Re: [PATCH v3 3/4] can: skb:: move can_dropped_invalid_skb and can_skb_headroom_valid to skb.c

[Oliver Hartkopp]

On 5/17/22 14:39, Max Staudt wrote:
> On Tue, 17 May 2022 14:21:53 +0200
> Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx> wrote:
>
> > On 17.05.2022 14:14:04, Max Staudt wrote:
> > > > After looking through drivers/net/can/Kconfig I would probably
> > > > phrase it like this:
> > > >
> > > > Select CAN devices (hw/sw) -> we compile a can_dev module. E.g.
> > > > to handle the skb stuff for vcan's.
> > > >
> > > > Select hardware CAN devices -> we compile the netlink stuff into
> > > > can_dev and offer CAN_CALC_BITTIMING and CAN_LEDS to be compiled
> > > > into can_dev too.
> > > >
> > > > In the latter case: The selection of flexcan, ti_hecc and
> > > > mcp251xfd automatically selects CAN_RX_OFFLOAD which is then also
> > > > compiled into can_dev.
> > > >
> > > > Would that fit in terms of complexity?
> > >
> > > IMHO these should always be compiled into can-dev. Out of tree
> > > drivers are fairly common here, and having to determine which kind
> > > of can-dev (stripped or not) the user has on their system is a
> > > nightmare waiting to happen.
> >
> > I personally don't care about out-of-tree drivers.
>
> I know that this is the official stance in the kernel.
>
> But out-of-tree drivers do happen on a regular basis, even when
> developing with the aim of upstreaming. And if a developer builds a
> minimal kernel to host a CAN driver, without building in-tree hardware
> CAN drivers, then can-dev will be there but behave differently from
> can-dev in a full distro. Leading to heisenbugs and wasting time. The
> source of heisenbugs really are the suggested *hidden* Kconfigs.
>
>
> On another note, is the module accounting overhead in the kernel for
> two new modules with relatively little code in each, code that almost
> always is loaded when CAN is used, really worth it?

Oh, I didn't want to introduce two new kernel modules but to have 
can_dev in different 'feature levels'.

I would assume a distro kernel to have everything enabled with a full 
featured can_dev - which is likely the base for out-of-tree drivers too.

But e.g. the people that are running Linux instances in a cloud only 
using vcan and vxcan would not need to carry the entire infrastructure 
of CAN hardware support and rx-offload.

Best regards,
Oliver