一、五种IO模型------读写外设数据的方式
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阻塞: 不能操作就睡觉
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非阻塞:不能操作就返回错误
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多路复用:委托中介监控
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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
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异步IO:向内核注册操作请求,内核完成操作后发通知信号
二、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);
flags |= O_NONBLOCK;
fcntl(fd, F_SETFL, flags);
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
*/
示例:
mychar.h
#ifndef MY_CHAR_H
#define MY_CHAR_H#include <asm/ioctl.h>#define MY_CHAR_MAGIC 'c'#define MYCHAR_IOCTL_GET_MAXLEN _IOR(MY_CHAR_MAGIC, 1, int *)
#define MYCHAR_IOCTL_GET_CURLEN _IOR(MY_CHAR_MAGIC, 2, int *)#endif
mychar.c
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/wait.h>
#include <linux/sched.h>
#include <asm/uaccess.h>
#include <asm/ioctl.h>#include "mychar.h"#define BUF_LEN 100int major = 11; //主设备号
int minor = 0; //次设备号
int char_num = 1; //设备号数量struct mychar_dev
{struct cdev mydev;char mydev_buf[BUF_LEN];int curlen;wait_queue_head_t rq;wait_queue_head_t wq;
};
struct mychar_dev gmydev;int mychar_open (struct inode *pnode, struct file *pfile)//打开设备
{pfile->private_data = (void *) (container_of(pnode->i_cdev, struct mychar_dev, mydev));printk("open\n");return 0;
}int mychar_close(struct inode *pnode, struct file *pfile)//关闭设备
{printk("close\n");return 0;
}ssize_t mychar_read (struct file *pfile, char __user *puser, size_t count, loff_t *p_pos) {struct mychar_dev *pmydev = (struct mychar_dev *)pfile->private_data;int size = 0;int ret = 0;/* 判断是否有数据可读 */if(pmydev->curlen <= 0) {if(pfile->f_flags & O_NONBLOCK) { //非阻塞printk("O_NONBLOCK Not Data Read\n");return -1;} else { //阻塞/* 睡眠 当curlen>0 时返回 */ret = wait_event_interruptible(pmydev->rq, pmydev->curlen > 0);if(ret) {return -ERESTARTSYS;}}}// 确定要读取的数据长度,如果请求大于设备当前数据长度,则读取全部可用数据if (count > pmydev->curlen) {size = pmydev->curlen;}else {size = count;}// 将设备数据复制到用户空间缓冲区ret = copy_to_user(puser, pmydev->mydev_buf, size);if(ret) {printk("copy_to_user failed\n");return -1;}// 移动设备内部缓冲区,去除已读取的数据memcpy(pmydev->mydev_buf, pmydev->mydev_buf + size, pmydev->curlen - size);pmydev->curlen -= size;wake_up_interruptible(&pmydev->wq);// 返回实际读取的字节数return size;
}ssize_t mychar_write (struct file *pfile, const char __user *puser, size_t count, loff_t *p_pos) {struct mychar_dev *pmydev = (struct mychar_dev *)pfile->private_data;int size = 0;int ret = 0;if(pmydev->curlen >= BUF_LEN) {if(pfile->f_flags & O_NONBLOCK) { //非阻塞printk("O_NONBLOCK Can Not Write Data\n");return -1;} else { //阻塞ret = wait_event_interruptible(pmydev->wq, pmydev->curlen < BUF_LEN);if(ret) {return -ERESTARTSYS;}}}// 确定要写入的数据长度,如果请求大于设备缓冲区剩余空间,则写入剩余空间大小if (count > BUF_LEN - pmydev->curlen) {size = BUF_LEN - pmydev->curlen;}else {size = count;}// 从用户空间复制数据到设备缓冲区ret = copy_from_user(pmydev->mydev_buf + pmydev->curlen, puser, size);if(ret) {printk("copy_from_user failed\n");return -1;}// 更新设备缓冲区中的数据长度pmydev->curlen += size;/* 唤醒读阻塞 */wake_up_interruptible(&pmydev->rq);// 返回实际写入的字节数return size;
}long mychar_ioctl(struct file *pfile, unsigned int cmd, unsigned long arg)
{struct mychar_dev *pmydev = (struct mychar_dev *)pfile->private_data;int __user *pret = (int *)arg;int maxlen = BUF_LEN;int ret = 0;switch(cmd) {case MYCHAR_IOCTL_GET_MAXLEN:ret = copy_to_user(pret, &maxlen, sizeof(int));if(ret) {printk("copy_from_user failed\n");return -1;}break;case MYCHAR_IOCTL_GET_CURLEN:ret = copy_to_user(pret, &pmydev->curlen, sizeof(int));if(ret) {printk("copy_from_user failed\n");return -1;}break;default:printk("The is a know\n");return -1;}return 0;
}struct file_operations myops = {.owner = THIS_MODULE,.open = mychar_open,.read = mychar_read,.write = mychar_write,.unlocked_ioctl = mychar_ioctl,
};int __init mychar_init(void)
{int ret = 0;dev_t devno = MKDEV(major, minor);/* 手动申请设备号 */ret = register_chrdev_region(devno, char_num, "mychar");if (ret) {/* 动态申请设备号 */ret = alloc_chrdev_region(&devno, minor, char_num, "mychar");if(ret){printk("get devno failed\n");return -1;}/*申请成功 更新设备号*/major = MAJOR(devno);}/* 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中 */gmydev.mydev.owner = THIS_MODULE;cdev_add(&gmydev.mydev, devno, char_num);/* 初始化 */init_waitqueue_head(&gmydev.rq);init_waitqueue_head(&gmydev.wq);return 0;
}void __exit mychar_exit(void)
{dev_t devno = MKDEV(major, minor);printk("exit %d\n", devno);/* 从内核中移除一个字符设备 */cdev_del(&gmydev.mydev);/* 回收设备号 */unregister_chrdev_region(devno, char_num);}MODULE_LICENSE("GPL");
module_init(mychar_init);
module_exit(mychar_exit);
testmychar_blockwait.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <sys/ioctl.h>#include "mychar.h"
int main(int argc, char *argv[])
{int fd = -1;char buf[100];if(argc < 2) {printf("The argument is too few\n");return -1;}fd = open(argv[1], O_RDWR);if(fd < 0) {perror("open");return -1;}memset(buf, 'C', sizeof(buf));if ( (write(fd, buf, strlen(buf)) ) < 0 ) {printf("write failed\n");return -1;}close(fd);fd = -1;return 0;
}
testmychar_blockread.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <sys/ioctl.h>#include "mychar.h"
int main(int argc, char *argv[])
{int fd = -1;char buf[32] = "";int ret = 0;if(argc < 2) {printf("The argument is too few\n");return -1;}fd = open(argv[1], O_RDWR);if(fd < 0) {perror("open");return -1;}if ( (read(fd, buf, sizeof(buf)) ) < 0 ) {printf("read failed\n");return -1;} else {printf("buf = %s\n", buf);}close(fd);fd = -1;return 0;
}
运行结果: