Abstracting struct ifnet

[Adrian Chadd]

Hi,

I honestly quite like this idea.



Adrian

On 16 February 2012 20:16, Marcel Moolenaar <marcel at xcllnt.net> wrote:
> All,
>
> Juniper is in the final phases of creating a clean separation
> between FreeBSD and Junos, so as to make upgrades of FreeBSD
> easier. This also allows Juniper to track -current and be more
> active FreeBSD contributors.
>
> To that end, we have a short-term and hopefully short-lived
> problem to solve, which is the ability to use FreeBSD's network
> drivers against the Junos network stack. As some may know, the
> Junos network stack has split up struct ifnet into a physical
> and logical component, called ifdev and iflogical.
>
> We've tried a few approaches to bridge the gap between ifnet
> on the one hand and ifdev and iflogical on the other and found
> that abstracting ifnet and using accessor functions is the
> best way to allow us to use FreeBSD drivers with the Junos
> network stack, while retaining the ability to use them with
> the FreeBSD stack.
>
> FreeBSD is also looking at breaking up ifnet and with that in
> mind, I was wondering if there would be any resistance to
> changing network drivers to use accessor functions or macros
> instead of direct pointer dereferences?
>
> For example, do something like:
>
> Index: if_fxp.c
> ===================================================================
> --- if_fxp.c    (revision 231178)
> +++ if_fxp.c    (working copy)
> @@ -823,13 +823,14 @@
>        }
>
>        if_initname(ifp, device_get_name(dev), device_get_unit(dev));
> -       ifp->if_init = fxp_init;
> -       ifp->if_softc = sc;
> -       ifp->if_flags = IFF_BROADCAST | IFF_SIMPLEX | IFF_MULTICAST;
> -       ifp->if_ioctl = fxp_ioctl;
> -       ifp->if_start = fxp_start;
> +       if_set_init(ifp, fxp_init);
> +       if_set_softc(ifp, sc);
> +       if_set_flags(ifp, IFF_BROADCAST | IFF_SIMPLEX | IFF_MULTICAST, 0);
> +       if_set_ioctl(ifp, fxp_ioctl);
> +       if_set_start(ifp, fxp_start);
>
> -       ifp->if_capabilities = ifp->if_capenable = 0;
> +       if_set_capabilities(ifp, 0);
> +       if_set_capenable(ifp, 0);
>
>        /* Enable checksum offload/TSO for 82550 or better chips */
>        if (sc->flags & FXP_FLAG_EXT_RFA) {
>
> Such a scheme, while initially touching a lot of driver,
> would make it easier to break up ifnet *and* also make it
> easier to hide ABI/API changes from driver vendors (esp.
> when the accessor functions are non-inlined functions and
> not macros or inlines). This is particularly useful for
> Juniper, where we have worked towards network stacks as
> (pre-)loadable modules so as to help with migration and
> validation.
>
> Thoughts, feedback and suggestion are welcome,
>
> --
> Marcel Moolenaar
> marcel at xcllnt.net
>
>
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