錯誤地傳遞參數？ C問題

Question

當我的TimerExpire函數在計時器結束時最終調用時，它會打印出亂碼。有人知道爲什麼但我在IOCTL_MAKE_TIMER中的printk函數正確打印出來，所以我認爲這是因爲我錯誤地傳遞了數據。通過在第一個參數中設置計時器，告訴它調用第二個參數指定的函數，並將數據（這是第三個參數）傳遞給該函數，setup_timer（）工作。

在我的情況下，它調用TimerExpire（char * data）函數，傳遞給它的final_arg，它是一個char *到kern_arg。我甚至嘗試將kern_arg直接傳遞給函數......也給了我胡言亂語。

以前（昨天），我有char * kern_arg，而不是char kern_arg []，並且完美解決，但我認爲這是不安全的。

如果有人可以提供一些見解，那將是驚人的！謝謝！

//Necessary Includes For Device Drivers. 
#include <linux/init.h> 
#include <linux/module.h> 
#include <linux/kernel.h> 
#include <linux/fs.h> 
#include <linux/errno.h> 
#include <linux/proc_fs.h> 
#include <asm/uaccess.h> 
#include <linux/timer.h> 
#include <linux/ioctl.h> 

#define DEVICE_NAME "mytimer" 
#define DEVICE_FILE_NAME "mytimer" 
#define MAJOR_NUM 61 
#define MINOR_NUM 0 
#define SUCCESS 0 
#define IOCTL_MAKE_TIMER _IOWR(MAJOR_NUM, 0, int) 
#define IOCTL_SET_TIMER _IOWR(MAJOR_NUM, 1, int) 
#define IOCTL_GET_TIMER _IOWR(MAJOR_NUM, 2, int) 


//Module License 
MODULE_LICENSE("Dual BSD/GPL"); 

//Initialize timer structure. 
static struct timer_list my_timer; 

//Forward Declarations for File Operation Functions and Other Functions. 
static int mytimer_open(struct inode *inode, struct file *file); 
static int mytimer_release(struct inode *inode, struct file *file); 
int mytimer_ioctl(struct inode *inode, struct file *file, unsigned int ioctl_num, unsigned long args); 
void TimerExpire(char* data); 

//Syscall Operations for the module. 
struct file_operations FileOps = 
{ 
    .owner = THIS_MODULE, 
    .open = mytimer_open, 
    .release = mytimer_release, 
    .ioctl = mytimer_ioctl 
}; 

//Syscall function for opening the module. 
static int mytimer_open(struct inode *inode, struct file *file) 
{ 
    try_module_get(THIS_MODULE); 

    return SUCCESS; 
} 

//Syscall function for releasing the module. 
static int mytimer_release(struct inode *inode, struct file *file) 
{ 
    module_put(THIS_MODULE); 

    return SUCCESS; 
} 

//Syscall function for controlling the module through IOCTLs. 
int mytimer_ioctl(struct inode *inode, struct file *file, unsigned int fcn, unsigned long args) 
{ 
    //Copies the function parameters from userspace to kernel space in order to use them in the kernel module. 
    char* user_arg = args; 
    char kern_arg[strlen_user(user_arg)]; 
    copy_from_user(kern_arg, user_arg, strlen_user(user_arg)); 
    char* final_arg = kern_arg; 

    //If there is a timer, and the command is to make a new one, the old timer will be removed so a new one can be setup. 
    if (timer_pending(&my_timer) && fcn == IOCTL_MAKE_TIMER) 
{ 
    del_timer_sync(&my_timer); 
    printk("Timer already exists. Deleting old timer and setting new timer.\n"); 
} 

//Switch function that serves the function that is called. 
//Note that the make and set timer functions are separate. This is because only 1 arg is passed via ioctl at a time, so I had to make two different ioctl calls. 
switch (fcn) 
{ 
    //Make a new timer. 
    case IOCTL_MAKE_TIMER: 
     setup_timer(&my_timer, TimerExpire, final_arg); 
     printk("Made timer with message: %s\n", final_arg); 
     break; 

    //Set the timer made above. 
    case IOCTL_SET_TIMER:   
     mod_timer(&my_timer, jiffies + msecs_to_jiffies(args * 1000)); 
     printk("Armed timer for %d seconds.\n", args); 
     break; 

    //Print the current timer, if any. 
    case IOCTL_GET_TIMER: 
     if (!timer_pending(&my_timer)) 
     { 
      printk("No timer currently set.\n"); 
     }   
     else 
     { 
      printk("Time left in timer: %u seconds\n", jiffies_to_msecs(my_timer.expires - jiffies)/1000); 
      printk("Message in timer is: %s\n", my_timer.data); 
     } 
     break; 
} 

return SUCCESS; 
} 


//Function to perform when timer expires. 
void TimerExpire(char* data) 
{ 
    printk("%s\n", data); 
} 

//Module Init and Exit Functions. 
int init_module(void) 
{ 
printk("Loading MyTimer Kernel Module...\n"); 
    //Register the device with the system to obtain the major number and register the file operations for syscall functionality. 
int initResult = register_chrdev(MAJOR_NUM, "mytimer", &FileOps); 

    //If we couldn't register the device, print the error. 
    if (initResult < 0) 
    { 
    printk("Cannot obtain major number %d\n", MAJOR_NUM); 

    return initResult; 
    } 

    printk("Please create device file using:\n\tmknod /dev/mytimer c 61 0\n"); 

    return SUCCESS; 
} 
void cleanup_module(void) 
{ 
    //Unregister the device with the system to free the major number. 
    printk("Unloading MyTimer Kernel Module...\n"); 
    unregister_chrdev(MAJOR_NUM, "mytimer"); 
    printk("MyTimer Kernel Module Unloaded.\n"); 
} 

Answer 1

在這種代碼，ioctl(fd,IOCTL_MAKE_TIMER,...)呼叫傳遞setup_timer()一個指向位於內核棧上的陣列，然後返回。由於定時器到期，用於保存該數組的內存可能已被重用。

您需要保持內存，直到計時器到期。您可以通過在內核堆上分配緩衝區（例如kmalloc()）或使用靜態/全局數據來實現此目的。