高级字符驱动程序操作之异步通知IO（实践篇）

 

1. async.c 主要展示异步通知机制在驱动程序中的实现

 

#include <linux/module.h>
#include <linux/init.h>

#include <linux/fs.h>     /* everything... */
#include <linux/types.h>  /* size_t */
#include <linux/cdev.h>
#include <linux/fcntl.h>
#include <asm/uaccess.h> /* copy user */
#include <linux/poll.h> /* POLL_IN */

MODULE_AUTHOR("victorsummer");
MODULE_LICENSE("Dual BSD/GPL");


static int async_major = 0;
struct fasync_struct *async_queue;
static char *buffer = NULL;

ssize_t async_read (struct file *filp, char __user *buf, size_t count, loff_t *pos)
{
    if(buffer)
        copy_to_user(buf, buffer, count);

    return count;
}

ssize_t async_write (struct file *filp, const char __user *buf, size_t count,
        loff_t *pos)
{
    if(buffer)
        copy_from_user(buffer, buf, count);
    if(async_queue)
        kill_fasync(&async_queue, SIGIO, POLL_IN);
    return count;
}

static int async_fasync(int fd, struct file *filp, int mode)
{
    return fasync_helper(fd, filp, mode, &async_queue);
}

int async_release(struct inode *inode, struct file *filp)
{
    async_fasync(-1, filp, 0);
    return 0;
}

static int async_open(struct inode *inode, struct file *filp)
{
    return nonseekable_open(inode, filp);
}


struct file_operations async_fops = {
    .owner = THIS_MODULE,
    .read =  async_read,
    .write = async_write,
    .fasync = async_fasync,
    .release = async_release,
    .open = async_open,
};

int async_init(void)
{
    int result;
    dev_t dev = 0;

    struct cdev *async_cdev = cdev_alloc();

    if (async_major) {
        dev = MKDEV(async_major, 0);
        result = register_chrdev_region(dev, 1, "async");
    } else {
        result = alloc_chrdev_region(&dev, 0, 1, "async");
        async_major = MAJOR(dev);
    }
    if (result < 0) {
        return result;
    }

    if(!buffer)
        buffer = kmalloc(1024*sizeof(char), GFP_KERNEL);

    cdev_init(async_cdev, &async_fops);
    async_cdev->owner = THIS_MODULE;
    cdev_add(async_cdev, dev, 1);

    return 0;
}

void async_cleanup(void)
{
    dev_t devno;
    if(buffer)
    {
        kfree(buffer);
        buffer = NULL;
    }
    devno = MKDEV(async_major, 0);
    unregister_chrdev_region(devno, 1);
}

module_init(async_init);
module_exit(async_cleanup);

#include <linux/module.h> #include <linux/init.h> #include <linux/fs.h> /* everything... */ #include <linux/types.h> /* size_t */ #include <linux/cdev.h> #include <linux/fcntl.h> #include <asm/uaccess.h> /* copy user */ #include <linux/poll.h> /* POLL_IN */ MODULE_AUTHOR("victorsummer"); MODULE_LICENSE("Dual BSD/GPL"); static int async_major = 0; struct fasync_struct *async_queue; static char *buffer = NULL; ssize_t async_read (struct file *filp, char __user *buf, size_t count, loff_t *pos) { if(buffer) copy_to_user(buf, buffer, count); return count; } ssize_t async_write (struct file *filp, const char __user *buf, size_t count, loff_t *pos) { if(buffer) copy_from_user(buffer, buf, count); if(async_queue) kill_fasync(&async_queue, SIGIO, POLL_IN); return count; } static int async_fasync(int fd, struct file *filp, int mode) { return fasync_helper(fd, filp, mode, &async_queue); } int async_release(struct inode *inode, struct file *filp) { async_fasync(-1, filp, 0); return 0; } static int async_open(struct inode *inode, struct file *filp) { return nonseekable_open(inode, filp); } struct file_operations async_fops = { .owner = THIS_MODULE, .read = async_read, .write = async_write, .fasync = async_fasync, .release = async_release, .open = async_open, }; int async_init(void) { int result; dev_t dev = 0; struct cdev *async_cdev = cdev_alloc(); if (async_major) { dev = MKDEV(async_major, 0); result = register_chrdev_region(dev, 1, "async"); } else { result = alloc_chrdev_region(&dev, 0, 1, "async"); async_major = MAJOR(dev); } if (result < 0) { return result; } if(!buffer) buffer = kmalloc(1024*sizeof(char), GFP_KERNEL); cdev_init(async_cdev, &async_fops); async_cdev->owner = THIS_MODULE; cdev_add(async_cdev, dev, 1); return 0; } void async_cleanup(void) { dev_t devno; if(buffer) { kfree(buffer); buffer = NULL; } devno = MKDEV(async_major, 0); unregister_chrdev_region(devno, 1); } module_init(async_init); module_exit(async_cleanup);

