[openib-general] Re: ANNOUNCE: First usable version of userspace verbs

[Libor Michalek]

On Thu, Feb 24, 2005 at 10:40:09AM -0800, Roland Dreier wrote:
>     Michael> The pingpong test fails for me, on x86_64. (The
>     Michael> executable being a 64 bit one). My kernel is 2.6.10.
> 
> OK, I installed x86_64 userspace and got user verbs working.  The
> first problem you ran into was because on a 32-bit arch,
> 
>     struct {
>             uint64_t a;
>             uint32_t b;
>     };
> 
> has size 12 but on a 64-bit arch it has size 16.  Because of the way I
> tested sizes of parameters passed into the kernel, it was basically
> looking for userspace to pass a size of 12.  I fixed this by padding
> all the structs to a multiple of 8 bytes so we don't run into this.

I'm curious, why pad the structure instead of using the packed attribute?

     struct {
             uint64_t a;
             uint32_t b;
     } __attribute__ ((packed));


Thanks.

-Libor