lv14 IO模型：阻塞和非阻塞 7

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 3int 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curlenmemcpy(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curlenpmydev->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) modulesmodules_install:$(MAKE) -C $(KERNELDIR) M=$(PWD) modules INSTALL_MOD_PATH=$(ROOTFS) modules_installclean:rm -rf  *.o  *.ko  .*.cmd  *.mod.*  modules.order  Module.symvers   .tmp_versionselse
CONFIG_MODULE_SIG=n
obj-m += mychar.oendif

移除并新增内核模块