Re: [PATCH,RFC] nfsd: Make INET6 transport creation failure an informational message

[Tom Tucker <tom-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org>]

Chuck Lever wrote:
> Hi Roland-
>
> On 04/02/2010 01:22 PM, Roland Dreier wrote:
>>   >  >  The write_ports code will fail both the INET4 and INET6 
>> transport
>>   >  >  creation if
>>   >  >  the transport returns an error when PF_INET6 is specified. 
>> Some transports
>>   >  >  that do not support INET6 return an error other than 
>> EAFNOSUPPORT.
>>   >
>>   >  That's the real bug.  Any reason the RDMA RPC transport can't 
>> return
>>   >  EAFNOSUPPORT in this case?
>>
>> I think Tom's changelog is misleading.  The problem is that the RDMA
>> transport actually does support IPv6, but it doesn't support the
>> IPV6ONLY option yet.  So if NFS/RDMA binds to a port for IPv4, then the
>> IPv6 bind fails because of the port collision.
>
> IPV6ONLY is a requirement for RPC over IPv6.  If the underlying 
> transport does not support IPV6ONLY, then it cannot properly support 
> RPC over IPv6.  It's easy enough to catch listener creation calls for 
> IPv6 on such transports, and simply return EAFNOSUPPORT until support 
> for IPV6ONLY can be provided.
>
> The __write_ports() interface is specifically designed to silently 
> fall back to IPv4-only when IPv6 transport creation fails with 
> ENOAFSUPPORT.  I don't see a good reason to change the generic logic 
> in __write_ports() if there is a problem with implementing RPC over 
> IPv6 in a specific transport capability.  __write_ports() will do the 
> right thing if the transport returns the correct error code.
>
>> Implementing the IPV6ONLY option for RDMA binding is probably not
>> feasible for 2.6.34, so the best band-aid for now seems to be Tom's
>> patch.
>
> My recent experience with similar changes suggests the specific 
> solution Tom proposed will trigger extra bug reports and e-mails, as 
> the change appears to affect non-RDMA transports as well.  This printk 
> might fire, for example, for INET transports on systems that are built 
> without IPv6 support, or where ipv6.ko is blacklisted in user space.
>
> In other words, I agree that there's a bug that should be addressed in 
> 2.6.34, and I don't have any problem with setting up only an IPv4 
> listener in this case.  But I think the addition of a printk that 
> fires for all transports in this case is problematic.
>
This makes sense to me.

> It would be better to address this in the RPC/RDMA transport 
> capability, and not in generic upper level logic.  We already have 
> correct behavior in __write_ports, and the RPC/RDMA transport 
> capability should be changed to use it.
>
So is seems reasonable to me to fail svc_create_xprt with ("rdma", 
PF_INET6) with EAFNOSUPPORT because the RDMA transport does not support 
the v4only setsockopt.

I will post a patch that does this.

Thanks,
Tom

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