
}
static struct platform_driver globalfifo_driver = {
.driver = {
.name = "globalfifo",
.owner = THIS_MODULE,
},
.probe = globalfifo_probe,
.remove = globalfifo_remove,
};
module_platform_driver(globalfifo_driver);
#if 0
/* module_platform_driver() - Helper macro for drivers that don't do
* anything special in module init/exit. This eliminates a lot of
* boilerplate. Each module may only use this macro once, and
* calling it replaces module_init() and module_exit()
* #include <linux/platform_device.h>
*/
#define module_platform_driver(__platform_driver) \
module_driver(__platform_driver, platform_driver_register, \
platform_driver_unregister)
/*
* module_driver() - Helper macro for drivers that don't do anything
* special in module init/exit. This eliminates a lot of boilerplate.
* Each module may only use this macro once, and calling it replaces
* module_init() and module_exit().
*
* @__driver: driver name
* @__register: register function for this driver type
* @__unregister: unregister function for this driver type
* @...: Additional arguments to be passed to __register and __unregister.
*
* Use this macro to construct bus specific macros for registering
* drivers, and do not use it on its own.
* #include <linux/device.h>
*/
#define module_driver(__driver, __register, __unregister, ...) \
static int __init __driver##_init(void) \
{ \
return __register(&(__driver) , ##__VA_ARGS__); \
} \
module_init(__driver##_init); \
static void __exit __driver##_exit(void) \
{ \
__unregister(&(__driver) , ##__VA_ARGS__); \
} \
module_exit(__driver##_exit);
#endif
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);
4、Makefile
CONFIG_MODULE_SIG=n
ifeq ($(KERNELRELEASE),)
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
all:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
clean:
$(MAKE) -C $(KERNELDIR) M=$(PWD) clean
else
obj-m := vi_plat_dev.o vi_plat_dri.o
endif
5、测试文件
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <stdio.h>
#define DEV_NAME "/dev/global_fifo"
#define FIFO_CLEAR 0x1
#define BUFFER_LEN 20
void main(void)
{
int fd, num;
char rd_ch[BUFFER_LEN];
fd_set rfds, wfds; /* 读/写文件描述符集 */
/* 以非阻塞、只读方式打开设备文件:/dev/globalfifo */
fd = open(DEV_NAME, O_RDONLY | O_NONBLOCK);
if (fd != -1) {
/* FIFO清0 */
if (ioctl(fd, FIFO_CLEAR, 0) < 0)
printf("ioctl command failed\n");
while (1) {
FD_ZERO(&rfds);//清除一个读文件描述符集合
FD_ZERO(&wfds);
FD_SET(fd, &rfds);//将一个文件描述符fd加入读文件描述符集合中
FD_SET(fd, &wfds);
select(fd + 1, &rfds, &wfds, NULL, NULL);// 多路复用IO select(应用程序)->poll(驱动程序)
/* 数据可获得 */
if (FD_ISSET(fd, &rfds))// 判断文件描述符是否被置位:可读
printf("Poll monitor:can be read\n");
/* 数据可写入 */
if (FD_ISSET(fd, &wfds))// 判断文件描述符是否被置位:可写
printf("Poll monitor:can be written\n");
}
} else {
printf("Device open failure\n");
}
close(fd);
}
6、验证结果：
1）sudo insmod vi_plat_dev .ko
2）sudo insmod vi_plat_dri.ko
3）修改设备文件权限 sudo chmod 0777 /dev/global_fifo
4）./test
结论：当没有任何输入，即FIFO为空时，程序不断地输出Poll monitor：can be written，通过echo向/dev/global_fifo写入一些数据后，将输出Poll monitor：can be read和Poll monitor：can be written，如果不断地通过echo向/dev/global_fifo写入数据直至写满FIFO，则发现pollmonitor程序将只输出Poll monitor：can be read。对于globalfifo而言，不会出现既不能读，又不能写的情况。