Re: [PATCHv8 04/11] ib_core: IBoE CMA device binding

[Eli Cohen <eli-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>]

On Wed, May 12, 2010 at 01:14:33PM -0700, Roland Dreier wrote:
>  > Multicast GIDs are always mapped to multicast MACs
>  > as is done in IPv6. Some helper functions are added to ib_addr.h.  IPv4
>  > multicast is enabled by translating IPv4 multicast addresses to IPv6 multicast
>  > as described in
>  > http://www.mail-archive.com/ipng-Va8kgSFw1KyzQ7sTrsxvMkEOCMrvLtNR@public.gmane.org/msg02134.html.
> 
> I guess it's a bit unfortunate that the RoCE annex completely ignored
> how to map multicast GIDs to ethernet addresses (I suppose as part of
> the larger decision to ignore address resolution entirely).  Anyway,
> looking at the email message you reference, it seems to be someone
> asking what the right way to map IPv4 multicast addresses to IPv6
> addresses is.  Is there a more definitive document you can point to?

I am not aware of any definitive document that addresses this issue.

> 
> It seems that unfortunately the way the layering of addresses is done,
> there's no way to just use the standard mapping of IPv4 multicast
> addresses to Ethernet addresses (since IBoE is does addressing via
> the CMA mapping to GIDs followed by an unspecified mapping from GIDs to
> Ethernet addresses).
> 

It is natural to treat gids as IPv6 addresses, so using the standard
mapping from IPv6 multicast addresses to mac addresses seems reasonable.