Re: [PATCH] vsock: ratelimit unknown ioctl error message

[Stefano Garzarella]

On Mon, Oct 26, 2020 at 09:46:17AM +0000, David Laight wrote:
> From: Stefano Garzarella
> > Sent: 26 October 2020 09:39
> >
> > On Mon, Oct 26, 2020 at 09:13:23AM +0000, David Laight wrote:
> > >From: Stefano Garzarella
> > >> Sent: 26 October 2020 08:43
> > >...
> > >> >Isn't the canonical error for unknown ioctl codes -ENOTTY?
> > >> >
> > >>
> > >> Oh, thanks for pointing that out!
> > >>
> > >> I had not paid attention to the error returned, but looking at it I
> > >> noticed that perhaps the most appropriate would be -ENOIOCTLCMD.
> > >> In the ioctl syscall we return -ENOTTY, if the callback returns
> > >> -ENOIOCTLCMD.
> > >>
> > >> What do you think?
> > >
> > >It is 729 v 443 in favour of ENOTTY (based on grep).
> >
> > Under net/ it is 6 vs 83 in favour of ENOIOCTLCMD.
> >
> > >
> > >No idea where ENOIOCTLCMD comes from, but ENOTTY probably
> > >goes back to the early 1970s.
> >
> > Me too.
> >
> > >
> > >The fact that the ioctl wrapper converts the value is a good
> > >hint that userspace expects ENOTTY.
> >
> > Agree on that, but since we are not interfacing directly with userspace,
> > I think it is better to return the more specific error (ENOIOCTLCMD).
>
> I bet Linux thought it could use a different error code then
> found that 'unknown ioctl' was spelt ENOTTY.

It could be :-)

Anyway, as you pointed out, I think we should change the -EINVAL with 
-ENOTTY or -ENOIOCTLCMD.

@Jakub what do you suggest?

Thanks,
Stefano