netdev - Re: [bpf-next v2 8/9] bpf: Provide helper to do forwarding lookups in kernel FIB table

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Date:   Mon, 7 May 2018 08:26:47 -0600
From:   David Ahern <dsahern@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     netdev@...r.kernel.org, borkmann@...earbox.net, ast@...nel.org,
        davem@...emloft.net, shm@...ulusnetworks.com,
        roopa@...ulusnetworks.com, toke@...e.dk, john.fastabend@...il.com
Subject: Re: [bpf-next v2 8/9] bpf: Provide helper to do forwarding lookups in
 kernel FIB table

On 5/7/18 8:10 AM, Daniel Borkmann wrote:
> On 05/07/2018 03:35 PM, Jesper Dangaard Brouer wrote:
>> On Thu,  3 May 2018 19:54:31 -0700 David Ahern <dsahern@...il.com> wrote:
>>
>>> diff --git a/net/core/filter.c b/net/core/filter.c
>>> index 6877426c23a6..cf0d27acf1d1 100644
>>> --- a/net/core/filter.c
>>> +++ b/net/core/filter.c
>> [...]
>>> +static const struct bpf_func_proto bpf_xdp_fib_lookup_proto = {
>>> +	.func		= bpf_xdp_fib_lookup,
>>> +	.gpl_only	= true,
>>
>> Is it a deliberate choice to require BPF-progs using this helper to be
>> GPL licensed?
>>
>> Asking as this seems to be the first network related helper with this
>> requirement, while this is typical for tracing related helpers.
> 
> Good point, we should remove that. In networking it's only the perf event
> output helpers tying into tracing bits. After all, if you do a route lookup
> via netlink from user space there's no such restriction at all.
> 

Networking symbols are typically exported GPL for modules. The person
writing the code and exporting GPL is specifying a desire that only GPL
licensed modules can link to the symbol.

Given the common analogy of modules and bpf programs, why can't a writer
of a bpf helper specify a preference that only GPL licensed programs
leverage a BPF helper?