linux-kernel - Re: [PATCH RFC 3/4] iio: add support for multiple scan types per channel

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Date: Sun, 26 May 2024 08:53:19 -0500
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>, 
	Michael Hennerich <Michael.Hennerich@...log.com>, Nuno Sá <nuno.sa@...log.com>, 
	Julien Stephan <jstephan@...libre.com>, Esteban Blanc <eblanc@...libre.com>, linux-iio@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 3/4] iio: add support for multiple scan types per channel

On Sun, May 26, 2024 at 7:11 AM Jonathan Cameron <jic23@...nel.org> wrote:
>
> On Sat, 25 May 2024 12:04:46 -0500
> David Lechner <dlechner@...libre.com> wrote:
>
> > On 5/25/24 11:14 AM, Jonathan Cameron wrote:
> > > On Fri, 24 May 2024 10:56:55 -0500
> > > David Lechner <dlechner@...libre.com> wrote:
> > >
> > >> On 5/20/24 11:12 AM, Jonathan Cameron wrote:
> > >>> On Mon, 20 May 2024 08:51:52 -0500
> > >>> David Lechner <dlechner@...libre.com> wrote:
> > >>>
> > >>>> On 5/19/24 2:12 PM, Jonathan Cameron wrote:
> > >>>>> On Tue,  7 May 2024 14:02:07 -0500
> > >>>>> David Lechner <dlechner@...libre.com> wrote:
> > >>>>>

..

> >
> > Maybe we are talking about two different things but calling them the same thing?
>
> I'm not sure.  Sounds like we both think our point is entirely obvious and clearly
> it isn't :(
>
> > > Key is the complete lack of
> > > association between what is returned by the get_current_scan_type() callback
> > > and this ext_scan_type array.
> >
> > Why would the caller of get_current_scan_type() need to know that the
> > returned value is associated with ext_scan_type?
>
> Because you are validating ext_scan_type, not the return of get_current_scan_type().
> They may or may not include the same data - to make this a good interface, that isn't
> error prone, get_current_scan_type() must return one that has been validated - i.e.
> is in the ext_scan_type array.
>
> I've looked several times and maybe I'm just failing to spot what ensures the validation
> is sufficient.
>

Ah, I finally get it now. I was having tunnel vision and it didn't
even occur to me that someone might be tempted to return anything that
wasn't a pointer to the ext_scan types array.

> >
> > >
> > > So either:
> > > 1) Make it do so - easiest being to return an index into the array rather than
> > >    a possibly unrelated scan_type -
> >

This option 1) makes sense to me now.

Do we also need to validate that the index returned is <
num_ext_scan_types in iio_get_current_scan_type()?