Re: [PATCH v2 6/6] misc: fastrpc: Add support for compat ioctls

[Srinivas Kandagatla]

> > > What prevents you from doing that and requiring compat support?
> > I removed most of the compat IOCTLS except this one.
> > The reason is that this ioctl takes arguments which can vary in number for
> > each call.
>
> Then do not do that :)
>
> Remember, you get to design the api, fix the structure size to work
> properly everywhere.
>
> > So args are passed as pointer to structure, rather than fixed
> > size. I could not find better way to rearrange this to give a fixed size
> > data structure. In theory number of arguments can vary from 0-255 for both
> > in & out.
> >
> > current data structure looks like this:
> >
> > struct fastrpc_invoke_args {
> > 	__s32 fd;
> > 	size_t length;
> > 	void *ptr;
> > };
>
> Make length and ptr both __u64 and you should be fine, right?  If you do
> that, might as well make fd __u64 as well to align things better.

That is fine for the args structure, but below "args" pointer in "struct 
fastrpc_invoke" is still not fixed size, unless we change that to __u64 
pointing to array of struct fastrpc_invoke_args. I have seen such usages 
in i915_drm.h.
Is that the preferred?

> > struct fastrpc_invoke {
> > 	__u32 handle;
> > 	__u32 sc;
> > 	struct fastrpc_invoke_args *args;
> > };
> > --srini