[ewg] [PATCH 1/2 v2]libibvers: add create_qp_expanded

[Roland Dreier]

Sorry for jumping in so late in the process, but a few big concerns:

 >         struct ibv_qp *ibv_create_qp_expanded(struct ibv_pd *pd,
 >                                struct ibv_qp_init_attr *qp_init_attr,
 >                                uint32_t create_flags);

I don't like the name "_expanded" when all we are doing is adding a
flags parameter.  The next time we need to tweak this API, then we end
up with _extra_super_expanded or something like that.

I see two better options: keep the same prototype but call it something
like ibv_create_qp_with_flags (or maybe ibv_create_qp_flags), or keep
the name ibv_create_qp_expanded but instead of create_flags, have the
new parameter be ext_mask, have one bit in ext_mask indicate create
flags, and add create_flags to struct ibv_qp_init_attr -- then we can
add more extra stuff by using more bits in ext_mask.

Also, I wonder if it's worth a new verb in the kernel ABI for this.
Maybe we should add a new command in the ABI where libibverbs can pass
in a bitmask of supported extensions, and the kernel can respond with
which extensions it supports.  And then we can just continue to use the
reserved field in the existing create_qp command if both kernel and
userspace agree that they support create flags there.

 - R.