Re: [PATCH 5/9] ib_uverbs: Add padding to end align ib_uverbs_reg_mr_resp

[Knut Omang <knut.omang-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>]

On Thu, 2016-09-01 at 20:09 -0600, Jason Gunthorpe wrote:
> On Fri, Sep 02, 2016 at 02:09:25AM +0200, Knut Omang wrote:
> > 
> > The ib_uverbs_reg_mr_resp structure was not 64 bit end aligned
> > as required by the protocol. This causes alignment issues
> > if a device specific driver needs to transfer extra response
> > arguments.
> Can you explain in the commit message why this doesn't break anything?
> How does compat work with existing libibverbs?

It doesn't, and I realize I need to handle both

old userspace -> new kernel
new userspace -> old kernel

I am working on a fix for it, which would have to be in ib_uverbs due to the 

if  ( <user size> != <kernel size> ) 
   fail

semantics which effectively inhibits any changes at all  :-/

Thanks,
Knut

> Jason
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