Linux内核编程之完成接口completion的简单使用
这里对完成接口completion如何实现不做深入解释，有兴趣的可以去看Linux源代码，主要在
- include/linux/completion.h
这个头文件里。这里只对如何使用结合demo稍作解释。下面直接给出驱动源代码：
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>
#include <linux/timer.h> // for timer_list API
#include <linux/param.h> // for HZ
#include <linux/jiffies.h> // for jiffies
#include <linux/interrupt.h>
#include <linux/completion.h>
#include <linux/miscdevice.h>
#include <linux/uaccess.h>
#include <linux/fs.h>
#include <linux/errno.h>
DECLARE_COMPLETION(completion_demo);//定义一个completion变量
static char completion_str[16] = {0x0};
static int completion_open(struct inode *inode, struct file *file) {
printk("completion opened.\n");
return 0;
}
static int completion_release(struct inode *inode, struct file *file) {
printk("completion released.\n");
return 0;
}
static ssize_t completion_read(struct file *file, char __user *buffer, size_t count, loff_t *pos) {
ssize_t ret;
printk("completion read.\n");
wait_for_completion_interruptible(&completion_demo);//阻塞在这儿
if (ret == 0) {
return count;
} else {
return -EFAULT;
}
}
static ssize_t completion_write(struct file *file, const char __user *buffer, size_t count, loff_t *pos) {
ssize_t ret;
printk("completion write.\n");
ret = copy_from_user(completion_str, buffer, count);
if (ret == 0) {
complete(&completion_demo);//唤醒阻塞的进程
return count;
} else {
return -EFAULT;
}
}
static struct file_operations completion_fops =
{
.owner = THIS_MODULE,
.open = completion_open,
.release = completion_release,
.read = completion_read,
.write = completion_write,
};
static struct miscdevice completion_dev = {
.minor = MISC_DYNAMIC_MINOR,
.name = "completion",
.fops = &completion_fops,
};
static int __init completion_demo_init(void)
{
int ret;
printk("init completion demo.\n");
ret = misc_register(&completion_dev);
if (ret) {
printk("misc_register error.\n");
return ret;
}
return 0;
}
static void __exit completion_demo_exit(void)
{
printk("exit completion demo.\n");
misc_deregister(&completion_dev);
}
MODULE_LICENSE("GPL");
MODULE_AUTHOR("zhuqinggooogle@gmail.com");
module_init(completion_demo_init);
module_exit(completion_demo_exit);
这里主要模拟这种情况：
- 两个进程，一个进程写，另一个进程读。但是，必须保证在一个进程写完后，另一个进程才能读
为此，我写了个简单的上层demo，下面是源代码：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
char completion_demo[] = "completion demo";
int main(int argc, char **argv) {
int fd = -1;
char buffer[16] = {0x0};
int ret;
pid_t pid;
pid = fork();
if (pid < 0) {
perror("fork error.\n");
exit(-1);
} else if (0 == pid) {
printf("----child process----\n");
fd = open("/dev/completion", O_RDWR);
if (fd < 0) {
perror("open error\n");
exit(-1);
}
ret = read(fd, buffer, 16);
if (ret > 0) {
printf("%s\n", buffer);
close(fd);
exit(0);
}
close(fd);
} else if (pid > 0) {
printf("----father process----\n");
fd = open("/dev/completion", O_RDWR);
if (fd < 0) {
perror("open error\n");
exit(-1);
}
printf("sleep for 10s just for delaying write operation.\n");
sleep(10);
ret = write(fd, completion_demo, sizeof(completion_demo));
if (ret > 0) {
printf("write ok.\n");
close(fd);
exit(0);
}
close(fd);
}
}
这里，父进程写，子进程读。父进程里休眠的10秒来模拟写延时的情况，子进程先读，读不到阻塞，然后父进程完成写操作后唤醒子进程。
我们编译驱动demo和上层demo，下面是驱动demo的Makefile：
LINUXROOT := /home/Hi3520D_SDK_V1.0.2.0/osdrv/kernel/linux-3.0.y
PWD := $(shell pwd)
obj-m := completion_demo.o
completion_demo-y += completion.o
default:
@make -C $(LINUXROOT) M=$(PWD) modules
clean:
@rm *.o *.ko -rf
@make -C $(LINUXROOT) M=$(PWD) clean
编译成功后，加载到开发板是看看：
/mnt/3520d $ insmod completion_demo.ko
init completion demo.
然后再去运行上层demo：
/mnt/3520d $ ./demo
----father procecompletion opened.
ss----
sleep focompletion opened.
r 10s just for dcompletion read.
elaying write operation.
----child process----
completion write.
write ok.
completion released.
/mnt/3520d $ completion released.
completion demo
看上去打印好乱，其实这是因为驱动demo里和上层demo里都有打印，打印混乱的结果。如果没有混乱应该是下面的情况：
/mnt/3520d $ ./demo
----father process----
completion opened.
sleep for 10s just for delaying write operation.
----child process----
completion opened.
completion read.
completion write.
write ok.
completion released.
completion demo
/mnt/3520d $ completion released.
