Re: ioctl() and driver function d_ioctl return values

[Martin Husemann <martin%duskware.de@localhost>]

On Mon, May 19, 2025 at 05:12:37PM +0200, Beesdeckar wrote:
> Hello,
> 
> I am calling ioctl() with control code created with __IOWR() macro and third
> argument contains address of user-mode structure.
> When module's d_ioctl() returns non-zero value then user-mode ioctl()
> returns always -1 and structure in user mode does not contain data filled by
> module.
> 
> Are both above things by design ?

Yes, see src/sys/kern/sys_generic.c line 677ff:

                /*
                 * Copy any data to user, size was
                 * already set and checked above.
                 */
                if (error == 0 && (com&IOC_OUT) && size) {
                        error = copyout(data, SCARG(uap, data),
                            zero_size(size));
                        ktrgenio(SCARG(uap, fd), UIO_READ, SCARG(uap, data),
                            size, error);
                }

Only if the ioctl() succeeds (errror == 0) the copyout of the output structure
is done.

Martin