On 08/17/2017 12:28 PM, Jesper Dangaard Brouer wrote:
>
> On Thu, 17 Aug 2017 11:46:10 -0700 John Fastabend <john.fastab...@gmail.com>
> wrote:
>
>> On 08/17/2017 09:22 AM, Jesper Dangaard Brouer wrote:
>>> The return error code need to be included in the tracepoint
>>> xdp:xdp_redirect, else its not possible to distinguish successful or
>>> failed XDP_REDIRECT transmits.
>>>
>>> XDP have no queuing mechanism. Thus, it is fairly easily to overrun a
>>> NIC transmit queue. The eBPF program invoking helpers (bpf_redirect
>>> or bpf_redirect_map) to redirect a packet doesn't get any feedback
>>> whether the packet was actually transmitted.
>>>
>>> Info on failed transmits in the tracepoint xdp:xdp_redirect, is
>>> interesting as this opens for providing a feedback-loop to the
>>> receiving XDP program.
>>>
>>> Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com>
>>> ---
>>
>> [...]
>>
>>> @@ -2532,12 +2535,14 @@ int xdp_do_redirect(struct net_device *dev, struct
>>> xdp_buff *xdp,
>>> ri->map = NULL;
>>> if (unlikely(!fwd)) {
>>> bpf_warn_invalid_xdp_redirect(index);
I think we should drop the warn_invalid now that we have a tracepoint.
The tracepoint is much nicer for debugging vs a warning for what might
be a valid case depending on xdp program.
>>> - return -EINVAL;
>>> + err = -EINVAL;
>>> + goto out;
>>
>> It doesn't look like there is a check in trace_xdp_redirect to
>> avoid dereferencing a NULL fwd pointer here (*to in trace code
>> path). Did I miss something?
>
> Nice that you spotted this in your review, but the __string() macro
> used in trace code already takes case of this, see output:
>
> xdp:xdp_redirect: prog=39cf08f65683838a from=ixgbe2 to=(null)
> action=REDIRECT err=-22
Great thanks.
