Re: [PATCH 1/2] can: netlink: support setting hardware filters

[Vincent Mailhol <vincent.mailhol@gmail.com>]

On Sat. 19 Aug. 2023 at 22:10, Vincent Mailhol
<vincent.mailhol@gmail.com> wrote:
> On Sat. 19 Aug. 2023, 01:19, Jakub Kicinski <kuba@kernel.org> wrote:
> >
> > On Thu, 17 Aug 2023 12:10:13 +0200 Martin Hundebøll wrote:
> > > +             int len = nla_len(data[IFLA_CAN_HW_FILTER]);
> > > +             int num_filter = len / sizeof(struct can_filter);
> > > +             struct can_filter *filter = nla_data(data[IFLA_CAN_HW_FILTER]);
> >
> > This will prevent you from ever extending struct can_filter in
> > a backward-compatible fashion, right? I obviously know very little
> > about CAN but are you confident a more bespoke API to manipulate
> > filters individually and allow extensibility is not warranted?
>
> I follow Jakub's point of view.
>
> The current struct can_filter is not sound. Some devices such as the
> ES582.1 supports filtering of the CAN frame based on the flags (i.e.
> SFF/EFF, RTR, FDF).

I wrote too fast. The EFF and RTR flags are contained in the canid_t,
so the current struct can_filter is able to handle these two flags.
But it remains true that the CAN-FD flags (FDF and BRS) are currently
not handled. Not to mention that more flags will come with the
upcoming CAN XL.

> I think that each of the fields of the filter should have its own NLA
> declaration with the whole thing wrapped within a NLA_NESTED_ARRAY.
>
> I also think that there should then be a method to report the precise
> filtering capabilities of the hardware.
>
>
> Yours sincerely,
> Vincent Mailhol