Linux Ethernet Bridging - Jan 2015 - [Bridge] [PATCH] bridge: only provide proxy ARP when CONFIG_INET is enabled

From: Cong Wang <cwang at twopensource.com>
Date: Tue, 13 Jan 2015 11:25:45 -0800
> On Tue, Jan 13, 2015 at 6:10 AM, Arnd Bergmann <arnd at arndb.de>
wrote:
>> When IPV4 support is disabled, we cannot call arp_send from
>> the bridge code, which would result in a kernel link error:
>>
>> net/built-in.o: In function `br_handle_frame_finish':
>> :(.text+0x59914): undefined reference to `arp_send'
>> :(.text+0x59a50): undefined reference to `arp_tbl'
>>
>> This makes the newly added proxy ARP support in the bridge
>> code depend on the CONFIG_INET symbol and lets the compiler
>> optimize the code out to avoid the link error.
>>
> 
> Not sure how much sense to make CONFIG_BRIDGE depend
> on CONFIG_INET, at least CONFIG_BONDING does.
It depends upon whether we want to provide and consider
as a valid configuration bridging without INET.  Probably
we do.

On 1/13/15 1:57 PM, David Miller wrote:
> From: Cong Wang <cwang at twopensource.com>
> Date: Tue, 13 Jan 2015 11:25:45 -0800
>
>> On Tue, Jan 13, 2015 at 6:10 AM, Arnd Bergmann <arnd at arndb.de>
wrote:
>>> When IPV4 support is disabled, we cannot call arp_send from
>>> the bridge code, which would result in a kernel link error:
>>>
>>> net/built-in.o: In function `br_handle_frame_finish':
>>> :(.text+0x59914): undefined reference to `arp_send'
>>> :(.text+0x59a50): undefined reference to `arp_tbl'
>>>
>>> This makes the newly added proxy ARP support in the bridge
>>> code depend on the CONFIG_INET symbol and lets the compiler
>>> optimize the code out to avoid the link error.
>>>
>>
>> Not sure how much sense to make CONFIG_BRIDGE depend
>> on CONFIG_INET, at least CONFIG_BONDING does.
>
> It depends upon whether we want to provide and consider
> as a valid configuration bridging without INET.  Probably
> we do.
Rather than connect CONFIG_BRIDGE to CONFIG_INET, why not make 
br_do_proxy_arp (and setting BR_PROXYARP flag) a no-op if CONFIG_INET is 
not set?

#ifdef CONFIG_INET
#else
static inline void br_do_proxy_arp(...args...)
{
}
#endif

That covers both arp_tbl and arp_send.

David

On Tuesday 13 January 2015 14:14:20 David Ahern wrote:
> 
> Rather than connect CONFIG_BRIDGE to CONFIG_INET, why not make 
> br_do_proxy_arp (and setting BR_PROXYARP flag) a no-op if CONFIG_INET is 
> not set?
> 
> #ifdef CONFIG_INET
> #else
> static inline void br_do_proxy_arp(...args...)
> {
> }
> #endif
> 
> That covers both arp_tbl and arp_send.
The effect is very similar to my patch (probably same object code), the
only difference should be that it would add an ugly #ifdef instead of
the preferred IS_ENABLED() check, so you don't get any compile-time
coverage of the function. It's not really important because everybody
has CONFIG_INET enabled in practice and it does get more than enough
compile-time coverage.

	Arnd