Re: How far back does rdma-core X supports the kernel Y?

[Jason Gunthorpe <jgg-uk2M96/98Pc@public.gmane.org>]

On Wed, Nov 01, 2017 at 08:22:37PM +0200, Yishai Hadas wrote:
> On 11/1/2017 8:00 PM, Jason Gunthorpe wrote:
> >>>          if (attr_mask & ~((1ULL << (IBV_QP_DEST_QPN + 1)) - 1))
> >>
> >>The above rdma-core code is correct, look at verbs.h:
> >>IBV_QP_DEST_QPN = 1 << 20,
> >
> >Okay, then it should be
> >
> >  if (attr_mask & ~(IB_QP_RATE_LIMIT - 1))
> >
> 
> Why the library should support values that were never exposed in verbs.h ?

I think Ram is explaining that the kernel rdma_cm provides the
attr_mask to use with modify_qp, and that the 4.3 kernel sets the
three now reserved bits. The expectation is that user space will flow
those bits and values from the kernel rdma_cm interface back to
uverbs.

Userspace never looks at the attr_mask, and it does not matter that
the values were never in verbs.h.

rdma-core is expected to work on 4.3, so if 4.3 is using this kind of
path, we cannot block it in userspace.

At least, I think that is what Ram is saying.

Jason
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