非阻塞 IO(NIO)
文章目录
- 非阻塞 IO(NIO)
-
- 模型
- 驱动程序
- 应用程序
- 模块使用
非阻塞 IO(NIO)
上一节中 https://blog.csdn.net/tyustli/article/details/135140523，使用等待队列头实现了阻塞 IO
程序使用时，阻塞 IO 和非阻塞 IO 的区别在于文件打开的时候是否使用了
O_NONBLOCK 标志位。
- O_RDWR 默认以阻塞的方式打开
- O_NONBLOCK 以非阻塞的方式打开
模型
驱动程序
文件打卡时，文件打开标志存放在文件结构体 struct file f_flags 字段
文件结构体原型在 linux/fs.h 文件中
struct file {
union {
struct llist_node f_llist;
struct rcu_head f_rcuhead;
unsigned int f_iocb_flags;
};
/*
* Protects f_ep, f_flags.
* Must not be taken from IRQ context.
*/
spinlock_t f_lock;
fmode_t f_mode;
atomic_long_t f_count;
struct mutex f_pos_lock;
loff_t f_pos;
unsigned int f_flags;
struct fown_struct f_owner;
const struct cred *f_cred;
struct file_ra_state f_ra;
struct path f_path;
struct inode *f_inode; /* cached value */
const struct file_operations *f_op;
u64 f_version;
#ifdef CONFIG_SECURITY
void *f_security;
#endif
/* needed for tty driver, and maybe others */
void *private_data;
#ifdef CONFIG_EPOLL
/* Used by fs/eventpoll.c to link all the hooks to this file */
struct hlist_head *f_ep;
#endif /* #ifdef CONFIG_EPOLL */
struct address_space *f_mapping;
errseq_t f_wb_err;
errseq_t f_sb_err; /* for syncfs */
} __randomize_layout
__attribute__((aligned(4))); /* lest something weird decides that 2 is OK */
所以驱动中需要判断文件打开标志是否支持非阻塞方式
new_chrdev_t *dev = (new_chrdev_t *)file->private_data;
if (file->f_flags & O_NONBLOCK) {
if (!dev->flag) {
return -EAGAIN;
}
}
驱动程序源码
#include "asm-generic/errno-base.h"
#include "linux/device/class.h"
#include "linux/export.h"
#include "linux/uaccess.h"
#include 应用程序
打开文件时使用 O_NONBLOCK 非阻塞方式打开文件
fd = open(filename, O_RDWR | O_NONBLOCK);
如果文件读取失败，循环读取
retvalue = -1;
while (retvalue < 0) {
retvalue = read(fd, readbuf, 50);
if (retvalue < 0) {
printf("u: read file %s failed!\r\n", filename);
sleep(3);
} else {
/* 读取成功，打印出读取成功的数据 */
printf("u: read data:%s\r\n", readbuf);
}
}
完整应用程序代码
#include "stdio.h"
#include "unistd.h"
#include "sys/types.h"
#include "sys/stat.h"
#include "fcntl.h"
#include "stdlib.h"
#include "string.h"
static char usrdata[] = { "user data!" };
int main(int argc, char *argv[])
{
int fd, retvalue;
char *filename;
char readbuf[100], writebuf[100];
if (argc != 3) {
printf("u: error Usage!\r\n");
return -1;
}
filename = argv[1];
/* 打开驱动文件 */
fd = open(filename, O_RDWR | O_NONBLOCK);
if (fd < 0) {
printf("u: can't open file %s\r\n", filename);
return -1;
}
/* 从驱动 文件读取数据 */
if (atoi(argv[2]) == 1) {
retvalue = -1;
while (retvalue < 0) {
retvalue = read(fd, readbuf, 50);
if (retvalue < 0) {
printf("u: read file %s failed!\r\n", filename);
sleep(3);
} else {
/* 读取成功，打印出读取成功的数据 */
printf("u: read data:%s\r\n", readbuf);
}
}
}
/* 向设备驱动写数据 */
if (atoi(argv[2]) == 2) {
memcpy(writebuf, usrdata, sizeof(usrdata));
retvalue = write(fd, writebuf, 50);
if (retvalue < 0) {
printf("u: write file %s failed!\r\n", filename);
}
}
/* 关闭设备 */
retvalue = close(fd);
if (retvalue < 0) {
printf("u: can't close file %s\r\n", filename);
return -1;
}
return 0;
}
模块使用
模块安装
modprobe my_module
查看设备节点
ls /dev
~ # ls /dev/
chr_test1 ptypc tty32 tty7
console ptypd tty33 tty8
cpu_dma_latency ptype tty34 tty9
full ptypf tty35 ttyAMA0
gpiochip0 random tty36 ttyAMA1
gpiochip1 root tty37 ttyAMA2
gpiochip2 rtc0 tty38 ttyAMA3
gpiochip3 snd tty39 ttyp0
hwrng tty tty4 ttyp1
模块使用
~ # /lib/modules/6.5.7+/my_app /dev/chr_test1 1 &
~ # k: chrdevbase open
u: read file /dev/chr_test1 failed!
u: read file /dev/chr_test1 failed!
~ # /lib/modules/6.5.7+/my_app /dev/chr_test1 2
k: chrdevbase open
k: write data success write data is: user data!
k: chrdevbase release
~ # k: read data success
k: chrdevbase release
u: read data:kernel data this tyustli test
[1]+ Done /lib/modules/6.5.7+/my_app /dev/chr_test1 1
~ #