How to pass data from driver to Application??

QNX DEVELOPERS Realtime and Embedded
1

Hi All,
I have an issue for devctl function. My client application needs the some data from a driver. So i started to do some R&d on it. I have implemented my own custom devctl function and replaced in the resource manager.

    But i am unable to get correct values passed from driver to application. Please help me out to understand more on devctl functionality.

Please have a look on my driver code.

int
custom_devctl(resmgr_context_t *ctp, io_devctl_t *msg, RESMGR_OCB_T *ocb)
{
int nbytes=0, status=0;
typedef union devctl_msg
{
int tx; //Filled by client on send
int rx; //Filled by server on reply
char errorString[512];
} data_t;

 	 union
 	 { 
 	 	 data_t data; 
 	 	 int data32; 
 	 }*rx_data; 

  if ((status = iofunc_devctl_default(ctp, msg, ocb)) != _RESMGR_DEFAULT)
 {  
    return(status);  
 }  

 /* 
 Note this assumes that you can fit the entire data portion of 
 the devctl into one message.   */
    
 rx_data = _DEVCTL_DATA(msg->i); 
	
 switch (msg->i.dcmd) 
 {  
       case DEVCTL_DSCGETERRORSTRING:
    	  
    	  printf("\n DEVCTL_DSCGETERRORSTRING command came");
    	  rx_data->data.rx = 10;   // Testing data
    	  
    	  strcpy(rx_data->data.errorString,"Some Error came");
    	  nbytes = sizeof(rx_data->data.errorString);
    	  
    	  // return data to the client
    	  memset(&msg->o,0,sizeof(msg->o));
    	  msg->o.nbytes = nbytes;
    	  
    	  SETIOV (ctp -> iov, &msg -> o, sizeof (msg -> o) + nbytes);
    	  return (_RESMGR_NPARTS (2));
    	 break;
    
      default:  
         printf ("command unknown \n" );      

  }

return( _RESMGR_PTR(ctp, &msg->o, sizeof(msg->o) + nbytes));

}

On application side, i am getting correct string under rx_data->data.errorString but  rx_data->data.rx is coming as wrong value(15645345). 
            It would be better, if i get good link on devctl for passing data.
2

Garyritu,

This union

typedef union devctl_msg
{
int tx; //Filled by client on send
int rx; //Filled by server on reply
char errorString[512];
} data_t;

means that you can either have

rx_data->data.rx = 10; // Testing data

OR

strcpy(rx_data->data.errorString,“Some Error came”);

but not both. The strcpy is over writing the rx variable because there is only 512 bytes in the union, not 512 + 2 int’s. You want a struct not a union.

Tim

3

Or if applicable you can implement support for read() instead of using ioctl(). If read() is already used for other type of data, you could setup a different mount point, something like /dev/xxx_log or /dev/xxx/log.

I always favor that option because ioctl are hard to do from a shell ;-)