Hi,

Generally we use any one of the follwing macros to define any ioctl command.
_IO(): For a command that has no arguement
_IOR(): For copying data to user space
_IOW(): For copying data from user space
_IORW(): For copying data from user to kernel and kernel to user
But in my driver, I have used _IO() macro to define all my ioctl commands and I have used an arguemnet and I do copy arguement data from user to kernel and kernel to user. My driver is working fine. I want to know, what is fundamental difference among all above macros?

Thanks and best regards,
Ganga