Re: [RFC PATCH 3/3] libibverbs: Add reg/unreg I/O memory verbs

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

On Thu, Jul 29, 2010 at 01:07:36PM -0700, Ralph Campbell wrote:

> > @@ -640,6 +640,9 @@ struct ibv_context_ops {
> >  					    size_t length,
> >  					    int access);
> >  	int			(*dereg_mr)(struct ibv_mr *mr);
> > +        struct ibv_mr *         (*reg_io_mr)(struct ibv_pd *pd, void *addr, size_t length,
> > +					     int access);
> > +        int                     (*dereg_io_mr)(struct ibv_mr *mr);
> >  	struct ibv_mw *		(*alloc_mw)(struct ibv_pd *pd, enum ibv_mw_type type);
> >  	int			(*bind_mw)(struct ibv_qp *qp, struct ibv_mw *mw,
> >  					   struct ibv_mw_bind *mw_bind);
> 
> Doesn't adding these in the middle of the struct break the
> libibverbs to libxxxverbs.so binary interface?
> Shouldn't they be added at the end of the struct?
> I'm not sure how the versioning works between libibverbs and
> device plugins. Don't we need to protect against libibverbs
> being upgraded but the libxxxverbs.so being older?

Adding them at all, anywhere, breaks the ABI, and needs a soname bump
of libibverbs. Last time this was done a versioned symbol approach was
used to try and keep handling a 1.0 ibv_context structure, but that
only works some times and breaks in corner cases :(

Jason
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