1 五种IO模型------读写外设数据的方式
阻塞: 不能操作就睡觉
非阻塞：不能操作就返回错误(通过轮询即才能实现阻塞的情况 ）
多路复用：委托中介监控
信号驱动：让内核如果能操作时发信号，在信号处理函数中操作
异步IO：向内核注册操作请求，内核完成操作后发通知信号
2 阻塞与非阻塞
应用层：
open时由O_NONBLOCK指示read、write时是否阻塞
open以后可以由fcntl函数来改变是否阻塞：
flags = fcntl(fd,F_GETFL,0); //获取当前设备中标志位
flags |= O_NONBLOCK; //增加不阻塞标志位
fcntl(fd, F_SETFL, flags); //设置当前标志位到设备中驱动层：通过等待队列
wait_queue_head_t //等待队列头数据类型
init_waitqueue_head(wait_queue_head_t *pwq) //初始化等待队列头
wait_event_interruptible(wq,condition)
/*
功能：条件不成立则让任务进入浅度睡眠，直到条件成立醒来
wq:等待队列头
condition：C语言表达式
返回：正常唤醒返回0，信号唤醒返回非0（此时读写操作函数应返回-ERESTARTSYS）
*/
wait_event(wq,condition) //深度睡眠
wake_up_interruptible(wait_queue_head_t *pwq)
wake_up(wait_queue_head_t *pwq)
/*
1. 读、写用不同的等待队列头rq、wq
2. 无数据可读、可写时调用wait_event_interruptible(rq、wq,条件)
3. 写入数据成功时唤醒rq，读出数据成功唤醒wq
*/
2.1 示例
mychar.c
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>
#include <linux/wait.h>
#include <linux/sched.h>
#include "mychar.h"
#define BUF_LEN 100
#define MYCHAR_DEV_CNT 3
int major = 11;
int minor = 0;
int mychar_num = MYCHAR_DEV_CNT;
//新建结构体类型
struct mychar_dev
{
struct cdev mydev;
char mydef_buf[BUF_LEN]; //相当于结构体的私有变量
int curlen; //相当于结构体的私有变量
wait_queue_head_t rq; //等待读队列
wait_queue_head_t wq; //等待写队列
};
struct mychar_dev gmydev;
int mychar_open(struct inode *pnode, struct file *pfile)
{
//利用private_data私有变量来指向全局变量结构体地址
pfile->private_data = (void*)(container_of(pnode->i_cdev,struct mychar_dev,mydev));
printk("mychar_open is called\n");
return 0;
}
int mychar_close(struct inode *pnode, struct file *pfile)
{
printk("mychar_close is called\n");
return 0;
}
ssize_t mychar_read(struct file *filp, char __user *pbuf, size_t count, loff_t *ppos)
{
int ret = 0;
int size = 0;
//获取全家变量结构体地址
struct mychar_dev *pmydev = (struct mychar_dev *)filp->private_data;
if(pmydev->curlen <= 0)
{
if(filp->f_flags & O_NONBLOCK)
{//非阻塞
printk("O_NONBLOCK No Data Read\n");
return -1;
}
else
{//阻塞
ret = wait_event_interruptible(pmydev->rq,pmydev->curlen > 0);
if(ret)
{
printk("Wake up by signal\n");
return -ERESTARTSYS;
}
}
}
if(count > pmydev->curlen)
{
size = pmydev->curlen;
}
else
{
size = count;
}
//将内核空间中的数据复制到用户空间
ret = copy_to_user(pbuf,pmydev->mydef_buf,size);
if(ret)
{
printk("copy_to_user failed\n");
return -1;
}
//读完之后把后面的内容再拷贝过来，同时更新curlen
memcpy(pmydev->mydef_buf,pmydev->mydef_buf+size,pmydev->curlen - size);
pmydev->curlen = pmydev->curlen - size;
wake_up_interruptible(&pmydev->wq);
return size;
}
ssize_t mychar_write (struct file *filp, const char __user *pbuf, size_t count, loff_t *ppos)
{
int size = 0;
int ret = 0;
//获取全家变量结构体地址
struct mychar_dev *pmydev = (struct mychar_dev *)filp->private_data;
if(pmydev->curlen >= BUF_LEN)
{
if(filp->f_flags & O_NONBLOCK)
{
printk("O_NONBLOCK Can not write data\n");
return -1;
}
else
{
ret = wait_event_interruptible(pmydev->wq,pmydev->curlen < BUF_LEN);
if(ret)
{
printk("wake up by signal\n");
return -ERESTARTSYS;
}
}
}
if(count > BUF_LEN - pmydev->curlen)
{
size = BUF_LEN - pmydev->curlen;
}
else
{
size = count;
}
//将用户空间中的数据复制到内核空间中
ret = copy_from_user(pmydev->mydef_buf + pmydev->curlen, pbuf, size);
