misc设备，内核态记录文件

1，kernel

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/types.h>
#include <linux/spinlock.h>
#include <linux/blkdev.h>
#include <linux/module.h> 
#include <linux/fs.h> 
#include <linux/errno.h> 
#include <linux/mm.h> 
#include <linux/cdev.h> 
#include <linux/miscdevice.h>
     
#define MISC_NAME   "miscdriver"

#define IO_CMD_LEN      1024  

typedef struct 
{
    int file_id; //todo
    int rw_pos;  //todo
    int cmd_type;
    int buff_len;
    char io_buff[IO_CMD_LEN - 16];
}KLOG_CMD_INFO;

#if 1

struct file *klog_fp = NULL;
loff_t klog_pos = 0;

static int user_cmd_proc(char *user_cmd, char *out_str)
{
    KLOG_CMD_INFO *klog_cmd = (KLOG_CMD_INFO *)user_cmd;
    KLOG_CMD_INFO *klog_ack = (KLOG_CMD_INFO *)out_str;
    
    if(klog_cmd->cmd_type == 1) { //open file
        if (klog_fp != NULL)  filp_close(klog_fp, NULL);
            
        klog_fp = filp_open(klog_cmd->io_buff, O_RDWR | O_CREAT | O_TRUNC, 0644);
        if (IS_ERR(klog_fp)){
            printk("filp_open error 
");
            return -1;
        }
        klog_pos = 0;
        sprintf(klog_ack->io_buff, "filp_open ok
");
    }
    
    if(klog_cmd->cmd_type == 2) { //write file
        mm_segment_t old_fs;
        old_fs = get_fs();
        set_fs(KERNEL_DS); //to check why
        klog_pos += vfs_write(klog_fp, klog_cmd->io_buff, klog_cmd->buff_len, &klog_pos);
        set_fs(old_fs);
        sprintf(klog_ack->io_buff, "vfs_write ok
");
    }

    if(klog_cmd->cmd_type == 3) { //close file
        filp_close(klog_fp, NULL);
        klog_fp = NULL;
        sprintf(klog_ack->io_buff, "filp_close ok
");
    }
    
    return 0;
}
#endif

char user_cmd[IO_CMD_LEN] = {0};
char out_str[IO_CMD_LEN] = {0};
 
static int misc_open(struct inode *inode, struct file *file)
{
    printk("misc_open
");
    return 0;
}
 
static int misc_ioctl( struct file *file, unsigned int cmd, unsigned long arg)
{    
    printk("misc_ioctl: %d 
", cmd);    
    
    if(copy_from_user(user_cmd,  (int *)arg, IO_CMD_LEN)) 
        return -EFAULT;
    
    user_cmd_proc(user_cmd, out_str);
    
    if(copy_to_user( (int *)arg, out_str, IO_CMD_LEN)) 
        return -EFAULT;

    return 0;
}

static ssize_t misc_write(struct file *filp, const char __user *buf, size_t size, loff_t *ppos)  
{
    int ret;
    
    if(IO_CMD_LEN <= size) return 0;

    if (copy_from_user(user_cmd, buf, size))  
        ret = - EFAULT;  

    user_cmd[size] = 0;
    printk(KERN_INFO "written %d bytes: %s
", size, user_cmd);  
    return 0;
}
 
static const struct file_operations misc_fops =
{
    .owner   =  THIS_MODULE,
    .open    =  misc_open,
    .write   =  misc_write,  
    .unlocked_ioctl = misc_ioctl,
};
 
static struct miscdevice misc_dev =
{
    .minor = MISC_DYNAMIC_MINOR,
    .name = MISC_NAME,
    .fops = &misc_fops,
};
 
 
static int __init misc_init(void)
{
    int ret;
     
    ret = misc_register(&misc_dev);
    if (ret)
    {
        printk("misc_register error
");
        return ret;
    }
 
    return 0;
}
 
static void __exit misc_exit(void)
{
    misc_deregister(&misc_dev);
}
 
module_init(misc_init);
module_exit(misc_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("derek");

2，app

#include <stdio.h>  
#include <fcntl.h>  
#include <stdlib.h>  
#include <string.h>  
#include <sys/types.h>  
#include <sys/stat.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <sys/syscall.h>

#define IO_CMD_LEN      1024  

typedef struct 
{
    int file_id; //todo
    int rw_pos;  //todo
    int cmd_type;
    int buff_len;
    char io_buff[IO_CMD_LEN - 16];
}KLOG_CMD_INFO;

KLOG_CMD_INFO cmd_info;

#if 0
int main()
{
    int fd;
    int ret = 0;

    fd = open("/dev/miscdriver", O_RDWR);
    if( fd < 0 ) {
        printf("open miscdriver WRONG！
");
        return 0;
    }

    sprintf(cmd_info.io_buff, "/home/derek/klog.txt");
    cmd_info.cmd_type = 1;
    ret = ioctl(fd, 0, &cmd_info);
    printf("open: ret=%d rdata:%s
", ret, cmd_info.io_buff);

    for(int i = 0; i < 10; i++) {
        sprintf(cmd_info.io_buff, "%d: ==============================
", i);
        cmd_info.buff_len = strlen(cmd_info.io_buff);
        cmd_info.cmd_type = 2;
        ret = ioctl(fd, 0, &cmd_info);
        printf("read: ret=%d rdata:%s
", ret, cmd_info.io_buff);
    }

    cmd_info.cmd_type = 3;
    ret = ioctl(fd, 0, &cmd_info);
    printf("close: ret=%d rdata:%s
", ret, cmd_info.io_buff);
   
    close(fd);
    return 0;
}
#else

int main()
{
    int fd;
    int ret = 0;
    char buf[]="this is a example for character devices driver by derek!";

    fd = open("/dev/miscdriver", O_RDWR);
    if( fd < 0 ) {
        printf("open miscdriver WRONG！
");
        return 0;
    }

    ret = write(fd, buf, sizeof(buf));
    printf("write: ret=%d 
", ret);
   
    close(fd);
    return 0;
}

#endif