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 12:07:07PM +0000, Amrani, Ram wrote:
> Hi All,
> I've installed rdma-core-15 on kernel 4.3 and ran into issues.
> 
> It seems this kernel doesn't include the following patch:
> https://github.com/torvalds/linux/commit/aa744cc01fe0f21dfbe2744d3fd5f2fb3244c9b3
> 
> So IB_QP_SMAC is present in kernel 4.3 but not in rdma-core-15.

> This caused a failure here:
>
> int ibv_cmd_modify_qp(struct ibv_qp *qp, struct ibv_qp_attr *attr,
>                       int attr_mask,
>                       struct ibv_modify_qp *cmd, size_t cmd_size)
> {
>         /*
>          * Masks over IBV_QP_DEST_QPN are only supported by
>          * ibv_cmd_modify_qp_ex.
>          */
>         if (attr_mask & ~((IBV_QP_DEST_QPN << 1) - 1))
>                 return EOPNOTSUPP;

WTF is this?

Based on the comment it should be:

         if (attr_mask & ~((1ULL << (IBV_QP_DEST_QPN + 1)) - 1))

To match the comment. And other places have the same mistake.

This was broken recently by 3ca7a1031486b588a7fbe0d262f8f89738215b58

Bodong??

> Do we expect these versions to operate?
> If not, from what version do we support backward compatibility?
> Are there any other backward compatibility issues you are aware of?

rdma-core should work with all kernel versions, anything else is a bad
bug.

Jason
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