设备映射程序'ioctl'签名

问题描述：

这个问题可能看起来很天真，但我是内核/驱动程序编程的新手。我在一个块设备上创建了一个设备映射器，该设备工作正常。它是构造函数/析构函数，并调用映射方法。设备映射程序'ioctl'签名

现在，我正在尝试为此映射器编写一个ioctl。当读写控制为装置写入，它具有以下特征：

int ioctl(int d, /* other args */);

的文件结构/描述符中的ioctl预期。由于它可以访问文件，因此应用程序进程可以轻松使用它。

但对于设备映射的IOCTL具有以下特征（在结构TARGET_TYPE）：

哪有用户应用程序可以访问与IOCTL设备映射器，而无需结构dm_target的知识呢？

答

-Ioctl which stand for Input Output control is a system call used in linux to implement system calls which are not be available in the 
kernel by default. 

-The major use of this is in case of handling some specific operations of a device for which the kernel does not have a system call by default. For eg: Ejecting the media from a "CD" drive. An ioctl command is implemented to give the eject system call to the cd drive. 

-ioctl(fd, cmd , INPARAM or OUTPARAM); 
      | 
     3rd arguement is INPARAM or OUTPARAM i.e we don't have to read a device, then how how to interact with device ? use ioctl. 

-open ioctl.h and check you will get more information 
    #define "ioctl name" __IOX("magic number","command number","argument type") 


static long char_dev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) 
{ 
    /* verify arguemenst using access_ok() */ 
    /* impliment support of ioctl commands */ 
}

设备映射程序'ioctl'签名

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