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

From: Srinivas Kandagatla
Date: Wed Dec 12 2018 - 07:26:33 EST

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;