linux环形缓冲区kfifo实践4：异步通知fasync

千册2023-08-11 12:22

基础知识

异步通知在内核中使用struct fasync_struct数据结构来描述。

cpp 复制代码 
<include/linux/fs.h>
struct fasync_struct {
	spinlock_t		fa_lock;
	int			magic;
	int			fa_fd;
	struct fasync_struct	*fa_next; /* singly linked list */
	struct file		*fa_file;
	struct rcu_head		fa_rcu;
};

设备驱动的file_operations的操作方法集中有一个fasync的方法，我们需要实现它。

cpp 复制代码 
static const struct file_operations demodrv_fops = {
    .owner = THIS_MODULE,
    ....
    fasync = my_fasync,
};

static int my_fasync(int fd, struct file *file, int on){
    struct mydemo_private_data *data = file->private_data;
    struct mydemo_device *device = data->device;
    return fasync_helper(fd, file, on, &device->fasync);
}

这里直接使用fasync_helper()函数来构造struct fasync_struct类型的节点，并添加到系统的链表中。

发送信号 kill_fasync

cpp 复制代码 
/* can be called from interrupts */
extern void kill_fasync(struct fasync_struct **, int, int);

sigaction

cpp 复制代码 
        struct sigaction {
               void     (*sa_handler)(int);
               void     (*sa_sigaction)(int, siginfo_t *, void *);
               sigset_t   sa_mask;
               int        sa_flags;
               void     (*sa_restorer)(void);
           };

struct sigaction act,oldact;

sigemptyset(&act.sa_mask);

sigaddset(&act.sa_mask,SIGIO);//设置SIGIO信号

act.sa_flags = SA_SIGINFO;//该选项可以使内核通过siginfo->si_band将POLL_IN和POLL_OUT上传到用户空间。便于在信号处理函数中区分读写信号。

驱动代码：

cpp 复制代码 
#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/types.h>
#include <linux/miscdevice.h>
#include <linux/kfifo.h>
#include <linux/wait.h>
#include <linux/poll.h>
#include <linux/mutex.h>

#define DEBUG_INFO(format, ...) printk("%s:%d -- "format"\n",\
__func__,__LINE__,##__VA_ARGS__)

struct ch5_kfifo_struct{
    struct miscdevice misc;
    struct file_operations fops;
    struct kfifo fifo;
    char buf[64];
    char name[64];
    wait_queue_head_t read_queue;
    wait_queue_head_t write_queue;
    struct fasync_struct *fasync;
};

static int ch5_open (struct inode *inode, struct file *file){
    struct ch5_kfifo_struct *p = (struct ch5_kfifo_struct *)container_of(file->f_op,struct ch5_kfifo_struct,fops);
    file->private_data = p;
    DEBUG_INFO("major = %d, minor = %d\n",MAJOR(inode->i_rdev),MINOR(inode->i_rdev));
    DEBUG_INFO("name = %s",p->misc.name);
    return 0;
}



static unsigned int ch5_poll(struct file *file, poll_table *wait){
    int mask = 0;
    struct ch5_kfifo_struct *p __attribute__((unused)) = (struct ch5_kfifo_struct *)file->private_data;
    DEBUG_INFO("begin wait:%s",p->name);
    poll_wait(file, &p->read_queue, wait);
    poll_wait(file, &p->write_queue, wait);
    DEBUG_INFO("poll:%s",p->name);
    if (!kfifo_is_empty(&p->fifo)){
        mask |= POLLIN | POLLRDNORM;
        DEBUG_INFO("POLLIN:%s",p->name);
    }
        
    if (!kfifo_is_full(&p->fifo)){
        mask |= POLLOUT | POLLWRNORM;
        DEBUG_INFO("POLLOUT:%s",p->name);
    }
        
    return mask;
}

static int ch5_fasync(int fd, struct file *file, int on){
    struct ch5_kfifo_struct *p = (struct ch5_kfifo_struct *)file->private_data;
    return fasync_helper(fd, file, on, &p->fasync);
}

