netdev - Re: [PATCH v2 bpf-next 2/5] bpf: Add support to attach bpf program to a devmap entry

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Date:   Thu, 28 May 2020 15:54:16 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     David Ahern <dsahern@...nel.org>,
        Networking <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        john fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH v2 bpf-next 2/5] bpf: Add support to attach bpf program to
 a devmap entry

On Thu, May 28, 2020 at 3:40 PM David Ahern <dsahern@...il.com> wrote:
>
> On 5/28/20 1:01 AM, Andrii Nakryiko wrote:
> >
> > Please cc bpf@...r.kernel.org in the future for patches related to BPF
> > in general.
>
> added to my script
>
> >
> >>  include/linux/bpf.h            |  5 +++
> >>  include/uapi/linux/bpf.h       |  5 +++
> >>  kernel/bpf/devmap.c            | 79 +++++++++++++++++++++++++++++++++-
> >>  net/core/dev.c                 | 18 ++++++++
> >>  tools/include/uapi/linux/bpf.h |  5 +++
> >>  5 files changed, 110 insertions(+), 2 deletions(-)
> >>
> >
> > [...]
> >
> >>
> >> +static struct xdp_buff *dev_map_run_prog(struct net_device *dev,
> >> +                                        struct xdp_buff *xdp,
> >> +                                        struct bpf_prog *xdp_prog)
> >> +{
> >> +       u32 act;
> >> +
> >> +       act = bpf_prog_run_xdp(xdp_prog, xdp);
> >> +       switch (act) {
> >> +       case XDP_DROP:
> >> +               fallthrough;
> >
> > nit: I don't think fallthrough is necessary for cases like:
> >
> > case XDP_DROP:
> > case XDP_PASS:
> >     /* do something */
> >
> >> +       case XDP_PASS:
> >> +               break;
> >> +       default:
> >> +               bpf_warn_invalid_xdp_action(act);
> >> +               fallthrough;
> >> +       case XDP_ABORTED:
> >> +               trace_xdp_exception(dev, xdp_prog, act);
> >> +               act = XDP_DROP;
> >> +               break;
> >> +       }
> >> +
> >> +       if (act == XDP_DROP) {
> >> +               xdp_return_buff(xdp);
> >> +               xdp = NULL;
> >
> > hm.. if you move XDP_DROP case to after XDP_ABORTED and do fallthrough
> > from XDP_ABORTED, you won't even need to override act and it will just
> > handle all the cases, no?
> >
> > switch (act) {
> > case XDP_PASS:
> >     return xdp;
> > default:
> >     bpf_warn_invalid_xdp_action(act);
> >     fallthrough;
> > case XDP_ABORTED:
> >     trace_xdp_exception(dev, xdp_prog, act);
> >     fallthrough;
> > case XDP_DROP:
> >     xdp_return_buff(xdp);
> >     return NULL;
> > }
> >
> > Wouldn't this be simpler?
> >
>
> Switched it to this which captures your intent with a more traditional
> return location.
>
>         act = bpf_prog_run_xdp(xdp_prog, xdp);
>         switch (act) {
>         case XDP_PASS:
>                 return xdp;
>         case XDP_DROP:
>                 break;
>         default:
>                 bpf_warn_invalid_xdp_action(act);
>                 fallthrough;
>         case XDP_ABORTED:
>                 trace_xdp_exception(dev, xdp_prog, act);
>                 break;
>         }
>
>         xdp_return_buff(xdp);
>         return NULL;

looks good as well, thanks