Dmitry Torokhov wrote:

On Fri, Feb 15, 2013 at 03:51:41PM +0200, Kirill A. Shutemov wrote:

quoted

Johan Hedberg wrote:

quoted

Hi David,

On Fri, Feb 15, 2013, David Herrmann wrote:

quoted

On Fri, Feb 15, 2013 at 12:29 PM, Kirill A. Shutemov
[off-list ref] wrote:

quoted

Hi David and all,

There's claim in uhid.h that the interface is "compatible even between
architectures". But it obviously is not true: struct uhid_create_req
contains pointer which breaks everything.

The easy way to demonstrate the issue is compile uhid-example.c with -m32
and try to run it on 64 bit kernel. Creating of the device will fail.

Indeed, we missed that. We should probably also notify the HIDP
developers as "struct hidp_connadd_req" suffers from the same
problems. (CC'ed)

quoted

I don't see an easy way to fix this. Few options:

1. Replace the pointer with u64. It will fix the issue, but it breaks ABI
   which is never a good idea. Not sure how many users interface already
   has.

The only users I am aware of is an HID debugging tool and experimental
HoG Bluetooth support (bluez). Maybe Marcel or Johan can comment
whether this is already used by bluez-5? If it is, then we shouldn't
break ABI and go with #2+#3. Otherwise, I think changing to u64 should
be ok.
On the other hand, it would break any future build for older stable
kernels so not breaking ABI is probably the best idea. Any comments? I
can add a COMPAT fix and a comment to fix this in the next version of
UHID_CREATE.

The HoG code in BlueZ 5 does indeed use this API and it's also not
anymore behind any kind of experimental flag (i.e. it is an officially
supported feature).

Johan

Here's my attempt to fix the issue.

Not sure if tricks with padding in a good idea. We can  just use __u64
instead of pointer, but it will require update of userspace to silence
cast warning and will cause warning if you will try to use updated
userspace with old kernel headers.

Any comments?

This does not fix anything really, we simply have to deal with compat
interface.

Compiled but not tested.

Works for me.

Acked-by: Kirill A. Shutemov <redacted>

Comment in uhid.h about cross-arch compatibility should be
removed since it's false.

-- 
 Kirill A. Shutemov