[ewg] Re: [ofa-general] OFED 1.3 Beta release is available

[Jack Morgenstein]

On Wednesday 05 December 2007 17:45, Tang, Changqing wrote:
> > I think the only alternative we have to preserve backwards
> > compatibility is to leave struct ibv_context_ops alone and
> > change the structure to:
> >
> > struct ibv_context {
> >         struct ibv_device      *device;
> >         struct ibv_context_ops  ops;
> >         int                     cmd_fd;
> >         int                     async_fd;
> >         int                     num_comp_vectors;
> >         pthread_mutex_t         mutex;
> >         void                   *abi_compat;
> >         struct ibv_xrc_op      *xrc_ops;
> > };
> >
> > with xrc_ops added at the end.  It's my fault for not making
> > the ops member a pointer I guess.
> >
> > Tziporet/Jack/whoever -- please fix up the libibverbs you
> > ship for OFED 1.3 to resolve this.
> >
> > We can clean this up for libibverbs 1.2 when the ABI can
> > change, if/when we have something worth breaking the ABI for.
> 

We need to have all userspace libraries set their private context object to 0 at allocation time
(the private context object includes the ibv_context structure, which must now be NULL-ed out).

The other userspace driver libraries (e.g., libmthca) do not zero-out their internal userspace
context structures (e.g., mthca_context) which include the ibv_context structure as the first element.
Up to now, we depended on the ibv_context assign to set unavailable verb implementations to NULL.
(and every userspace driver assigned the ops structure, with unimplemented operations set to NULL by the compiler).
This is no longer true.

Thus, anyone installing OFED will have a compatible set of userspace drivers for XRC applications
(drivers which do not implement XRC will return errors for XRC-verbs).

Applications which were compiled with previous libraries will still work (since they do not use XRC).

- Jack