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 [off-list ref] wrote:

On 5/28/20 1:01 AM, Andrii Nakryiko wrote:

quoted

Please cc bpf@vger.kernel.org in the future for patches related to BPF
in general.

added to my script

quoted

quoted

 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(-)

[...]

quoted

+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 */

quoted

+       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