[ofa-general] Re: IB/core: Add creation flags to QPs

[Jack Morgenstein]

On Wednesday 26 March 2008 13:02, Or Gerlitz wrote:
> How about making the qp_type field a bit mask, such that in the ipoib 
> LSO use case it would be (UD | LSO) and in the ipoib ehca case (UD | 
> LL), etc. The bit mask change would also be propagated up to libibverbs 
> and be defined in a way such that it preserves backward compatibility re 
> the qp_type field for users of libibverbs that did not changed their code.
> 
You can't have your cake and eat it too.  You can't both use a bitmap
and preserve backwards compatibility.

The current QP types are:
enum ib_qp_type {
	/*
	 * IB_QPT_SMI and IB_QPT_GSI have to be the first two entries
	 * here (and in that order) since the MAD layer uses them as
	 * indices into a 2-entry table.
	 */
	IB_QPT_SMI,
	IB_QPT_GSI,

	IB_QPT_RC,
	IB_QPT_UC,
	IB_QPT_UD,
	IB_QPT_XRC,
	IB_QPT_RAW_IPV6,
	IB_QPT_RAW_ETY
};

This means that we are using the 3 LSBs in an enumerated fashion (integers 0..7), so
we can't use a bitmap here.  This leads us to a mixed field anyway --
3 bits for existing QP types (integers 0..6), and 29 bits of bit-map.

Why not just keep things separate, and use the enumeration as is for the existing types,
and keep the bitmap as a separate "flags" field -- this is much cleaner.

- Jack