Re: [PATCH] [media] uapi/media.h: Use u32 for the number of graph objects

[Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>]

On Thursday 17 December 2015 10:45:56 Mauro Carvalho Chehab wrote:
> If I understood well, he's proposing to do is:
> 
> struct media_v2_topology {
>         __u64 topology_version;
> 
>         __u32 num_entities;
>         __u32 num_interfaces;
>         __u32 num_pads;
>         __u32 num_links;
> 
>         __u64 ptr_entities;
>         __u64 ptr_interfaces;
>         __u64 ptr_pads;
>         __u64 ptr_links;
> };
> 
> The problem is that, if we latter need to extend it to add a new type
> the extension will not be too nice. For example, I did some experimental
> patches adding graph groups:
> 

Can you clarify how the 'topology_version' is used here? Is that
the version of the structure layout that decides how we interpret the
rest, or is it a number that is runtime dependent?

If this is an API version, I think the answer can simply be to drop
the topology_version field entirely, and use a new ioctl command code
whenever the API changes. This is the preferred method anyway.

	Arnd