 

 

2. Makefile

 

KERNELDIR = /usr/src/linux-headers-2.6.31-14-generic
PWD := $(shell pwd)

obj-m := async.o

modules:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules

KERNELDIR = /usr/src/linux-headers-2.6.31-14-generic PWD := $(shell pwd) obj-m := async.o modules: $(MAKE) -C $(KERNELDIR) M=$(PWD) modules

 

 

3. async_testr.c 异步读取程序

 

#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <signal.h>
#include <string.h>

int async_fd;
void sig_handler(int signo)
{
    int code;

        if (signo==SIGIO)
        {
        char *buf = malloc(30*sizeof(char));

        if ((code=read(async_fd, buf, 24)) == -1)
            printf("read err! code=%d /n", code);

        else
            printf("read ok! code=%d /n", code);
        printf("Read %s from async module /n", buf);
        free(buf);
        }
        return;
}

int main()
{
        struct sigaction action;

        memset(&action, 0, sizeof(action));
        action.sa_handler = sig_handler;
        action.sa_flags = 0;

    sigaction(SIGIO, &action, NULL);

    async_fd = open("/dev/async", O_RDONLY);
    fcntl(async_fd, F_SETOWN, getpid());
    fcntl(async_fd, F_SETFL, fcntl(STDIN_FILENO, F_GETFL) | FASYNC);

    while(1)
    {
            sleep(86400);
    }

    close(async_fd);
    exit(0);
}

#include <unistd.h> #include <sys/stat.h> #include <fcntl.h> #include <stdlib.h> #include <stdio.h> #include <signal.h> #include <string.h> int async_fd; void sig_handler(int signo) { int code; if (signo==SIGIO) { char *buf = malloc(30*sizeof(char)); if ((code=read(async_fd, buf, 24)) == -1) printf("read err! code=%d /n", code); else printf("read ok! code=%d /n", code); printf("Read %s from async module /n", buf); free(buf); } return; } int main() { struct sigaction action; memset(&action, 0, sizeof(action)); action.sa_handler = sig_handler; action.sa_flags = 0; sigaction(SIGIO, &action, NULL); async_fd = open("/dev/async", O_RDONLY); fcntl(async_fd, F_SETOWN, getpid()); fcntl(async_fd, F_SETFL, fcntl(STDIN_FILENO, F_GETFL) | FASYNC); while(1) { sleep(86400); } close(async_fd); exit(0); }

 

 

4. async_testw.c 写入程序

 

#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>

int main()
{
    char *write_buffer = "Hello, Character driver!";

    int async_fd;

    int code;



    async_fd = open("/dev/async",O_WRONLY );



    while(*write_buffer != '/0')
    {
        code = write(async_fd , write_buffer , 24);
        printf("Write %d bytes to async_fd/n", code);
        write_buffer += code;
    }

    close(async_fd);

    exit(0);
}

#include <unistd.h> #include <sys/stat.h> #include <fcntl.h> #include <stdlib.h> #include <stdio.h> int main() { char *write_buffer = "Hello, Character driver!"; int async_fd; int code; async_fd = open("/dev/async",O_WRONLY ); while(*write_buffer != '/0') { code = write(async_fd , write_buffer , 24); printf("Write %d bytes to async_fd/n", code); write_buffer += code; } close(async_fd); exit(0); }

 

 

5. Makefile

 

all : async_testw.o async_testr.o
        gcc -o async_testw.o async_testw.c
        gcc -o async_testr.o async_testr.c

all : async_testw.o async_testr.o gcc -o async_testw.o async_testw.c gcc -o async_testr.o async_testr.c

 

 

6. 开始测试

 

装载驱动程序

sudo insmod ./async.ko

查看主设备号，假设为250

cat /proc/devices

建立设备节点

sudo mknod /dev/async c 250 0

更改权限

sudo chgrp staff /dev/async

sudo chmod 664 /dev/async

 

在终端1中打开异步读取程序，程序开始sleep

sudo ./async_testr.o

在终端2中打开写入程序

sudo ./async_testw.o

 

结果：

终端2打印：

Write 24 bytes to async_fd

终端1打印：

read ok! code=24
Read Hello, Character driver! from async module