Issue in ioctl func call of character driver.

[KARTHIK SEKURU]

Hi,
I am new to kernel device drivers.

I wrote a simple character driver built statically having the fops as shown:

*static const struct file_operations mfcfpga65_usb_fops = {*
* .owner = THIS_MODULE,*
* .open = mfcfpga65_usb_open,*
* .read = mfcfpga65_usb_read,*
* .unlocked_ioctl = mfcfpga65_usb_ioctl,*
* .release = mfcfpga65_usb_close,*
*};*

All the driver registrations are done properly.

I wrote a sample application to test these drivers implementing open,read
and ioctl calls.

open and read are working fine whereas ioctl is not behaving as expected.

The application code is as shown:

*int main()*
*{*
* printf("Enterred main function : \n");*
* int fd=0,ret=0;*
* char buff[80]="";*
* *
* fd=open("/dev/usbmod",O_RDONLY);*
* if(fd<0) *
* {*
* printf("fd value is less than 0\n");*
* }*
* *
* printf("fd :%d\n",fd);*
* *
* ret=read(fd,buff,10);*
* buff[ret]='\0';*
*
*
*        printf("The commands passed are %d and
 %d\n",IOCTL_USB_READ,IOCTL_USB_OPEN );*
* ret = ioctl(fd,IOCTL_USB_READ);*
* ret = ioctl(fd,IOCTL_USB_OPEN); *
*
*
* close(fd);*
*}*

The cmds in ioctl are defined in seperate header file which is included in
driver as well as in the applicatin.That definations are as shown

*#define MFCFPGA65_NUM 254*
*
*
*#define IOCTL_USB_OPEN           _IO(MFCFPGA65_NUM,0)*
*#define IOCTL_USB_READ           _IO(MFCFPGA65_NUM,1)*
*#define IOCTL_USB_WRITE          _IO(MFCFPGA65_NUM,2)*


The IOCTL call in driver does nothing except printk in each switch case
showing to which case statement it entered .This ioctls implementation in
driver  is as shown below:

*static long mfcfpga65_usb_ioctl(struct inode *inode, struct file *file,
unsigned int iocmd,*
* unsigned long ioarg)*
*{*
*   *
* void __user *arg = (void __user *)ioarg;*
* unsigned int* stream;*
* unsigned int size;*
* *
* printk(KERN_INFO "In IOCTL function of USB character driver with cmd as
%d : \n",iocmd);*
* *
* printk(KERN_INFO "The switch case cmds are %d %d
%d\n",IOCTL_USB_OPEN,IOCTL_USB_READ,IOCTL_USB_WRITE);*
*
*
* switch (iocmd) {*
*
*
* case IOCTL_USB_OPEN:*
* *
* printk(KERN_INFO "In IOCTL case1 of USB character driver: \n");*
* return 0;*
* break;*
* *
* case IOCTL_USB_READ:*
* *
* printk(KERN_INFO "In IOCTL case2 of USB character driver: \n");*
* return 0;*
*         break;*
* *
* case IOCTL_USB_WRITE:*
* *
* printk(KERN_INFO "In IOCTL case3 of USB character driver: \n");*
* return 0;*
*            break;*
* *
*    }*
*}*

>From application i made sure that i am passing proper cmd arguments.The
control goes to the ioctl function call in driver but doesn't go to the
proper switch cases.

This is because the iocmd argument received in the ioctl implementation is
getting corrupted i.e eventhough from application i am passing *IOCTL_USB_READ
, **IOCTL_USB_OPEN *parameters,when i check them in
ioctl function in drivers the values are changed and through printk in the
ioctl i could see that the iocmd received in the function is 4096 value
which doesn't match to IOCTL_USB_READ or
IOCTL_USB_OPEN.

Please let me know how can the command argument passes via ioctl call in
application is modified/corrupted before it reaches the actual ioctl
implementation in drivers.

thanks,
Karthik.
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