Re: [PATCH v8 44/55] [media] uapi/media.h: Add MEDIA_IOC_G_TOPOLOGY ioctl

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

On Tuesday 08 December 2015 17:23:40 Mauro Carvalho Chehab wrote:
> > > +
> > > +struct media_v2_topology {
> > > +   __u32 topology_version;
> > > +
> > > +   __u32 num_entities;
> > > +   struct media_v2_entity *entities;
> > 
> > The kernel seems to be moving to using __u64 instead of pointers in userspace-
> > facing structures to avoid compat32 code.
> 
> We had such discussion at the MC summit. I don't object to change to
> __u64, but we need to reach a consensus 
> 

Just saw the email fly by. Using a __u64 to pass a pointer is generally
the preferred method for most subsystems these days.

However, that means you probably want to extract the pointer from
that using something like

static inline void __user *get_upointer(u64 arg)
{
	return (void __user *)(uintptr_t)arg;
}

This is the only way that I know that works on both 32-bit and 64-bit
architectures as well as the oddball s390 compat mode (which you don't
care about because there are no media devices on s390).

	Arnd