ioctl number change / backwards compatibility doubt

[Paulo Miguel Almeida]

On Sun, Jan 23, 2022 at 12:04:48PM +0100, Greg KH wrote:
> On Sun, Jan 23, 2022 at 08:55:30PM +1300, Paulo Miguel Almeida wrote:
> > 
> > I googled a fair bit of time and I'm 99% confident that there isn't such
> > userspace/lib tool so I guess this will have done the hard way :(
> 
> If there is no tool, why was the ioctl code written at all?  Something
> had to call it.
> 

when you told me to look for the userspace tool that interfaced with the
ioctl, my interpretation was that you were referring to something akin
to what /usr/bin/uname utility is to the syscall uname. Please correct me 
if I'm wrong.

re: what calls the ioctl created by the driver.

I'm led to believe that users of this driver make ioctl sycall
invocations directly from their application's source code like this:

#include "pi433_if.h"		/* userspace driver header */
#include <sys/ioctl.h>		/* ioctl */

int file_desc = open("/dev/pi433.0", O_RDWR);
struct pi433_tx_cfg tx_cfg = {
	.frequency = 433000000,
	.bit_rate = 4800,
	<omitted for brevity>...
};

int ret_val = ioctl(file_desc, PI433_IOC_WR_TX_CFG, tx_cfg);
....

thanks,

Paulo Almeida