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

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Message-ID: <20200710064145.GA2531@dhcp-12-153.nay.redhat.com>
Date:   Fri, 10 Jul 2020 14:41:45 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
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 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.

Thanks
Hangbin