东莞网站建设网络公司公司,wordpress简历页,企业管理六大体系,wordpress动图打开很慢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#xff1a;不能操作就返回错误(通过轮询即才能实现阻塞的情况 #xff09; 多路复用#xff1a;委托中介监控 信号驱动#xff1a;让内核如果能操作时发信号#xff0c;在信号处理函数中操作 异步IO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conditionC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_bufsize,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*)#endiftestmychar_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.hint 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_SIGn
obj-m mychar.oendif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