static ssize_t ch5_read (struct file *file, char __user *buf, size_t size, loff_t *pos){
    struct ch5_kfifo_struct *p __attribute__((unused)) = (struct ch5_kfifo_struct *)file->private_data;
    int ret;
    int actual_readed = 0;

    if(kfifo_is_empty(&p->fifo)){
        if(file->f_flags & O_NONBLOCK){
            DEBUG_INFO("kfifo is null");
            return -EAGAIN;
        }
        ret = wait_event_interruptible(p->read_queue,kfifo_is_empty(&p->fifo) == 0);
        if(ret){
            DEBUG_INFO("wait_event_interruptible error");
            return ret;
        }
        DEBUG_INFO("");
    }
    
    ret = kfifo_to_user(&p->fifo, buf, size, &actual_readed);
    if (ret){
        DEBUG_INFO("kfifo_to_user error");
		return -EIO;
    }
    
    DEBUG_INFO("size = %d,actual_readed = %d\n",size,actual_readed);

    if (!kfifo_is_full(&p->fifo)){
        wake_up_interruptible(&p->write_queue);
        if(p->fasync != NULL){
            kill_fasync(&p->fasync, SIGIO, POLL_OUT);
        }
    }

    memset(p->buf,0,sizeof(p->buf));
    ret = copy_from_user(p->buf, buf, actual_readed);
    if(ret != 0){
        DEBUG_INFO("copy_from_user error ret = %d\n",ret);
    }else{
        DEBUG_INFO("read p->buf = %s\n",p->buf);
    }
    *pos = *pos + actual_readed;
    return actual_readed;
}
static ssize_t ch5_write (struct file *file, const char __user *buf, size_t size, loff_t* pos){
    struct ch5_kfifo_struct *p = (struct ch5_kfifo_struct *)file->private_data;
    int actual_writed = 0;
    int ret;
    if(kfifo_is_full(&p->fifo)){
        if(file->f_flags & O_NONBLOCK){
            DEBUG_INFO("kfifo is full");
            return -EAGAIN;
        }
        ret = wait_event_interruptible(p->write_queue, kfifo_is_full(&p->fifo) == 0);
        if(ret){
            DEBUG_INFO("wait_event_interruptible error");
            return ret;
        }
        DEBUG_INFO("");
    }
    ret = kfifo_from_user(&p->fifo, buf, size, &actual_writed);
    if (ret){
        DEBUG_INFO("kfifo_from_user error");
		return -EIO;
    }
    
    DEBUG_INFO("actual_writed = %d\n",actual_writed);

    if (!kfifo_is_empty(&p->fifo)){
        wake_up_interruptible(&p->read_queue);
        if(p->fasync != NULL){
            kill_fasync(&p->fasync, SIGIO, POLL_IN);
        }
        
    }
    memset(p->buf,0,sizeof(p->buf));
    ret = copy_from_user(p->buf, buf, actual_writed);
    if(ret != 0){
        DEBUG_INFO("copy_from_user error ret = %d\n",ret);
    }else{
        DEBUG_INFO("write:p->buf = %s\n",p->buf);
    }
    *pos = *pos + actual_writed;
    return actual_writed;
}

static int ch5_release (struct inode *inode, struct file *file){
    struct ch5_kfifo_struct *p = (struct ch5_kfifo_struct *)container_of(file->f_op,struct ch5_kfifo_struct,fops);
    ch5_fasync(-1, file, 0);
    p->fasync = NULL;
    DEBUG_INFO("close");
    return 0;
}
struct ch5_kfifo_struct ch5_kfifo[1];
//  = {
//     .misc = { 
//         .name = "ch5-04-block",
//         .minor = MISC_DYNAMIC_MINOR,
//     },
//     .fops = {
//         .owner = THIS_MODULE,
//         .read = ch5_read,
//         .write = ch5_write,
//         .open = ch5_open,
//         .release = ch5_release,
//     },
// };

static int __init ch5_init(void){
    int ret = 0;
    int i = 0;
    struct ch5_kfifo_struct *p;

