Issue with ioctl commands - Linux version 2.6.35.7+

[Alexandru Juncu]

On Tue, Dec 27, 2011 at 1:39 PM, Chetan Nanda <chetannanda at gmail.com> wrote:
> Hi All,
>
> I am facing a strange issue with the ioctl commands, and not able to find
> what wrong I am doing.
> I am trying with a dummy kernel driver and implemented ioctl command as
> follow:
>
> in my_ioctl.h
> #define READHWREG_MAGIC_NUMBER 0x15
> #define READHWREG_CAM_READPE _IOR(READHWREG_MAGIC_NUMBER, 1, int*)
>
> But the value of 'READHWREG_CAM_READPE' is comes out to be different in
> userspace (in the application) and kernel space (in the driver).
>
> In userspace I used ioctl as
> ...
>    printf("\ncommand %x \n",READHWREG_CAM_READPE); <-- command 80041501
>    error = ioctl(g_DevFileId, READHWREG_CAM_READPE);
> ..
>
> In kernel space
>
> int readHwReg_ioctl(struct inode *node, struct file *filp, unsigned int
> cmd,  unsigned long arg)
> {
> ...
>    printk("\n%d %s cmd = %x\n",__LINE__,__FUNCTION__,cmd); <--- cmd =
> bee6a9d4
> ...
> }
>
>
> I am not able to figure out the root cause,
> Please help to check...

I think that the command is actually sent via the arg parameter, which
is an address (it's a pointer to the value your are sending to kernel
space).