Re: [PATCH 1/2] rdma/cm: support option to allow manually setting IB path

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Wed, Oct 21, 2009 at 06:07:54PM -0700, Sean Hefty wrote:
> >I'm reluctant to override fields like this to save 4 bytes. The
> >clarity and extensibility of using an additional flags field seems
> >worth it to me, and the processing code is not complex. I cannot think
> >of a motivation to save the 4 bytes?
> 
> I wasn't thinking about saving the 4 bytes.  struct ib_user_path_rec is already
> part of the ABI for query route.  If the preference were used to indicate
> primary versus alternate path, which seems reasonable, then query route can more
> easily convey that information.

I'm not sure why we need to conflate these two functions..

But ucma_abi_query_route_resp is already broken as soon as the kernel
can support more than 2 paths on a QP. The entire point of the flags
scheme is to support more than 2 paths in future.

So ucma_abi_query_route_resp has to be churned in the future, and at
that time it can be synch'd to use the same structure as the path
update, and ibv_kern_path_rec can go away.

In light of that, I'd say pick the flag + raw PR method. That clearly
has the best long term API.

Jason
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