    DEBUG_INFO("start init\n");
    for(i = 0;i < sizeof(ch5_kfifo)/sizeof(ch5_kfifo[0]);i++){
        p = &ch5_kfifo[i];
        p->fasync = NULL;
        snprintf(p->name,sizeof(p->name),"ch5-06-fasync-%d",i);
        p->misc.name = p->name;
        p->misc.minor = MISC_DYNAMIC_MINOR;

        p->fops.owner = THIS_MODULE;
        p->fops.read = ch5_read;
        p->fops.write = ch5_write;
        p->fops.open = ch5_open;
        p->fops.release = ch5_release;
        p->fops.poll = ch5_poll;
        p->fops.fasync = ch5_fasync;

        p->misc.fops = &p->fops;
        ret = kfifo_alloc(&p->fifo,
                    8,
                    GFP_KERNEL);
        if (ret) {
            DEBUG_INFO("kfifo_alloc error: %d\n", ret);
            ret = -ENOMEM;
            return ret;
        }
        DEBUG_INFO("kfifo_alloc size = %d",kfifo_avail(&p->fifo));

        init_waitqueue_head(&p->read_queue);
        init_waitqueue_head(&p->write_queue);

        ret = misc_register(&p->misc);
        if(ret < 0){
            DEBUG_INFO("misc_register error: %d\n", ret);
            return ret;
        }
    }
    
    DEBUG_INFO("misc_register ok");
    return 0;
}

static void __exit ch5_exit(void){
    int i = 0;
    struct ch5_kfifo_struct *p;
    for(i = 0;i < sizeof(ch5_kfifo)/sizeof(ch5_kfifo[0]);i++){
        p = &ch5_kfifo[i];
        misc_deregister(&p->misc);
        kfifo_free(&p->fifo);
    }

    DEBUG_INFO("exit\n");
}

module_init(ch5_init);
module_exit(ch5_exit);

MODULE_LICENSE("GPL");

应用代码：

cpp 复制代码 
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <errno.h>
#include <poll.h>
#include <linux/input.h>
#include <unistd.h>
#include <signal.h>
#include <sys/ioctl.h>

#define DEBUG_INFO(format, ...) printf("%s:%d -- "format"\n",\
    __func__,__LINE__,##__VA_ARGS__)

int fd = 0;

void signal_handler(int signum,siginfo_t *siginfo,void *act){
    int ret = 0;
    char buf[1024] = {0};
    if(signum == SIGIO){
        if(siginfo->si_band & POLLIN){
            DEBUG_INFO("kfifo is not empty");
            if((ret = read(fd,buf,sizeof(buf))) == -1){
                buf[ret] = '\0';
            }
            DEBUG_INFO("buf = %s",buf);
        }
        if(siginfo->si_band & POLLOUT){
            DEBUG_INFO("kfifo is not full");
        }
    }
}

int main(int argc, char**argv){
    struct sigaction act,oldact;
    int flag;
    char *filename = "/dev/ch5-06-fasync-0";
    int ret = 0;
    sigemptyset(&act.sa_mask);
    sigaddset(&act.sa_mask,SIGIO);

    act.sa_flags = SA_SIGINFO;
    act.sa_sigaction = signal_handler;

    if(sigaction(SIGIO, &act,&oldact) == -1){
        DEBUG_INFO("sigaction failed");
        return -1;
    }
    fd = open(filename,O_RDWR);
    if(fd < 0){
        perror("open");
        DEBUG_INFO("open %s failed",filename);
        return -1;
    }
    DEBUG_INFO("open %s ok",filename);

    ret = fcntl(fd, F_SETOWN, getpid());
    if(ret < 0){
        DEBUG_INFO("fcntl F_SETOWN  %s failed",filename);
        return -1;
    }
    ret = fcntl(fd, F_SETSIG, SIGIO);
    if(ret < 0){
        DEBUG_INFO("fcntl F_SETSIG  %s failed",filename);
        return -1;
    }
    flag = fcntl(fd, F_GETFL);
    ret = fcntl(fd, F_SETFL, flag | FASYNC);
    if(ret < 0){
        DEBUG_INFO("fcntl F_SETFL  %s failed",filename);
        return -1;
    }
    while(1){
        sleep(1);
    }              
    return 0;
}

测试结果：

小结

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