[openib-general] Re: [PATCH] RFC Verbs: add support for transport specific verbs

[Michael S. Tsirkin]

Quoting r. Fabian Tillier <ftillier at silverstorm.com>:
> Subject: Re: [PATCH] RFC Verbs: add support for transport specific verbs
> 
> On 2/28/06, Sean Hefty <mshefty at ichips.intel.com> wrote:
> > Sean Hefty wrote:
> > > Add support for transport specific extensions to the ib_device verbs.
> > > Relocate process_mad as an IB specific verb.
> > >
> > > This provides a mechanism to add iWarp specific functionality, such as
> > > the iWarp CM calls, to ib_device.
> >
> > Third proposal from Fab:
> >
> > struct rdma_device {
> >        most everything
> > };
> >
> > struct ib_device {
> >        struct rdma_device dev;
> >        IB specific operations;
> > };
> >
> > Of course, this is a much larger change.

And this still means we add complexity (need to verify device type)
for calling transport-specific functions, which also has performance
implications.

> Perhaps, but it is probably the cleanest solution, allowing iWarp and
> IB specific stuff to be totally independent with no header
> interdependencies between the two transports.  It also follows the
> existing precendent of how struct device is the first member of struct
> ib_device.

In linux we dont care about binary compatibility for kernel modules.
So the fact that structure size changes because an extra callback is
added does not introduce a dependency.

> While it is a larger change, I don't think it's particularily more
> complicated or more difficult - it's just bigger.
> 
> - Fab

Its also less safe since we add downcasts.

-- 
Michael S. Tsirkin
Staff Engineer, Mellanox Technologies