if(ret)
{
printk("copy_from_user failed\n");
return -1;
}
//更新curlen
pmydev->curlen = pmydev->curlen + size;
wake_up_interruptible(&pmydev->rq);
return size;
}
long mychar_ioctl(struct file *filp, unsigned int cmd,unsigned long arg)
{
int __user *pret = (int *)arg;
int maxlen = BUF_LEN;
int ret = 0;
struct mychar_dev *pmydev = (struct mychar_dev *)filp->private_data;
switch(cmd)
{
case MYCHAR_IOCTL_GET_MAXLEN:
ret = copy_to_user(pret,&maxlen,sizeof(int));
if(ret)
{
printk("copy_to_user MAXLEN failed\n");
return -1;
}
break;
case MYCHAR_IOCTL_GET_CURLEN:
ret = copy_to_user(pret,&pmydev->curlen,sizeof(int));
if(ret)
{
printk("copy_to_user CURLEN failed\n");
return -1;
}
break;
default:
printk("The cmd is unknow\n");
return -1;
}
return 0;
}
//结构体初始化:部分变量赋值初始化
struct file_operations myops = {
.owner = THIS_MODULE,
.open = mychar_open,
.release = mychar_close,
.read = mychar_read,
.write = mychar_write,
.unlocked_ioctl = mychar_ioctl
};
int mychar_init(void)
{
int ret = 0;
dev_t devno = MKDEV(major, minor);
/* 申请设备号 */
ret = register_chrdev_region(devno, mychar_num, "mychar");
if (ret) {
ret = alloc_chrdev_region(&devno, minor, mychar_num, "mychar");
if (ret) {
printk("get devno failed\n");
return -1;
}
major = MAJOR(devno); // 容易遗漏，注意
}
/* 给struct cdev对象指定操作函数集 */
cdev_init(&gmydev.mydev, &myops);
/* 将 struct cdev对象添加到内核对应的数据结构里 */
gmydev.mydev.owner = THIS_MODULE;
cdev_add(&gmydev.mydev, devno, 1);
//初始化队列
init_waitqueue_head(&(gmydev.rq));
init_waitqueue_head(&(gmydev.wq));
return 0;
}
void __exit mychar_exit(void)
{
dev_t devno = MKDEV(major, minor);
cdev_del(&gmydev.mydev);
unregister_chrdev_region(devno, mychar_num);
}
//表示支持GPL的开源协议
MODULE_LICENSE("GPL");
module_init(mychar_init);
module_exit(mychar_exit);
mychar.h
#ifndef MY_CHAR_H
#define MY_CHAR_H
#include <asm/ioctl.h>
#define MY_CHAR_MAGIC 'k'
#define MYCHAR_IOCTL_GET_MAXLEN _IOR(MY_CHAR_MAGIC,1,int*)
#define MYCHAR_IOCTL_GET_CURLEN _IOR(MY_CHAR_MAGIC,2,int*)
#endif
testmychar_nonblockread.c
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include "mychar.h"
#include <stdio.h>
int main(int argc,char *argv[])
{
int fd = -1;
char buf[8] = "";
int ret = 0;
if(argc < 2)
{
printf("The argument is too few\n");
return 1;
}
fd = open(argv[1],O_RDWR); // | O_NONBLOCK);
if(fd < 0)
{
printf("open %s failed\n",argv[1]);
return 2;
}
ret = read(fd,buf,8);
if(ret < 0)
{
printf("read data failed\n");
}
else
{
printf("buf=%s\n",buf);
}
close(fd);
fd = -1;
return 0;
}
Makfile
ifeq ($(KERNELRELEASE),)
ifeq ($(ARCH),arm)
KERNELDIR ?= /home/linux/Linux_4412/kernel/linux-3.14
ROOTFS ?= /opt/4412/rootfs
else
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
endif
PWD := $(shell pwd)
modules:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
modules_install:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules INSTALL_MOD_PATH=$(ROOTFS) modules_install
clean:
rm -rf *.o *.ko .*.cmd *.mod.* modules.order Module.symvers .tmp_versions
else
CONFIG_MODULE_SIG=n
obj-m += mychar.o
endif
移除并新增内核模块
添加设备
非阻塞读执行效果：
阻塞读效果
