netdev - Re: [PATCH V4 net-next 5/5] icmp: add response to RFC 8335 PROBE messages

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Message-ID: <46640b57-350b-e616-ad96-03fda82eb86d@gmail.com>
Date:   Sat, 20 Mar 2021 10:43:01 -0600
From:   David Ahern <dsahern@...il.com>
To:     Andreas Roeseler <andreas.a.roeseler@...il.com>,
        David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org, kuba@...nel.org,
        dsahern@...nel.org
Subject: Re: [PATCH V4 net-next 5/5] icmp: add response to RFC 8335 PROBE
 messages

On 3/20/21 10:01 AM, Andreas Roeseler wrote:
> On Wed, 2021-03-17 at 21:24 -0600, David Ahern wrote:
>> On 3/17/21 9:19 PM, David Miller wrote:
>>> From: Andreas Roeseler <andreas.a.roeseler@...il.com>
>>> Date: Wed, 17 Mar 2021 22:11:47 -0500
>>>
>>>> On Mon, 2021-03-15 at 04:35 +0800, kernel test robot wrote:
>>>> Is there something that I'm not understanding about compiling
>>>> kernel
>>>> components modularly? How do I avoid this error?
>>>
>>>>
>>> You cannot reference module exported symbols from statically linked
>>> code.
>>> y
>>>
>>
>> Look at ipv6_stub to see how it exports IPv6 functions for v4 code.
>> There are a few examples under net/ipv4.
> 
> Thanks for the advice. I've been able to make some progress but I still
> have some questions that I have been unable to find online.
> 
> What steps are required to include a function into the ipv6_stub
> struct? I've added the declaration of the function to the struct, but
> when I attempt to call it using <ipv6_stub->ipv6_dev_find()> the kernel
> locks up. Additionally, a typo in the declaration isn't flagged during
> compilation. Are there other places where I need to edit the ipv6_stub
> struct or include various headers? The examples I have looked at are
> <fib_semantics.c>, <nexthop.c>, and <udp.c> in the <net/ipv4> folder
> and they don't seem to do anything on the caller side of ipv6_stub, so
> I think I am not adding the function to ipv6_stub properly. I have been
> able to call other functions that currently exist in ipv6_stub, but not
> the one I  am attempting to add, so am I missing a step?

you probably did not add the default in net/ipv6/addrconf_core.c.

> 
> I've noticed that some functions such as <ipv6_route_input> aren't
> exported using EXPORT_SYMBOL when it is defined in
> <net/ipv6/af_inet6.c>, but it is still loaded into ipv6_stub. How can
> this be? Is there a different way to include symbols into ipv6_stub
> based on whether or not they are explicitly exported using
> EXPORT_SYMBOL?
> 

take a look at 1aefd3de7bc6 as an example of how to add a new stub.