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

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Date: Tue, 22 Aug 2023 01:50:04 +0900
From: Vincent Mailhol <vincent.mailhol@...il.com>
To: Oliver Hartkopp <socketcan@...tkopp.net>
Cc: Jakub Kicinski <kuba@...nel.org>, Martin Hundebøll <martin@...nix.com>, 
	Wolfgang Grandegger <wg@...ndegger.com>, Marc Kleine-Budde <mkl@...gutronix.de>, 
	"David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>, Chandrasekar Ramakrishnan <rcsekar@...sung.com>, 
	linux-can <linux-can@...r.kernel.org>, netdev <netdev@...r.kernel.org>, 
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] can: netlink: support setting hardware filters

On Mon. 21 Aug. 2023 at 04:21, Oliver Hartkopp <socketcan@...tkopp.net> wrote:
> On 19.08.23 15:29, Vincent Mailhol wrote:
> > On Sat. 19 Aug. 2023 at 22:10, Vincent Mailhol
> > <vincent.mailhol@...il.com> wrote:
> >> On Sat. 19 Aug. 2023, 01:19, Jakub Kicinski <kuba@...nel.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.
>
> You are right with FDF where we could use the former CAN_ERR_FLAG value
> which is not needed for hw filter API.

And what about the BRS flag?

> But regarding CAN XL we could use the Standard 11 bit ID handling with
> another flag inside the remaining 18 bits.

Then, wouldn't you still need one more flag to indicate that this is a
CAN XL filter?

> The general concept of re-using the struct can_filter makes sense to me
> as this follows the widely used pattern in the af_can.c core and CAN_RAW
> sockets.
>
> Best regards,
> Oliver
>
> >
> >> 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