netdev - Re: [PATCHv6 bpf-next 2/3] sample/bpf: add xdp_redirect_map

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Date:   Fri, 10 Jul 2020 16:32:35 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Hangbin Liu <liuhangbin@...il.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Jiri Benc <jbenc@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>, ast@...nel.org,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Subject: Re: [PATCHv6 bpf-next 2/3] sample/bpf: add xdp_redirect_map_multicast
 test

On 7/10/20 8:41 AM, Hangbin Liu wrote:
> On Fri, Jul 10, 2020 at 12:40:11AM +0200, Daniel Borkmann wrote:
>>> +SEC("xdp_redirect_map_multi")
>>> +int xdp_redirect_map_multi_prog(struct xdp_md *ctx)
>>> +{
>>> +	long *value;
>>> +	u32 key = 0;
>>> +
>>> +	/* count packet in global counter */
>>> +	value = bpf_map_lookup_elem(&rxcnt, &key);
>>> +	if (value)
>>> +		*value += 1;
>>> +
>>> +	return bpf_redirect_map_multi(&forward_map, &null_map,
>>> +				      BPF_F_EXCLUDE_INGRESS);
>>
>> Why not extending to allow use-case like ...
>>
>>    return bpf_redirect_map_multi(&fwd_map, NULL, BPF_F_EXCLUDE_INGRESS);
>>
>> ... instead of requiring a dummy/'null' map?
> 
> I planed to let user set NULL, but the arg2_type is ARG_CONST_MAP_PTR, which
> not allow NULL pointer.

Right, but then why not adding a new type ARG_CONST_MAP_PTR_OR_NULL ?